C7 - Covalent Bonding

Front 1

Describe the formation of single covalent bonds in H₂, Cl₂, H₂O,CH₄, NH₃ and HCl as the sharing of pairs of electronsleading to the noble gas configuration

Back 1

dIn the formation of ions when a metal and non-metal react together, the electrons are transferred from the outer shell of the metal to the outer shell of the non-metal. When two non-metal atoms react they share a pair of electrons. This is called covalent bonding. In a hydrogen molecule, both hydrogen atoms share one electron with each other to form a pair. This pair of shared electrons is a single covalent bond.

Front 2

Deduce the formula of a simple compound from the relative numbers of atoms present

Back 2

We can work out the formula of a compound by knowing the valencies of the elements it contains. The valency of an element corresponds to its group (Group I - 1 valency, Group II - 2 valencies etc.). A simple way of deducing the formula is by switching each element's respective valency.

Front 3

Deduce the formula of a simple compound from a model or a diagrammatic representation

Back 3

If we are given a picture of a molecule showing all atoms and bonds, we can easily work out its formula. We do this simply by counting the number and type of each atom.

Front 4

Describe the electron arrangement in more complex covalent molecules such as N₂, C₂H₄,CH₃OH and CO₂

Back 4

Many molecules contain three or more different atoms. If we have three types of atoms, we simply add another different symbol for the third. Compounds with double or triple bonds need twice or thrice the number of electrons from each atom affected.

Front 5

Describe the differences in volatility, solubility, electrical conductivity and melting / boiling points betweenionic and covalent compounds

Back 5

Ionic compounds have high melting and boiling points because of the strong attractive forces between the ions. They are soluble in water but insoluble in organic solvents. Ionic compounds conduct electricity only when molten or when dissolved in water. This is because the ions are mobile.

Covalent compounds have low melting and boiling points because the intermolecular attractive forces are weak. There are some exceptions - giant covalent structures such as diamonds have very high melting points. They are insoluble in water, with some exceptions - sugar and some amino acids. They do not conduct electricty because they have no ions, only uncharged molecules.

Front 6

Describe the giant covalent structures of graphite and diamond

Back 6

In some covalent structures, there is a network of covalent bonds throughout the whole structure. We call these structures giant covalent structures. Diamond and graphite are both giant covalent structures.

Front 7

Relate the giant covalent structure to its uses

Back 7

Diamond has very high melting and boiling points, and as well as that, diamond is very hard. That is why diamond is used for cutting and drilling metals and glass. Diamond forms colourless glittering crystals and is therefore also used for jewellery.

Graphite has high melting and boiling points. However, the bonding between the layers in graphite is weak. This means that the layers can slide over each other if a force is applied and is why graphite is used as a lubricant. Graphite also has delocalised electrons and can be used as a conductor.

Front 8

Describe the macromolecular structure of silicon(IV) oxide (silicon dioxide)

Back 8

In silicon(IV) oxide, each silicon atom is bonded to four oxygen atoms but each oxygen atom is bonded to only two silicon atoms. This accounts for the formula SiO₂

Front 9

Describe the similarity in properties between diamond and silicon(IV) oxide, related totheir structures

Back 9

Silicon(IV) oxide has a similar structure to diamond. They also have similar properties. Silicon(IV) oxide forms very hard colourless crystals and has high melting and boiling points. It also cannot conduct electricity.