Blocks of the periodic table

s, p, d and f: what puts an element in each region

1. The transition elements and their series

2. Four coloured regions

The long form of the periodic table has four coloured regions. What puts an element in one region and not another?

Element table

The long form of the periodic table, coloured by block

Pick the right answer

Predict: what decides an element's region?

A. Its atomic mass
B. The type of sublevel that receives its last electron
C. Whether it is a metal or a nonmetal

Explanation

An element's block is set by the type of sublevel that receives its last electron: s, p, d or f.

3. Blocks follow the last electron

block

A region of the table whose elements get their last electron in the same type of sublevel.

Sodium ends with

3s¹ 3 s^{1}

, so it is in the s-block. Chlorine ends with

3p⁵ 3 p^{5}

, so it is in the p-block.

Element table

s-block, p-block

Cl: 3p⁵
Na: 3s¹

The s-block (left) and the p-block (right)

The width fits the sublevel. s holds 2 electrons, so the s-block has 2 columns. p holds 6, so 6 columns.

4. Groups of the s- and p-blocks

The s- and p-blocks sit on both sides of the long form of the table. They hold the representative elements (groups IA to VIIA) and the noble gases (group 0).

Block	Group	Group number	Outer electrons end with
s	IA	1	$ns¹ n s^{1}$
s	IIA	2	$ns² n s^{2}$
p	IIIA	13	$ns²\ np¹$
p	IVA	14	$ns²\ np²$
p	VA	15	$ns²\ np³$
p	VIA	16	$ns²\ np⁴$
p	VIIA	17	$ns²\ np⁵$
p	0 (noble gases)	18	$ns²\ np⁶$ (He: $1s² 1 s^{2}$ )

Groups of the s- and p-blocks (n = the period number)

Notice: for groups IA to VIIA, the Roman numeral counts the electrons in the outer level. The middle columns get different labels, which you'll meet in Chapter 1.

5. Find the block

Sort into groups

Sort each element by its block. First find the sublevel that receives the last electron.

$₁₂Mg X_{12} X_{212}^{2} Mg$ : $[Ne]\ 3s²$ $₁₉K X_{19} X_{219}^{2} K$ : $[Ar]\ 4s¹$ $₇N X_{7} X_{27}^{2} N$ : $1s²\ 2s²\ 2p³$ $₃₅Br X_{35} X_{235}^{2} Br$ : $[Ar]\ 4s²\ 3d¹⁰\ 4p⁵$ $₂₆Fe X_{26} X_{226}^{2} Fe$ : $[Ar]\ 4s²\ 3d⁶$ $₄₀Zr X_{40} X_{240}^{2} Zr$ : $[Kr]\ 5s²\ 4d²$

Pick the right answer

Aluminum,

₁₃Al X_{13} X_{213}^{2} Al

, is

[Ne]\ 3s²\ 3p¹

. Which block and group is it in?

A. p-block, group IIIA (13)
B. s-block, group IIA (2)
C. p-block, group IA (1)
D. d-block, group IIIB (3)

Explanation

The last electron of aluminum enters 3p, so it is in the p-block. Its outer level holds 2 + 1 = 3 electrons, so it is in group IIIA (13).

6. Summary

Block = the type of sublevel that receives the last electron.
The s- and p-blocks hold the representative elements (IA to VIIA) and the noble gases (group 0).
The d-block is in the middle; the f-block is the two rows at the bottom.

Can you explain why Na and Cl are in different blocks, though both are in period 3?

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