# Main group elements

## Main-group element

Set of elements consisting of Groups 1, 2 and 13 to 18 in the periodic table

The periodic tableof the chemical elements. The columns represent the groups. Groups 1, 2 and 13 to 18 constitute the main group. Sometimes groups 3 and 12, as well as the lanthanides and actinides (the two rows at the bottom), are also included in the main group.

In chemistry and atomic physics, the main group is the group of elements (sometimes called the representative elements) whose lightest members are represented by helium, lithium, beryllium, boron, carbon, nitrogen, oxygen, and fluorine as arranged in the periodic table of the elements. The main group includes the elements (except hydrogen, which is sometimes not included) in groups 1 and 2 (s-block), and groups 13 to 18 (p-block). The s-block elements are primarily characterised by one main oxidation state, and the p-block elements, when they have multiple oxidation states, often have common oxidation states separated by two units.

Main-group elements (with some of the lighter transition metals) are the most abundant elements on earth, in the solar system, and in the universe.

Group 12 elements are often considered to be transition metals; however, zinc (Zn), cadmium (Cd), and mercury (Hg) share some properties of both groups, and many scientists believe they should be included in the main group.[1][2] Occasionally, even the group 3 elements as well as the lanthanides and actinides have been included, because especially the group 3 elements and lanthanides are electropositive elements with only one main oxidation state like the group 1 and 2 elements. The position of the actinides is more questionable, but the most common and stable of them, thorium (Th) and uranium (U), are similar to main-group elements as thorium is an electropositive element with only one main oxidation state (+4), and uranium has two main ones separated by two oxidation units (+4 and +6).[3]

In older nomenclature, the main-group elements are groups IA and IIA, and groups IIIB to 0 (CAS groups IIIA to VIIIA). Group 12 is labelled as group IIB in both systems. Group 3 is labelled as group IIIA in the older nomenclature (CAS group IIIB).

### Bibliography

• Ralf Steudel, "Chemie der Nichtmetalle" (Chemistry of the nonmetals), 2nd Edition. Walter deGruyter, Berlin 1998. ISBN 3-11-012322-3
Sours: https://en.wikipedia.org/wiki/Main-group_element

## Elements

Elements are arranged by reactivity in the periodic table.  Elements with similar reactivity are put into the same column or group.  Some of these groups have special names.  The elements in group IA are called the alkali metals. The elements in group IIA are called the alkaline earth metals.  The elements in group VIIA are called the halogens and the elements in group VIIIA are called the noble gases or the inert gases.  The metals in group IB (copper, silver and gold) are sometimes called the coinage metals.  The columns with B (IB through VIIIB) are called the transition elements.  The columns with A (IA through VIIIA) are called the main group elements

The elements can also be divided into two main groups, the metals and the non-metals.  Metals are typically have a metallic sheen (shiny) are malleable (bendable) and conduct electricity.  Nonmetals typically do not show these properties.  There are some elements that show some, but not all, of the metallic properties.  These elements are called metalloids and are labeled here are semi-conductors.

Electrons are the “glue” that hold atoms together in compounds.  It is the outer shell electrons that form these bonds between atoms.  The first two quantum numbers n  (the shell) and l (the subshell) are both important in understanding bonding.  In this class we focus on the shell.  The shells correspond to the orbits of the Bohr model.  (See lecture 10.3)

The first shell is the smallest so it can only hold a maximum of 2 electrons.  The second shell can only hold a maximum of 8 electrons.  The third shell can only hold a maximum of 18 electrons but is particularly stable at 8 electrons.

Because it is the outer shells that react, we are most interested in the outer shell electrons.  We can represent the number of electrons in the outer shell with dots.  The outer shell are given the name valence electrons.  Officially, the valence electrons are the electrons in the outer shell of the uncharged atom.  Chlorine has 7 electrons in its outer shell and so can represent it as a “Cl” with seven dots around it.

becomes .  Notice how 2 electrons in the first shell and the 8 electrons in the second are inner shell electrons and are not written with dots.  Here is a chart of the main group elements and their Lewis dot symbols.

Notice that for the main group elements, the number of valence electrons is equal to the group number.

