The Representative Elements: Groups 1A Through 4A, Summaries of Chemistry

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Chapter 19

The Representative Elements:

Groups 1 A Through 4 A

19.1 Survey of the Representative

Elements

 Elements in group 1A through 8A are called representative elements because they display a wide range of physical and chemical properties.

 Representative elements display the range of possible valence electrons from one in group 1A to eight in group 8A.

 The valence electrons of representative elements are in s or p orbitals.

 Metals tend to lose their valence electrons to form cations with a configuration of the noble gas from the preceding period

 Nonmetals tend to gain electrons to form anins with a configuration of the noble gas in the same period

Atomic size and Group anomalies

1. H, Be, B, C, N, O & F have properties that distinguish them from their groups due to their relatively small sizes

2. H is nonmetal and forms covalent bonds; Li is metal and forms ionic bonds

3. All oxides of G 2A are ionic except that of Be (BeO) it is covalent also amphoteric.

4. Same is applicable for G 3A

5. G 5A: carbon forms readily C-C but Si forms readily Si-O

6. Si-Si exists but less stable the C-C

7. O=C=O exists but O=Si=O is not stable; Si-O-Si is stable. 8.Si does not form  bonds. Si 3p valence orbitals do not overlap with the O- 2p orbitals

  bonding is important for relatively small elements

of the 2nd^ period.

 N exists as N≡N due to tendency to form  bonds

 P exists as P 4 ; P large atoms are like Si do not form

strong  bonds. They prefer to achieve noble gas configuration but forming single bonds.

 O (G 6A) exists as O=O; tendency to form 

bonding

 S does not form  bonding thus it exists as

S 8.

 F has smaller electron affinity than Cl (not expected)

the small size of F in F-F with 6 lone pairs of electrons leads to much greater repulsion compared to Cl

Abundance and Preparation (P. 917): Self study

Abundance of Elements in the Human Body

19.2 Group 1A Elements

 ns^1 valence electron configuration.

 Comprise H and alkali metals

Alkali Metals

Selected Physical Properties of the Alkali Metals

Group 1: M(s) + H 2 O(l)  2M+(aq) + 2 (OH)-(aq) + H2(g)

• Li has the highest ionization potential and the highest oxidation

potential. Due to its small size and large energy of hydration, thus Li+ attracts water effectively and large energy is released when the ion is formed. Thus formation of Li+^ is favored and Li behaves as a strong

• Reducing agent.

Types of Compounds Formed by the Alkali Metals

with Oxygen

19.3 Hydrogen

Also prepared from the electrolysis of water

Hydrides

Covalent hydrides

Metallic/interstitial hydrides

Group 2A Elements

 Ns^2 metals. They are called “Alkaline Earth metals”

 Their oxides are basic

MO(s) + H 2 O M(OH) 2

 The differences in reactivity among them are

shown by their reaction with water:

M(s) + 2H 2 O M(OH) 2 + H 2 (g)

 Ca, Ba, Sr react easily with cold water

 Mg reacts with hot water

 Be does not react with water

Selected Physical Properties, Sources, and Methods of

Preparation for the Group 2A Elements