Covalent Bonding - Bonding and Structure

Edexcel IGCSE Chemistry

what is a covalent bond?

two or more non-metallic sharing a pair of electrons

are covalent bonds strong or weak?

strong

why are there strong bonds between atoms that are covalently bonded?

strong electrostatic attraction between the positive nuclei of the atoms and shared pairs of negative electrons

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

• weak intermolecular forces between the molecules. these forces are broken during melting/boiling not the covalent bonds

• little energy is needed to overcome these forces

why do the melting and boiling points of a substance increase with mass

the strength of intermolecular forces increases with increaseing molecular mass

why do giant covalent structures have high melting and boiling points?

• all of the atoms in the structure are bonded together by strong covalent bonds

• a lot of energy is needed to overcome these bonds

why does diamond have a high melting point?

• each carbon is covalently bonded to 4 other carbons

• to release one atom, 4 strong covalent bonds must be broken

• this requires a lot of heat energy

why does diamond not conduct electricity?

all the atoms are fixed in a lattice so there are no free electrons to carry charge

why is diamond hard?

any force applied to one atom is quickly dispersed by the three dimensional lattice to many other atoms

why is graphite soft?

• each carbon atoms is covalently bonded ot 3 other cabrons forming layers of hexagonal rings

• the layers of atoms are held together by weak intermolecular forces so are able to slide over each other easily

why can graphite conduct electricity?

• one electrons from each carbon atom is delocalised

• these electrons can move through the structure when a voltage is applied

why does graphite have a high melting and boiling point?

• to move any atom in the lattice many strong covalent bonds need to be broken

• this requires a lot of energy

what is graphene?

a single layer of graphite

what makes graphene useful?

useful in electronics and composites