s- and p-Block Elements

Lesson

Part 1 — the general plan of the s-block and p-block, then groups 1 and 2. This chapter is formative assessment only: it is not part of the annual theory paper, but it is taught here at textbook depth for school tests.

In this lesson you will

Write the valence configurations of the s-block and p-block groups
Explain the trends in atomic radius, ionic radius, ionisation enthalpy, hydration enthalpy and reducing power in groups 1 and 2
Name the flame colours of the alkali and alkaline earth metals and explain why beryllium and magnesium give none
Explain the unique behaviour of lithium and beryllium and the diagonal relationships Li–Mg and Be–Al

Table of the four blocks of the periodic table with groups and valence configurations
Block	Groups	Valence configuration	Examples
s-block	1 and 2	ns¹ and ns²	Sodium, calcium
p-block	13 to 18	ns² np¹ to ns² np⁶	Aluminium, carbon, chlorine
d-block	3 to 12	(n−1)d¹⁻¹⁰ ns¹⁻²	Iron, copper
f-block	Inner transition	(n−2)f¹⁻¹⁴ …	Cerium, uranium

Concept

Valence configurations of the s-block and p-block

The s-block fills an ns subshell; the p-block fills np after ns². Every group has the same valence configuration all the way down, so the properties follow a pattern within the group.

Table of s-block and p-block groups with valence configuration, family name and common ions
Group	Valence configuration	Family name	Common ions
1	ns¹	Alkali metals	M⁺
2	ns²	Alkaline earth metals	M²⁺
13	ns² np¹	Boron family	M³⁺, M⁺
14	ns² np²	Carbon family	M⁴⁺ (covalent), M²⁺
15 to 17	ns² np³ to ns² np⁵	Nitrogen, oxygen, halogen families	Anions
18	ns² np⁶	Noble gases	None (except Xe, Kr compounds)

Concept

Trends down a group: radius and ionisation enthalpy

Down a group each atom has one more shell, so radius rises; the outer electron feels a weaker pull, so ionisation enthalpy falls. A cation is smaller than its atom, because it has lost its outer shell and has the same nuclear charge holding fewer electrons.

Table of atomic radius, ionic radius and first ionisation enthalpy for the alkali metals
Property	Li	Na	K	Rb	Cs
Atomic radius / pm	152	186	227	248	265
M⁺ radius / pm	76	102	138	152	167
IE₁ / kJ mol⁻¹	520	496	419	403	376

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