Groups, families and blocks

Read the outer shell

The table has eighteen groups. Elements in a group have the same number of electrons in their outer shell, so they behave alike. Each group is also called a family and has a family name.

Table 8.2 gives the outer configuration. Group 1, the alkali metals, end in ns¹; group 2, the alkaline earth metals, in ns². Groups 13 to 18 add p electrons: boron family ns² np¹, carbon ns² np², nitrogen ns² np³, oxygen ns² np⁴, halogens ns² np⁵ and noble gases ns² np⁶.

Groups 1–2 and 13–17 hold the normal elements: their inner shells are full and only the outer shell is incomplete. Groups 3 to 12 are the transition elements, where an inner d subshell is still filling.

The table is also split into blocks named after the subshell being filled. Groups 1 and 2 are the s-block; groups 13 to 18 are the p-block; the d-block sits between them; and the f-block is the two rows at the bottom.

The last subshell being filled names the block: s, p, d or f.

Key terms

Family

Naming groups.

Normal elements

Only the outer shell incomplete.

Transition elements

Inner d subshell filling.

s-block

Outer s subshell filling.

p-block

Outer p subshell filling.

Short questions with model answers

1. Q1. An element's outer shell is s² p³. Find its group and block. (Exercise 1, p. 109)

   • Count outer electrons
   • Block

   Group 15 (nitrogen family), p-block. With 3s² 3p³ it would be period 3 (phosphorus).

2. Q2. What is the group of an element with eight electrons in its outer shell, and what is its physical state? (Exercise 2, p. 109)

   • ns² np⁶
   • State

   Group 18; it is a gas.

Common mistakes

• ✗ A group 15 element has 15 outer electrons.

  ✓ For groups 13–18, outer electrons = group number minus 10 (ns² np³ is 5).

• ✗ Transition metals are normal elements.

  ✓ Normal elements are groups 1–2 and 13–17; groups 3–12 are transition (p. 107).

• ✗ The f-block lies between the s- and p-blocks.

  ✓ The d-block lies between; the f-block is the two rows at the bottom (p. 107).

MCQs

1. 1. The outer configuration of the halogens is:

   1. (a) ns¹
   2. (b) ns² np⁴
   3. (c) ns² np⁵
   4. (d) ns² np⁶
   Show answer

   (c) Table 8.2.

2. 2. Which outer configuration belongs to a transition metal? (Exercise ii, p. 116)

   1. (a) ns² np⁶
   2. (b) (n−1)d ns²
   3. (c) ns² np³
   4. (d) ns² np⁵
   Show answer

   (b) A d subshell is filling (Table 8.2; see the build report for the printed form).

3. 3. Groups 1 and 2 make up the:

   1. (a) s-block
   2. (b) p-block
   3. (c) d-block
   4. (d) f-block
   Show answer

   (a) p. 107.

4. 4. How many groups are in the modern periodic table?

   1. (a) 7
   2. (b) 8
   3. (c) 18
   4. (d) 32
   Show answer

   (c) p. 107.

5. 5. The element in solar cells is in: (Exercise i, p. 116)

   1. (a) Period 3, group 14
   2. (b) Period 2, group 14
   3. (c) Period 3, group 15
   4. (d) Period 3, group 16
   Show answer

   (a) Silicon: 3s² 3p², carbon family.

Quick revision

• 18 groups; a group shares its outer-shell configuration and is called a family.
• Groups 1–2 and 13–17 are normal elements; 3–12 are transition elements.
• s-block: groups 1–2; p-block: 13–18; d-block between; f-block at the bottom.