Topic 2: covalent bonding

Question 1

describe covalent bonding

Answer 1

the electrostatic attraction between non-metals which share a pair of electrons

Question 2

define electrostatic attractions?

Answer 2

an electrostatic attraction is when two or more oppositely charged particles are attracted to each other

Question 3

name some key examples of covalent bonding

Answer 3

H2 - hydrogen
Cl2 - chlorine
NH3 - ammonia
HCl - hydrochloric acid
N2 - nitrogen

Question 4

name the 2 different types of covalent structures

Answer 4

giant covalent structures
simple molecular

Question 5

why do simple molecular substances have low boiling and melting points?

Answer 5

simple molecular substances have strong covalent bonds within the molecules, but the intermolecular forces are very weak
this makes the molecules easy to separate
however, the larger the atom the more intermolecular forces they have meaning they have a higher melting point (e.g the halogens)

Question 6

describe the structure of a giant covalent structure

Answer 6

all the atoms are bonded together by strong covalent bonds
there are lots of these bonds meaning they require large amounts of energy to break the bonds

they don’t conduct electricity - in any state (except for graphite)
insoluble in water
examples are diamond and graphite which are only made from carbon atoms.

Question 7

describe the structure of diamond

Answer 7

each carbon atom forms 4 covalent bonds
high melting and boiling point
rigid lattice structure
don’t conduct electricity

Question 8

why can’t diamond conduct electricity?

Answer 8

each carbon atom is covalently bonded to 4 other carbon atoms so each carbon atom has no freely moving delocalised electron.

Question 9

describe the structure of graphite

Answer 9

each carbon atom only covalently bonds with 3 other carbon atoms
this creates layers of graphene which make up graphite
the layers are held together by weak forces (make sure you don’t saw intermolecular forces)
it has a high melting point so lots of energy is needed to break the covalent bonds

Question 10

why is graphite used in pencils?

Answer 10

between the layers in graphite, there are week forces of attraction
this allows the layers to slide over each other easily

Question 11

how can graphite conduct electricity?

Answer 11

each carbon atom is only covalently bonded to three other carbon atoms so each carbon atom has one freely moving delocalised electron which can move between the layers

Question 12

is C₆₀ fullerene simple molecular or giant covalent?

Answer 12

simple molecular

context
Fullerenes are made of carbon atoms joined by covalent bonds, but unlike giant covalent structures (like diamond or graphite), they exist as molecules with a fixed number of atoms (e.g., C₆₀).
They have strong covalent bonds within the molecules but only weak intermolecular forces between them.
(don’t need to know this for the exam)

Question 13

describe the structure of C₆₀ fullerene

Answer 13

• they are hollow spheres made up of 60 carbon atoms
• C₆₀ fullerene has strong covalent bonds between the carbon atoms within the molecule, forming a spherical shape made of hexagons and pentagons.
• However, the forces between separate C₆₀ molecules are weak intermolecular forces.

Question 14

can C₆₀ fullerene conduct electricity?

Answer 14

like graphite, each carbon atom has one delocalised electron
however the electrons cannot move between the molecules so it is a poor conductor of electricity

Question 15

what are the uses for C₆₀ fullerene?

Answer 15

medicinal use
C₆₀ molecules can carry drugs into the body because they are hollow
some are used as catalysts
developing technology for use in nanotechnology