Chemistry, Third edition

194 12 · CHEMICAL FAMILIES

An older numbering system for the groups is also shown on the Periodic Table,

whereby Groups 13, 14, 15, 16, 17 and 18 are shown as Groups 3, 4, 5, 6, 7 and 0,

respectively. This system does not number the block of elements known as the

d-block elements (transition elements).

Other points to note about the Periodic Table:

●The block of elements between Groups 2 and 13 is named the d-block elementsor

transition elements.

●The horizontal rows in the table are called periods. Period I consists only of the

two elements H and He. Period 2 consists of the elements Li, Be, B, C, N, O, F and

Ne. The zigzag line in the table separates the metals from the non-metals. The

metals are on the left and you can see that there are a great deal many more metals

in the table than non-metals.

●Hydrogen does not really belong in any group of the table, so it is usually placed at

the top, on its own.

In order that the Periodic Table should fit on a single page, the lanthanoids(ele-

ments 57–70) and actinoids(elements 89–102) series are usually written below the

table. We will not concern ourselves with the chemistry of these elements in this book.

After completing Exercise 12A, you should have gained a valuable clue as to why

elements in the same group often have similar physical and chemical properties:

All the elements in a given group have the same number of electrons in the

outermost shell of their atoms.

Since the type of bonding in compounds of an element is dependent on its ioniza-

tion energy, which is related to the number of electrons in the outermost shell of its

atoms, then we might expect those elements with similar electronic configurations to

exhibit similar properties. Although this is generally true of the elements in a group,

there are gradations (gradual changes) of the properties of the elements within a group.

If you write the electronic configuration of the elements in s,p,d,f notation, you

should be able to see that:

●Group 1 and Group 2 elements are often called the s-block elementsbecause they

have s-orbital electrons in the outermost shell of their atoms.

●Groups 13 to 18 elements are called the p-block elementsbecause they have

p-orbital electrons in the outermost shell of their atoms.

●The block of elements betweenGroups 2 and 13 is known as the d-block

elements, because d electrons generally play an important part in determining

their chemistry.

Group 1 elements – the alkali metals:

Li, Na, K, Rb, Cs, Fr

Electronic configuration

These elements have one electron in the outermost shell of their atoms; their chem-

istry is dominated by the tendency to lose this electron and they are good reducing

agents. The general ionic equation for this loss of an electron can be written as

MMe

12.2

Electron

arrangements of

elements in a

group

(i)iAtoms of Li (atomic

number 3) have the

electronic structure 2.1.

Write down the electron

arrangements (Bohr

model and s,p,d,f

structures) for the other

members of Group 1 –

Na, K and Rb. Can you

give a general

expression for the

electron arrangements

of the elements in

Group 1?

(ii)Write down the electronic

structure (Bohr model

and s,p,d,f

arrangements) for the

elements in Group

17 – F, Cl, Br, I. Give a

general expression for

the electron

arrangements of the

elements in this group.

Exercise 12A