Sours: https://web.fscj.edu/milczanowski/psc/lect/ch9/slide3.htm

The main group elements are the chemical elements belonging to the s-block and p-block on the periodic table. These are elements in group 1 and group 2 (s-block) and groups 13 through 18 (p-block). In older IUPAC group numbering systems, the main group elements are groups IA, IIA, and IIIA to VIIIA. When the periodic table is divided in this manner, the other main element categories are the transition metals and the inner transition metals.

The s-block elements are the alkali metals and alkaline earth metals. The p-block elements are the basic metals, metalloids, nonmetals, halogens, and noble gases. Examples of main group elements include helium, lithium, boron, carbon, nitrogen, oxygen, fluorine, and neon.

Elements that are not main group elements are the transition metals (such as titanium, copper, and gold), the lanthanides (such as lanthanum and erbium), and the actinides (such as actinium and plutonium). Some people don’t include the superheavy elements from meitnerium (atomic number 109) to oganesson (atomic number 118) because too few atoms have been synthesized to verify their properties and because these properties are heavily influenced by relativistic effects. Sometimes the element hydrogen (atomic number 1) is excluded as a main group element.

### Other Main Group Elements

Some scientists believe the group 12 elements (zinc, cadmium, and mercury) should be included as main group elements because they share common properties with the elements to the right of them on the table. A few scientists include the group 3 elements (scandium and yttrium) and sometimes the lanthanides and actinides.

### Main Group Element Properties

Main group element properties depend on whether they are s-block or p-block elements:

#### S-Block Element Properties

• The s-block elements have one oxidation state.
• Their general valence configuration is ns1–2.
• Group 1 elements (alkali metals) have a +1 oxidation state. Group 2 elements (alkaline earth metals) have a +2 oxidation state.
• With the exception of helium, all s-block elements are highly reactive.
• The s-block metals tend to be soft, with low melting and boiling points.
• S-block metals are highly electropositive. They form ionic compounds with nonmetals.
• Most of the s-block elements impart color to a flame.

#### P-Block Element Properties

• The p-block elements are characterized by having multiple oxidation states, often separated by two units. For example, the oxidation states of sulfur are -2, 0, +2, +4 and +6.
• But, oxidation state and other properties depend on the group. The group 17 elements (halogens) have an oxidation state of -1, while the group 18 elements (noble gases) have an oxidation state of 0.
• The general oxidation state of p-block metals is  ns2 np1–6. Their valence electron is in the p orbital.
• P-block elements include nonmetals, metalloids, and metals, so their properties depend on their group.

### Importance of the Main Group Elements

The main group elements are important for a few reasons:

• The main group elements, along with a few light transition metals, are the most abundant elements in the universe and on Earth. They comprise 80% of the Earth’s crust. For this reason, the main group elements are also called the representative elements.
• These elements are critical for supporting life. Biological molecules require main group elements, particularly carbon, oxygen, hydrogen, nitrogen, sulfur, and phosphorus.
• The main group elements and their compounds are among the most economically important elements. The majority of manufactured products contain these elements.

### References

• IUPAC (2004). Nomenclature of Inorganic Chemistry.
• Jensen, William B. (2003). “The Place of Zinc, Cadmium, and Mercury in the Periodic Table”. Journal of Chemical Education. 80 (8): 952. doi:10.1021/ed080p952
• King, R. Bruce (1995). Inorganic Chemistry of Main Group Elements. Wiley-VCH. ISBN 0-471-18602-3.

### Related Posts

Sours: https://sciencenotes.org/main-group-elements-definition-and-importance/

It is fair to say that main group elements are not the most glamorous members of the periodic table. The s-block metals such as calcium, and p-block elements like boron and germanium, are literally outshone by their flashier transition metal neighbours gold, palladium and rhodium. Even in pure chemistry terms, the reactivity of main group elements has always seemed a little staid compared to the virtuoso catalytic tricks that many transition metals routinely perform. As early as the 1970s, it seemed that the main group elements had already given up all their secrets, leaving future generations of researchers with little new to find.

‘Within inorganic chemistry, main group was the most boring part of my undergraduate degree,’ recalls Cameron Jones, a researcher at Monash University in Melbourne, Australia, who completed his degree at the University of Western Australia in 1984. ‘At that time, it was thought that everything we needed to know about the chemistry of the main group elements was known: the properties, oxidation states and reactivity were pretty well developed and there were no new areas to go,’ he says. Transition metal chemistry, in comparison, was undergoing a period of explosive growth that is still to let up.

