40. The s -Block Elements. 40.1 Characteristic Properties of the s -Block Elements 40.2 Variation in Properties of the s -Block Elements 40.3 Variation in Properties of the Compounds of the s -Block Elements. The s -Block Elements.
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40 The s-Block Elements 40.1 Characteristic Properties of the s-Block Elements 40.2 Variation in Properties of the s-Block Elements 40.3 Variation in Properties of the Compounds of the s-Block Elements
The s-Block Elements • Elements of Groups IA* (the alkali metals) and IIA* (the alkaline earth metals) • constitute the s-block elements • their outermost shell electrons are in the s orbital • *Note: In the following, Groups IA and IIA are abbreviated as Groups I and II respectively.
The s-Block Elements • The two groups of elements have many similarities • highly reactive metals • strong reducing agents • form ionic compounds with fixed oxidation states of +1 for Group I elements and +2 for Group II elements
40.1 Characteristic Properties of the s-Block Elements (SB p.38) Metallic Character • All Group I elements • silvery solids and tarnish rapidly in air at room temperature and pressure • stored under paraffin oil or in vacuum-sealed ampoules • (to prevent contact with oxygen and water vapour in air)
40.1 Characteristic Properties of the s-Block Elements (SB p.38) Metallic Character • All Group I elements • weakmetallic bonds • only one valence electron per atom delocalized into the electron sea for the formation of metallic bonds • soft and can be cut with a knife easily
40.1 Characteristic Properties of the s-Block Elements (SB p.40) Low Electronegativity • The outermost shell electrons • effectively shielded from the nucleus by the fully-filled inner electron shells • the outermost shell electrons are only loosely held by the nucleus
40.1 Characteristic Properties of the s-Block Elements (SB p.40) Low Electronegativity • Going down both Groups I and II • the elements become more electropositive • the atoms tend to lose electrons more readily • the outermost shell electrons are much further away from the nucleus
Let's Think 1 40.1 Characteristic Properties of the s-Block Elements (SB p.40) Low Electronegativity • Group II elements • more electronegative than the Group I elements • the increase in effective nuclear charge • the attractive force between the nucleus and the outermost shell electrons becomes stronger
4Li(s) + O2(g) 2Li2O(s) lithium oxide 40.1 Characteristic Properties of the s-Block Elements (SB p.41) 1. Group I Elements • Lithium • when it is burnt in air, it forms normal oxide only
4Na(s) + O2(g) 2Na2O(s) sodium oxide 4Na2O(s) + O2(g) 2Na2O2(s) sodium peroxide 40.1 Characteristic Properties of the s-Block Elements (SB p.41) 1. Group I Elements • Sodium • when it is burnt in an abundant supply of oxygen • forms both the normal oxide and the peroxide
