Lewis theory of bonding

Question 1

octet rule

Answer 1

main-group elements tend to bond in a way that each atom has eight electrons in its valence shell

= same electronic configuration as a noble gas (stable arrangement)

Question 2

stable arrangement

Answer 2

has low energy

Question 3

changes in energy

Answer 3

gain energy (unfavourable)

lose energy (favourable)

Question 4

electron affinity

Answer 4

energy released by adding an electron to an atom to form an anion (-ve charge)

high EA on right side of periodic table

Question 5

ionisation potential

Answer 5

energy required to remove an electron to form a cation (+ve charge)

low IP on left side of periodic table

Question 6

ionic bonding

Answer 6

complete transfer of one or more electrons so that both achieve a stable octet

held together by attractive electrostatic interaction between oppositely charged ions

Question 7

covalent bonding

Answer 7

atoms combine by mutual sharing of one or more electron pairs so that both achieve a stable octet

held together by increased electron density in the region between the nuclei = more favourable interactions

Question 8

heteronuclear diatomic

Answer 8

diatomic molecule containing two different atoms

e.g. HF, CO

Question 9

bond order

Answer 9

measure of number of bonds between a pair of atoms

e.g. single = order of 1
double = order of 2

Question 10

hypervalent

Answer 10

expanded octet

Question 11

lone pairs

Answer 11

non-bonding electrons

Question 12

rules for Lewis structures

Answer 12

incomplete octets are allowed but indicate an unstable or highly reactive species

first row atoms (Li-Ne) never have > 8 valence e-

second row atoms might expand valence e- to 10/12

Question 13

dative bond

Answer 13

source of both bonding e- is one atom