Y9 Chemistry - Covalent bonding

Covalent bond –

a shared pair of electrons between two non metal atoms

Electron sharing –

each atom contributes one or more electrons to the shared pair

Reason for covalent bonding –

atoms form covalent bonds to gain a full outer shell and become more stable (like a noble gas)

Elements involved –

covalent bonds form between non metals only

Single covalent bond –

one shared pair of electrons between two non metal atoms

Single bond examples –

H₂, Cl₂, H₂O, CH₄

Double covalent bond –

two shared pairs of electrons between two atoms

Double bond example –

O₂

Triple covalent bond –

three shared pairs of electrons between two atoms

Triple bond example –

N₂

Dots and crosses –

represent electrons from different atoms

What must be shown –

correct number of outer shell electrons, shared electron pairs, and different symbols for different atoms

Simple covalent substances –

made of small molecules such as H₂, O₂, H₂O, CO₂, and CH₄

Bonding within molecules (simple covalent) –

strong covalent bonds between atoms in each molecule

Forces between molecules (simple covalent) –

weak intermolecular forces of attraction

Melting and boiling points(simple covalent) –

low for simple covalent substances

Reason for low melting points(simple covalent) – only weak intermolecular forces need to be overcome

Energy required(simple covalent) – little energy is needed because intermolecular forces are weak

Covalent bonds during melting(simple covalent) – covalent bonds do not break when a substance melts

Electrical conductivity(simple covalent) – simple covalent substances do not conduct electricity

Reason for no conductivity(simple covalent) – no free ions and no delocalised electrons to carry charge

State at room temperature(simple covalent) – many simple covalent substances are gases or liquids

Reason for state(simple covalent) – weak intermolecular forces mean little energy is needed to separate molecules

Effect of molecule size(simple covalent) – as molecules get bigger, intermolecular forces become stronger(but still weak)

Effect on melting point(simple covalent) – larger molecules have higher melting and boiling points(but still low)

Giant covalent structure – a huge network of atoms joined by covalent bonds

Structure type p(giant covalent) – one continuous lattice with no individual molecules

Melting and boiling points(giant covalent) – very high due to many strong covalent bonds

Energy needed(giant covalent) – a lot of energy is required to break the covalent bonds

Solubility(giant covalent) – giant covalent structures are usually insoluble

Carbon bonding in diamond – each carbon atom forms four covalent bonds

Arrangement(diamond) – tetrahedral 3D structure

Hardness(diamond) – diamond is very hard because strong covalent bonds exist in all directions

Melting point(diamond) – very high due to strong covalent bonds

Electrical conductivity(diamond) – diamond does not conduct electricity

Reason for no conductivity(diamond) – all outer

shell electrons are used in bonding

Uses(diamond) – cutting tools and drill bits

Carbon bonding in graphite – each carbon atom forms three covalent bonds

Structure (graphite)– flat hexagonal layers of carbon atoms

Delocalised electrons(graphite) – one electron per carbon is not used in bonding and becomes delocalised

Electrical conductivity(graphite) – graphite conducts electricity due to delocalised electrons carrying electric charge

Texture(graphite) – graphite is soft and slippery

Reason for softness(graphite) – layers can slide over each other because forces between layers are weak

Melting point(graphite) – high due to strong covalent bonds within each layer

Uses(graphite) – lubricants, pencils, electrodes

Graphene – a single layer of graphite that is one atom thick

Structure(graphene) – hexagonal lattice of carbon atoms

Electrical conductivity(graphene) – excellent due to delocalised electrons carrying electric charge

Other properties(graphene) – very strong and very light

Uses(graphene) – electronics and composite materials

Silicon dioxide structure – giant covalent lattice

Bonding(sio2) – each silicon atom bonds to four oxygen atoms and each oxygen bonds to two silicon atoms

Melting point(sio2) – very high due to many strong covalent bonds in all directions

Electrical conductivity(sio2) – does not conduct electricity

Reason for no conductivity(sio2) – no free electrons or ions

Uses(sio2) – sand and glass

Simple covalent substances – small molecules with weak intermolecular forces

Giant covalent structures – many strong covalent bonds throughout the structure

Conducting covalent substances – graphite and graphene only

Reason for conductivity – delocalised electrons that can move

Melting point explanation – always say weak intermolecular forces, not weak covalent bonds

Giant covalent explanation – mention many strong covalent bonds and high energy needed to break them

Graphite conductivity – always mention delocalised electrons that can move

Elements in covalent bonding – always state non

metals