But at the same time as Jones was learning the dry conventions of classical main group chemistry, the first signs of a renaissance in the field had already begun to appear in the literature. In the early 1980s it was discovered that p-block elements such as silicon and phosphorus could be forced into exotic states of existence – low oxidation and low coordination states – within compounds that were perfectly stable at room temperature. Although potential applications would have been far from the minds of the chemists first discovering this wild new frontier of main group compounds, more recent work suggests that their chemistry has a richness – and a usefulness – to rival that of the transition metals that have long overshadowed them. And Jones is among those researchers currently at the forefront of the resurgence.

1981 is regarded as the turning point, Jones says. In that year, three disruptive discoveries were published that began to break apart the main group chemistry orthodoxy – starting with the so-called double bond rule, which stated that only the lightest members of the periodic table would form stable double bonds. Robert West at the University of Wisconsin–Madison in the US, and his colleagues were the first rule-breakers, creating the earliest example of a stable compound incorporating a silicon–silicon double bond, the equivalent of an alkene in organic chemistry.1

Soon after, Masaaki Yoshifuji at the University of Tokyo in Japan and his team made the first phosphorus–phosphorus double bond.2 And in the same year, Gerd Becker and his co-workers at the University of Stuttgart, Germany, synthesised a compound incorporating a phosphorous–carbon triple bond.3 In the latter compound, the phosphorus was not just in a low oxidation state, it was also one-coordinate, hinting at a future in which main group elements with vacant coordination sites might act as catalytic centres able to capture substrates for catalysis.

### Bulking up

The key to this breakthrough was ligand design. These three compounds are united in their use of bulky substituents to stabilise the main group element in question in a state that would otherwise be too unstable. ‘Steric bulk allows kinetic stabilisation of low coordinate and low oxidation state systems,’ explains Jones. ‘It hinders them from reacting with oxygen or water, or undergoing disproportionation processes [which would return the element to its more usual oxidation states]’. West’s disilene, for example, featured a total of four bulky, benzene-based ligands called mesityl groups, whereas Yoshifuji used two even bulkier tri-tert-butylphenyl groups to create his diphosphene.

As bulky ligand design allowed more and more stable examples of main group elements with low oxidation state or coordination number, increasing numbers of researchers began to join the field. ‘It probably wasn’t until the turn of the millennium that it really took off – now it seems that nearly every Nature Chemistry or Science issue has got something on it,’ Jones says.

The examples of stable compounds featuring main group elements in states once thought impossible continue to roll in. Not so long ago, stable acyclic silylenes – the silicon equivalent of a carbene, a highly reactive species that is only two-coordinate and which features an electron lone pair on the silicon – were unheard of. In 2012, Jones and his collaborators at the University of Oxford and University College London in the UK published the first example, stabilised by a bulky boron-based ligand.4 ‘It actually ties in nicely with West’s first disilylene,’ he says. ‘The way he made it was to start with a [conventional] silicon(iv) compound and photolyse it. He suggested that he made a silylene intermediate, which was a deep blue colour, stable only below 77K, and then that dimerised to give the silicon–silicon double bond.’

Like Jones, Matthias Driess was still a student when the pioneering work of West and Yoshifuji was published. ‘Their breakthrough, demonstrating that you could isolate these compounds, put them in a bottle and study their reactivity – at this stage I was fascinated,’ he recalls. Driess now works as a researcher in this area at the Technical University of Berlin in Germany – an area undergoing a shift from simply making these new compounds to trying to put them to use. ‘After people had hunted new species, they asked themselves “What can we do with them?”’ he says. ‘After a certain time playing around with new systems, once you recognise what they can do, you would like to use them for the benefit of mankind. For main group chemistry, this has just started.’

The development that pointed to a way that low oxidation state main group compounds could be put to use was the realisation around the middle of the last decade that they are capable of activating small molecules – such as hydrocarbons, dihydrogen and carbon dioxide. ‘The dream is to use non-metals as catalysts for the important transformations of small molecules that we all rely on,’ Driess says.

