Covalent bond

Question 1

how do atoms of non-metals achieve duplet/ octet structure

Answer 1

Atoms of non-metals achieve duplet/ octet structure by sharing electrons with each other

Question 2

why don’t non-metal atoms want to lose its valence electron

Answer 2

Both non-metals have relatively large ionization energy and neither non-metal atom wants to lose its valence electron(s)

Question 3

what is covalent bond

Answer 3

It is the electrostatic force of attraction between the shared pair(s) of electrons and the positive nuclei of the two
bonding atoms.

Question 4

how do most of the non-metal elements exist as

Answer 4

they exist as diatomic molecules (except noble gases)

Question 5

Relationship between group number and number of
covalent bonds formed (4)

Answer 5

valence: 4
bonding pairs: 4
lone pairs: 0

Question 6

Relationship between group number and number of
covalent bonds formed (5)

Answer 6

valence: 5
bonding pairs: 3
lone pairs: 1

Question 7

Relationship between group number and number of
covalent bonds formed (6)

Answer 7

valence: 6
bonding pairs: 2
lone pairs: 2

Question 8

Relationship between group number and number of
covalent bonds formed (7)

Answer 8

valence: 7
bonding pairs: 1
lone pairs: 3

Question 9

covalent bond of halogens, group VII, 17

Answer 9

Hydrogen and Group VII/ 17 elements form single covalent bonds by each atom sharing one pair of electrons :

Question 10

covalent bond of group VI, 16

Answer 10

Group VI/ 16 elements form double bonds by sharing 2 pairs of electrons

Question 11

covalent bond of group V, 15

Answer 11

Group V/ 15 elements form triple bonds by sharing 3 pairs of electrons

Question 12

what is bond length

Answer 12

it is the distance between the nuclei of the two bonding atoms joined by covalent bond

Question 13

what is bond strength

Answer 13

it is the strength of electrostatic force between the shared pair of electrons and the nuclei of the two bonding atoms.

Question 14

how can bond strength be measured

Answer 14

Bond strength can be measured in terms of bond energy (unit : kJ mol-1).

Question 15

what is bond energy

Answer 15

It is the energy required to break one mole of covalent bonds from gaseous molecules.

Question 16

Relationship between bond length and bond strength

Answer 16

● As the atomic radius increases, the bond length
increases.
● The shared pair of electrons in the covalent bond
are further away from the nuclei of the two
bonding atoms.
● Weaker electrostatic force of attraction →
weaker covalent bond → lower bond energy.

Question 17

Relationship between number of bonds and bond strength

Answer 17

● As the number of shared pair electrons in the covalent bond increases, the
electrostatic force of attraction from the nuclei increases.
● The atoms are held closer and so the covalent bond is shorter and stronger.
● Bond strength: triple bond > double bond > single bond

Question 18

incomplete octet example

Answer 18

● Some atoms, like Be(Beryllium) and B(Boron),
form stable compounds with
incomplete octets.
● They prefer to form covalent bond
rather than ionic bond because of
their comparatively high ionization
energies.

Question 19

how is octet structure formed in atoms like Be and B

Answer 19

To achieve octet structure in atoms like Be and B, they form dative covalent bond

Question 20

what is dative covalent bond

Answer 20

it is a covalent bond which both electrons in the shared pair are contributed by the same atom

Question 21

dative covalent bond examples

Answer 21

Dative covalent bond is also formed when species with lone pair electrons, such as ammonia and water, react with hydrogen ions (H+), it is also found in carbon monoxide

Question 22

what is the arrow used to represent in dative covalent bonds

Answer 22

An arrow is usually used to
represent the presence of a
dative covalent bond.

Question 23

how to draw lewis structure

Answer 23

Step 1 : Identify the total number of valence electrons.

Step 2 : Identify both central atom and surrounding atoms of the species and arrange the “skeleton”
of the species.

Step 3 : Put the valence electrons to the “skeleton” of the species as bonding electrons in such a
way that the surrounding atoms can form the expected number of covalent bonds.

Step 4 : Put the remaining valence electrons to the surrounding atoms as their lone pair(s) of
electrons in such a way that they can achieve octet structure of electrons.
If some still remain, put to the central atom as its lone pair(s).

Question 24

naming and formulae of covalent compounds

Answer 24

● Limited to the binary covalent compounds - formed between
two different non-metals.

1. The first element written in the formula should be named first
   using its full name.
2. The second element in the formula should be named after the
   first one with the suffix of “ide”.
3. Prefix(es) should be included to indicate the number of each
   atom present in the molecule.
4. If the number of atom of the first element is one, then no prefix
   is needed.

Question 25

number of atoms 1-10

Answer 25

mono
di
tri
tetra
penta
hexa
hepta
octa
nona
deca

Question 26

what are acids

Answer 26

A group of covalent compounds that dissociate to give H+ ions when dissolved in water

Question 27

the two types of acid and examples

Answer 27

1. Hydro-acids: acids that do not contain oxygen
   Example - hydrochloric acid, HCl (aq)
2. Oxo-acids: acids containing oxygen
   Example - nitric acid, HNO3 (aq)

Question 28

what are hydro-acids

Answer 28

Generally contain hydrogen atoms and non-metal atoms (except oxygen).

When the acid dissolves in water, they can react with water molecules to
give a hydronium ion, H3O+
(aq) and an anion (more will be discussed in Topic 6 Acids and bases)

Question 29

naming of hydro-acids

Answer 29

The name of this group of acids consists of two parts:
● The first part is named with a prefix “hydro”, which is followed by the name of the non-metal with a suffix of “ic”.
● The second part is named with the word “acid”.

Question 30

what are oxo-acids

Answer 30

● Contain hydrogen atoms, oxygen atoms and non-metal atoms.

● When the acid dissolves in water, they react with water molecules to give a
hydronium ion, H3O+
(aq) and a polyatomic oxoanion.

Question 31

naming of oxo-acids

Answer 31

● The first part of their names: a prefix with “part of the name of the non-metal”
and a suffix of “ic” for the one with more oxygen and “ous” for the one with
fewer oxygen.

● The second part is named with the word “acid”.