Metals, Nonmetals and Metalloids

Think of a copper wire, a lump of charcoal and the silicon chip inside a calculator. Copper shines, bends without breaking and carries electric current easily. Charcoal is dull, crumbles when you press it and hardly carries current at all. Silicon sits in between: it shines like a metal but carries only a little current. These three materials stand for the three families into which all elements are sorted.

The property used for this sorting is metallic character: how strongly an element behaves like a metal. On this basis, elements are classified into three groups: metals, nonmetals and metalloids. The modern periodic table gives each of them its own region, so knowing where an element sits already tells you a great deal about it.

Metals are placed on the left side and across the broad middle of the modern periodic table. All the elements of groups IA, IIA and IIIA are metals, except boron in group IIIA. Sodium, magnesium and aluminium are familiar metals from these groups.

Metals are good conductors of heat and electricity. That is why cooking pots are made of aluminium or steel and electric wires are made of copper or aluminium. Metals are not all equally reactive, though. The metals of group IA react most readily, and the metals of groups IIA and IIIA are less reactive than them.

Between group IIA and group IIIA lies a wide block of ten columns, labelled group IIIB to group IIB. The elements here are metals too. Iron (Fe), cobalt (Co), nickel (Ni), silver (Ag), gold (Au), mercury (Hg) and zinc (Zn) are examples. They are far less reactive than the metals of groups IA and IIA. Sodium reacts violently the moment it touches water, but gold stays bright for centuries and iron only rusts slowly.

Elements with one electron in their outermost shell are placed in group IA. Lithium (Li), sodium (Na) and potassium (K) belong here. That single outer electron leaves easily, which makes these metals highly reactive. When they dissolve in water they form a strong base, also called an alkali. Sodium, for example, gives sodium hydroxide, a strong alkali. This is where their name comes from.

Their valence shell electronic configuration is \( ns^1 \). Here n stands for the number of the outermost shell, and the 1 written above tells us there is one electron in the s subshell of that shell. Sodium, with atomic number 11, shows the pattern:

\[ \text{Na}: 1s^2,\ 2s^2\,2p^6,\ 3s^1 \]

Sodium's outermost shell is the third, so here n = 3 and the configuration ends in \( 3s^1 \). The alkali metals are soft, so soft that sodium can be cut with a knife. They also have low density; lithium, sodium and potassium all float on water.

Elements with two electrons in their outermost shell are placed in group IIA. Magnesium (Mg) and calcium (Ca) are the best known members. Their valence shell electronic configuration is \( ns^2 \). Magnesium, with atomic number 12, has:

\[ \text{Mg}: 1s^2,\ 2s^2\,2p^6,\ 3s^2 \]

The oxides of these metals are soluble in water, giving alkaline solutions, and the metals are found on the earth's surface, in rocks such as limestone and in soil. Those two facts together give the group its name. They react less vigorously than the alkali metals.

Nonmetals are kept on the right side of the periodic table. The elements of groups VA, VIA and VIIA, together with group VIIIA, also called group 18 or group 0, are nonmetals. Nitrogen, oxygen, chlorine and neon are examples. Carbon, at the top of group IVA, and hydrogen are nonmetals as well. Most nonmetals are gases or brittle solids; they have no metallic shine and conduct heat and electricity poorly.

Elements with seven electrons in their valence shell are kept in group VIIA, which is group 17. Fluorine (F), chlorine (Cl), bromine (Br) and iodine (I) belong here. Seven is one short of eight, so these elements readily gain one electron from other elements to fill their valence shell with eight electrons. This makes them very reactive. They are the most reactive nonmetals.

Their outermost electronic configuration is \( ns^2\,np^5 \). Chlorine, with atomic number 17, shows it clearly:

\[ \text{Cl}: 1s^2,\ 2s^2\,2p^6,\ 3s^2\,3p^5 \]

Two electrons in 3s and five in 3p make seven valence electrons. The halogens have low density. The word halogen means salt maker: chlorine joined with sodium makes common salt, sodium chloride.

Group 0, also called group VIIIA or 18, holds helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Rn). Apart from helium, each has eight electrons in its valence shell. Helium has just two electrons, both in its first shell, and that first shell is also its valence shell. Two is the most the first shell can hold, so helium's shell is full too.

Their valence shell electronic configuration is written \( ns^2\,np^6 \). Argon, with atomic number 18, has:

\[ \text{Ar}: 1s^2,\ 2s^2\,2p^6,\ 3s^2\,3p^6 \]

With a complete octet in the valence shell, these elements have nothing to gain or lose, so they do not take part in chemical reactions. That is why they are called inert gases, and also noble gases. Argon is filled into electric bulbs because it will not react even with the hot filament.

Between the metals and the nonmetals runs a narrow, stepped band of elements called metalloids. They show some properties like metals and some like nonmetals. Silicon, for instance, has a shiny grey surface like a metal but is brittle and shatters like a nonmetal. Silicon (Si), germanium (Ge) and bismuth (Bi) are metalloids. Boron, the one element of group IIIA that is not a metal, is also a metalloid.

Metalloids are poor conductors of electricity, and are called semiconductors. Their electrical conductivity is less than that of metals and more than that of nonmetals. This in-between behaviour is exactly what makes silicon and germanium so useful: computer chips, mobile phones and solar panels all depend on semiconductors made from them.

All the groups above follow one pattern: the number of electrons in the valence shell decides an element's family. So if you can write an element's electronic configuration, you can place it in the table. In the atoms below, sodium has one electron in its outer shell, magnesium two, chlorine seven and argon eight.

Worked example 1: Which family does potassium, atomic number 19, belong to?

Step 1: Filling 19 electrons into the subshells in increasing order of energy. Since 4s has lower energy than 3d, the last electron goes into 4s:

\[ 1s^2,\ 2s^2\,2p^6,\ 3s^2\,3p^6,\ 4s^1 \]

Step 2: Picking out the outermost shell, which is the fourth shell (n = 4):

\[ 4s^1 \]

Step 3: Matching this against the general pattern of group IA:

\[ ns^1 \rightarrow 4s^1 \]

Conclusion: potassium has one electron in its valence shell, so it is an alkali metal of group IA.

Worked example 2: Which family does fluorine, atomic number 9, belong to?

Step 1: Filling 9 electrons into the subshells in order:

\[ 1s^2,\ 2s^2\,2p^5 \]

Step 2: Adding the electrons of the outermost shell, the second shell (n = 2), in 2s and 2p:

\[ 2 + 5 = 7 \]

Step 3: Matching this against the general pattern of the halogens:

\[ ns^2\,np^5 \rightarrow 2s^2\,2p^5 \]

Conclusion: fluorine has seven electrons in its valence shell, so it is a halogen of group VIIA and a nonmetal.