### Move over, metal

Why go to the trouble of developing main group-based catalysts? Transition metals are the well-established masters of catalysis chemistry, and new facets to their reactivity continue to be unearthed. But they also have a drawback, points out Doug Stephan, a researcher in main group catalysis at the University of Toronto in Canada who has perhaps pushed main group catalysis the closest toward synthetic utility (see box). The most active transition metal catalysts tend to be the expensive precious metals, such as rhodium, palladium and platinum. These metals are also considered toxic, which causes a problem when they are used to synthesise pharmaceuticals, for example. ‘One of the biggest costs associated with the production of drugs these days is the removal of transition metals,’ Stephan says. Switching to main group catalysts would ease this problem, he says – and boron or silicon, say, are also significantly cheaper than any precious metal. Other transition metals such as iron or nickel also hold this appeal, he admits – the main group systems simply offer another alternative.

Driess’s dream of metal-free catalysis is one shared with many others in the field, Jones included. ‘People are looking more and more at the reactivity, and these are very reactive systems – that, I think, is the next stage of the renaissance of main group chemistry,’ he says. Jones’s recent publication revealing the first acyclic silylene, for example, also showed that the compound would activate dihydrogen even below room temperature – the first silicon compound shown to do so.

Using a main group compound to activate dihydrogen – breaking the hydrogen–hydrogen bond in an oxidative addition process, so that the two hydrogen atoms both end up covalently bonded to the silicon atom – was first achieved by Phil Power and his team at the University of California, Davis in the US. Power used a digermyne, the germanium equivalent of an alkyne.5 The process may sound trivial, but is in fact no small achievement. ‘Dihydrogen is the smallest molecule you can think of but with the strongest covalent bond between two homoelements,’ Driess says.

Whether main group or transition metal, an element needs several key features to be able to pull dihydrogen apart in this way. ‘The centre needs a vacant coordination site – an empty orbital into which to suck up the electrons of the dihydrogen,’ says Driess. To do that effectively, the energy of this orbital (the lowest unoccupied molecular orbital, or LUMO) must fairly closely match that of the dihydrogen donor orbital (its highest occupied molecular orbital, or HOMO). ‘That’s what transition metals beautifully fulfil – a vacant coordination site, and a LUMO that matches the energy of the HOMO of the dihydrogen molecule,’ says Driess. ‘But that is also the beauty of some main group low coordinate compounds,’ he adds. ‘Today we have a lot of examples of silicon compounds with a vacant coordination site – now we have to learn how to tune the electron level, the LUMO acceptor level. We are just at the stage where we can show that this is really possible.’

As with West and Yoshifuji’s work, the key to accessing these new compounds is all in the ligand design. Steric bulk is a prerequisite – but too bulky and the incoming dihydrogen molecule will not be able to access the central silicon atom. Similarly, the ligand’s chemical make-up influences orbital energy levels. ‘At the moment, some of the best ligands we have are nitrogen-chelating ligands called beta diketaminatyl ligands,’ says Driess. ‘And then we have carbenes. I think these are the star ligands at the moment; the N -heterocyclic carbene ligand is really one of the breakthroughs in main group chemistry.’

As an example, Driess points to the work of Guy Bertrand at the University of California San Diego in the US, who has been making boron compounds in which the central boron atom is flanked on each side by a N-heterocyclic carbene (NHC).6 Boron is typically a quintessential Lewis acid: an atom blessed with only three electrons in the neutral state, it is a long way short of the eight needed for maximum stability, and so is known as an excellent electron acceptor. However, NHCs are such powerful electron donors that the boron atom itself switches behaviour to become electron-donating. ‘It’s turning the world upside down,’ says Stephan, whose eye has also been caught by the work. ‘It’s taking a Lewis acid and turning it into a Lewis base. It’s fundamental research at this stage, but terrifically exciting,’ he adds.

### Learning to cycle

Although developing low-valent main group compounds that can successfully coordinate small molecules such as dihydrogen has now been achieved, this step is just the first in a sequence of reactions that must be developed if Driess’s dream of turning main group compounds into useful catalysts is to be realised.  Activating dihydrogen, for example, could be the first step in a hydrogenation process to catalytically convert an alkene into an alkane by adding dihydrogen across the carbon–carbon double bond. In a hydrogenation reaction catalysed by transition metals, the step after oxidative addition of dihydrogen would be the coordination of the alkene substrate, to which the hydrogen atoms transfer, before that cleaves off to regenerate the original metal centre and the process begins again.

But to get such a cycle to work, several traps must be avoided. ‘For the low coordination number main group compounds, if you activate the dihydrogen but the formed element–hydrogen bond is too strong, or if there is no more vacant coordination site for the second substrate, then this is a dead end,’ says Driess. Navigating through this tricky territory to put all the steps in place for a full catalytic cycle remains work in progress.

‘It is still being shown that low oxidation state p-block compounds can participate in the kind of reactions usually only associated with transition metals,’ adds Jones. ‘Real catalysis is yet to be achieved but I think certainly do-able, and within the next few years we’ll see some true catalysis coming out, especially from the group 14 elements silicon and germanium.’

Driess is even more bullish about the area’s prospects: ‘I would expect that in another 10 years, low valent main group compounds will be as good as traditional transition metal compounds for activating small molecules.’ As a researcher also known for his ground-breaking transition metal catalysis research, he is certainly well placed to judge.

James Mitchell Crow is a science writer based in Melbourne, Australia

### The FLP side

The area of main group chemistry closest to being ‘marketable’ for use in an industrial situation for organic synthesis is that of frustrated Lewis pairs (FLPs), says Jones.

FLPs were a discovery made by Doug Stephan and his team at University of Toronto in Canada in 2006.7 ‘We were looking at titanium-based olefin polymerisation catalysts, using boron reagents as activators, stabilising some very active polymerisation catalysts with phosphine donors,’ Stephan recalls. ‘Going through a series of reactions, we discovered that very bulky phosphines did something quite different – they didn’t react with titanium, but just with the boron centre.’

Stephan discovered that he had made a particularly unlikely-sounding compound: one that would react with dihydrogen to incorporate both a proton (H+) and a hydride ion (H), the former located at the phosphorus atom and the latter at the boron. This kind of compound sounds exactly like it should spontaneously lose dihydrogen, not take it up. Key to this behaviour is the use of bulky ligands in the parent boron and phosphorus compounds, thereby preventing the proton and hydride ion from recombining to form dihydrogen at room temperature. ‘Once you’ve activated hydrogen, the obvious next step is to use it in hydrogenation catalysis, so that’s what we did over the last few years,’ Stephan says. The team has successfully hydrogenated imines and alkenes in this way,  and has now moved on to catalytic reactions involving activating carbon dioxide, a feedstock in no short supply.

‘Our first attempt was simply to capture carbon dioxide with FLPs. Then we found that if we moved to stoichiometric aluminium phosphorus we could get stoichiometric reduction to go, reducing carbon dioxide to carbon monoxide, and also carbon dioxide to methanol. Then the next evolution was to try to get a catalytic system,’ Stephan says. The process worked, but generated a troublesome by-product, phosphine oxide, in the process. ‘We need another oxygen acceptor that would be more valuable than phosphine oxide,’ Stephan summarises. ‘That work’s ongoing, but the good news is we can do catalysis without using precious metals.’

### References

1 R West, M J Fink and J Michl, Science, 1981, 214, 1343 (DOI: 10.1126/science.214.4527.1343)

2 M Yoshifuji et al, J. Am. Chem. Soc., 1981, 103, 4587 (DOI: 10.1021/ja00405a054)

3 G Becker, G Gresser and W Z Uhl, Z. Naturforsch. B, 1981, 36, 16

4 A V Protchenko et al, J. Am. Chem. Soc., 2012, 134, 6500 (DOI: 10.1021/ja301042u)

5 G H Spikes, J C Fettinger and P P Power, J. Am. Chem. Soc., 2005, 127, 12232 (DOI: 10.1021/ja053247a)

6 R Kinjo et al, Science, 2011, 333, 610 (DOI: 10.1126/science.1207573)

7 D W  Stephan, Org. Biomol. Chem., 2012, 10, 5740 (DOI: 10.1039/c2ob25339a)

Sours: https://www.chemistryworld.com/features/main-group-renaissance/6230.article

## Main Group Elements Definition

In chemistry and physics, the main group elements are any of the chemical elements belonging to the s and p blocks of the periodic table. The s-block elements are group 1 (alkali metals) and group 2 (alkaline earth metals). The p-block elements are groups 13-18 (basic metals, metalloids, nonmetals, halogens, and noble gases). The s-block elements usually have one oxidation state (+1 for group 1 and +2 for group 2). The p-block elements may have more than one oxidation state, but when this happens, the most common oxidation states are separated by two units. Specific examples of main group elements include helium, lithium, boron, carbon, nitrogen, oxygen, fluorine, and neon.

### Significance of the Main Group Elements

The main group elements, along with a few light transition metals, are the most abundant elements in the universe, solar system, and on Earth. For this reason, main group elements are sometimes known as representative elements.

### Elements That Aren't in the Main Group

Traditionally, the d-block elements have not been considered to be main group elements. In other words, the transition metals in the middle of the periodic table and the lanthanides and actinides below the main body of the table are not main group elements. Some scientists do not include hydrogen as a main group element.

Some scientists believe zinc, cadmium, and mercury should be included as main group elements. Others believe group 3 elements should be added to the group. Arguments may be made for including the lanthanides and actinides, based on their oxidation states.

### Sources

• King, R. Bruce (1995). Inorganic Chemistry of Main Group Elements. Wiley-VCH. ISBN 0-471-18602-3.
• "Nomenclature of Inorganic Chemistry". (2014) International Union of Pure and Applied Chemistry.
Sours: https://www.thoughtco.com/definition-of-main-group-elements-605876
Counting valence electrons for main group elements - Periodic table - Chemistry - Khan Academy

## Book: Chemistry of the Main Group Elements (Barron)

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• The main group (s- and p-block) elements are among the most diverse in the Periodic Table. Ranging from non-metallic gases (e.g., hydrogen and fluorine), through semi-metals (e.g., metalloids such as silicon) to highly reactive metals (e.g., sodium and potassium). The study of the main group elements is important for a number of reasons. On an academic level they exemplify the trends and predictions in structure and reactivity that are the key to the Periodic Table. They represent the diversity of inorganic chemistry, and the fundamental aspects of structure and bonding that are also present for the transition metal, lanthanide and actinide elements.

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Sours: https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Book%3A_Chemistry_of_the_Main_Group_Elements_(Barron)

### Learning Objectives

By the end of this section, you will be able to:

• State the periodic law and explain the organization of elements in the periodic table
• Predict the general properties of elements based on their location within the periodic table
• Identify metals, nonmetals, and metalloids by their properties and/or location on the periodic table

As early chemists worked to purify ores and discovered more elements, they realized that various elements could be grouped together by their similar chemical behaviors. One such grouping includes lithium (Li), sodium (Na), and potassium (K): These elements all are shiny, conduct heat and electricity well, and have similar chemical properties. A second grouping includes calcium (Ca), strontium (Sr), and barium (Ba), which also are shiny, good conductors of heat and electricity, and have chemical properties in common. However, the specific properties of these two groupings are notably different from each other. For example: Li, Na, and K are much more reactive than are Ca, Sr, and Ba; Li, Na, and K form compounds with oxygen in a ratio of two of their atoms to one oxygen atom, whereas Ca, Sr, and Ba form compounds with one of their atoms to one oxygen atom. Fluorine (F), chlorine (Cl), bromine (Br), and iodine (I) also exhibit similar properties to each other, but these properties are drastically different from those of any of the elements above.

Dimitri Mendeleev in Russia (1869) and Lothar Meyer in Germany (1870) independently recognized that there was a periodic relationship among the properties of the elements known at that time. Both published tables with the elements arranged according to increasing atomic mass. But Mendeleev went one step further than Meyer: He used his table to predict the existence of elements that would have the properties similar to aluminum and silicon, but were yet unknown. The discoveries of gallium (1875) and germanium (1886) provided great support for Mendeleev’s work. Although Mendeleev and Meyer had a long dispute over priority, Mendeleev’s contributions to the development of the periodic table are now more widely recognized (Figure 1).

Figure 1. (a) Dimitri Mendeleev is widely credited with creating (b) the first periodic table of the elements. (credit a: modification of work by Serge Lachinov; credit b: modification of work by “Den fjättrade ankan”/Wikimedia Commons)

By the twentieth century, it became apparent that the periodic relationship involved atomic numbers rather than atomic masses. The modern statement of this relationship, the periodic law, is as follows: the properties of the elements are periodic functions of their atomic numbers. A modern periodic table arranges the elements in increasing order of their atomic numbers and groups atoms with similar properties in the same vertical column (Figure 2). Each box represents an element and contains its atomic number, symbol, average atomic mass, and (sometimes) name. The elements are arranged in seven horizontal rows, called periods or series, and 18 vertical columns, called groups. Groups are labeled at the top of each column. In the United States, the labels traditionally were numerals with capital letters. However, IUPAC recommends that the numbers 1 through 18 be used, and these labels are more common. For the table to fit on a single page, parts of two of the rows, a total of 14 columns, are usually written below the main body of the table.

Figure 2. Elements in the periodic table are organized according to their properties.

Many elements differ dramatically in their chemical and physical properties, but some elements are similar in their behaviors. For example, many elements appear shiny, are malleable (able to be deformed without breaking) and ductile (can be drawn into wires), and conduct heat and electricity well. Other elements are not shiny, malleable, or ductile, and are poor conductors of heat and electricity. We can sort the elements into large classes with common properties: metals (elements that are shiny, malleable, good conductors of heat and electricity—shaded yellow); nonmetals (elements that appear dull, poor conductors of heat and electricity—shaded green); and metalloids (elements that conduct heat and electricity moderately well, and possess some properties of metals and some properties of nonmetals—shaded purple).

The elements can also be classified into the main-group elements (or representative elements) in the columns labeled 1, 2, and 13–18; the transition metals in the columns labeled 3–12; and inner transition metals in the two rows at the bottom of the table (the top-row elements are called lanthanides and the bottom-row elements are actinides; Figure 3). The elements can be subdivided further by more specific properties, such as the composition of the compounds they form. For example, the elements in group 1 (the first column) form compounds that consist of one atom of the element and one atom of hydrogen. These elements (except hydrogen) are known as alkali metals, and they all have similar chemical properties. The elements in group 2 (the second column) form compounds consisting of one atom of the element and two atoms of hydrogen: These are called alkaline earth metals, with similar properties among members of that group. Other groups with specific names are the pnictogens (group 15), chalcogens (group 16), halogens (group 17), and the noble gases (group 18, also known as inert gases). The groups can also be referred to by the first element of the group: For example, the chalcogens can be called the oxygen group or oxygen family. Hydrogen is a unique, nonmetallic element with properties similar to both group 1A and group 7A elements. For that reason, hydrogen may be shown at the top of both groups, or by itself.

Figure 3. The periodic table organizes elements with similar properties into groups.

Click on this link to the Royal Society of Chemistry for an interactive periodic table, which you can use to explore the properties of the elements (includes podcasts and videos of each element). You may also want to try this one from PeriodicTable.com that shows photos of all the elements.

### Example 1: Naming Groups of Elements

Atoms of each of the following elements are essential for life. Give the group name for the following elements:

1. chlorine
2. calcium
3. sodium
4. sulfur
The family names are as follows:
1. halogen
2. alkaline earth metal
3. alkali metal
4. chalcogen

Give the group name for each of the following elements:

1. krypton
2. selenium
3. barium
4. lithium
1. noble gas
2. chalcogen
3. alkaline earth metal
4. alkali metal

In studying the periodic table, you might have noticed something about the atomic masses of some of the elements. Element 43 (technetium), element 61 (promethium), and most of the elements with atomic number 84 (polonium) and higher have their atomic mass given in square brackets. This is done for elements that consist entirely of unstable, radioactive isotopes (you will learn more about radioactivity in the nuclear chemistry chapter). An average atomic weight cannot be determined for these elements because their radioisotopes may vary significantly in relative abundance, depending on the source, or may not even exist in nature. The number in square brackets is the atomic mass number (and approximate atomic mass) of the most stable isotope of that element.

### Key Concepts and Summary

The discovery of the periodic recurrence of similar properties among the elements led to the formulation of the periodic table, in which the elements are arranged in order of increasing atomic number in rows known as periods and columns known as groups. Elements in the same group of the periodic table have similar chemical properties. Elements can be classified as metals, metalloids, and nonmetals, or as a main-group elements, transition metals, and inner transition metals. Groups are numbered 1–18 from left to right. The elements in group 1 are known as the alkali metals; those in group 2 are the alkaline earth metals; those in 15 are the pnictogens; those in 16 are the chalcogens; those in 17 are the halogens; and those in 18 are the noble gases.

### Exercises

#### Metal or Nonmetal?

1. Using the periodic table, classify each of the following elements as a metal or a nonmetal, and then further classify each as a main-group (representative) element, transition metal, or inner transition metal:
1. uranium
2. bromine
3. strontium
4. neon
5. gold
6. americium
7. rhodium
8. sulfur
9. carbon
10. potassium
2. Using the periodic table, classify each of the following elements as a metal or a nonmetal, and then further classify each as a main-group (representative) element, transition metal, or inner transition metal:
1. cobalt
2. europium
3. iodine
4. indium
5. lithium
6. oxygen
8. terbium
9. rhenium

1. (a) metal, inner transition metal; (b) nonmetal, representative element; (c) metal, representative element; (d) nonmetal, representative element; (e) metal, transition metal; (f) metal, inner transition metal; (g) metal, transition metal; (h) nonmetal, representative element; (i) nonmetal, representative element; (j) metal, representative element

#### Identifying Elements

1. Using the periodic table, identify the lightest member of each of the following groups:
1. noble gases
2. alkaline earth metals
3. alkali metals
4. chalcogens
2. Using the periodic table, identify the heaviest member of each of the following groups:
1. alkali metals
2. chalcogens
3. noble gases
4. alkaline earth metals
3. Use the periodic table to give the name and symbol for each of the following elements:
1. the noble gas in the same period as germanium
2. the alkaline earth metal in the same period as selenium
3. the halogen in the same period as lithium
4. the chalcogen in the same period as cadmium
4. Use the periodic table to give the name and symbol for each of the following elements:
1. the halogen in the same period as the alkali metal with 11 protons
2. the alkaline earth metal in the same period with the neutral noble gas with 18 electrons
3. the noble gas in the same row as an isotope with 30 neutrons and 25 protons
4. the noble gas in the same period as gold
5. Write a symbol for each of the following neutral isotopes. Include the atomic number and mass number for each.
1. the alkali metal with 11 protons and a mass number of 23
2. the noble gas element with and 75 neutrons in its nucleus and 54 electrons in the neutral atom
3. the isotope with 33 protons and 40 neutrons in its nucleus
4. the alkaline earth metal with 88 electrons and 138 neutrons
6. Write a symbol for each of the following neutral isotopes. Include the atomic number and mass number for each.
1. the chalcogen with a mass number of 125
2. the halogen whose longest-lived isotope is radioactive
3. the noble gas, used in lighting, with 10 electrons and 10 neutrons
4. the lightest alkali metal with three neutrons

1. (a) He; (b) Be; (c) Li; (d) O

3. (a) krypton, Kr; (b) calcium, Ca; (c) fluorine, F; (d) tellurium, Te

5. (a) ${}_{11}^{23}\text{Na}$ ; (b) ${}_{54}^{129}\text{Xe}$ ; (c) ${}_{33}^{73}\text{As}$ ; (d) ${}_{88}^{226}\text{Ra}$

### Glossary

actinide: inner transition metal in the bottom of the bottom two rows of the periodic table

alkali metal: element in group 1

alkaline earth metal: element in group 2

chalcogen: element in group 16

group: vertical column of the periodic table

halogen: element in group 17

inert gas: (also, noble gas) element in group 18

inner transition metal: (also, lanthanide or actinide) element in the bottom two rows; if in the first row, also called lanthanide, of if in the second row, also called actinide

lanthanide: inner transition metal in the top of the bottom two rows of the periodic table

main-group element: (also, representative element) element in columns 1, 2, and 12–18

metal: element that is shiny, malleable, good conductor of heat and electricity

metalloid: element that conducts heat and electricity moderately well, and possesses some properties of metals and some properties of nonmetals

noble gas: (also, inert gas) element in group 18

nonmetal: element that appears dull, poor conductor of heat and electricity

period: (also, series) horizontal row of the period table

periodic law: properties of the elements are periodic function of their atomic numbers.

periodic table: table of the elements that places elements with similar chemical properties close together

pnictogen: element in group 15

representative element: (also, main-group element) element in columns 1, 2, and 12–18

series: (also, period) horizontal row of the period table

transition metal: element in columns 3–11

Sours: https://courses.lumenlearning.com/sanjacinto-atdcoursereview-genchemistry1-1/chapter/the-periodic-table/

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