GCSE Chemistry C2 - Chemical Bonds and Types of Bonding

ionic bonding

• compounds formed from metals combined with non-metals

• represented by a dot and cross diagram

• The strong electrostatic attraction between oppositely charged ions formed when metal atoms transfer electrons to non-metal atoms which then makes the metal positively charged ion and the non-metal negatively charged ion

Covalent bonding

• particles are atoms which share paires of electrons.

• strong bond

• compounds formed from non-metals

• Some covalently bonded substances have very large molecules, such as polymers.

• small molecules have strong covalent bonds within their molecules

draw dot and cross diagrams for:

• hydrogen

• ammonia

• chlorine

• oxygen

• nitrogen

• hydrogen chloride

• water

• methane

metallic bonding

• occurs in metallic elements and alloys

• sharing of delocalised electrons gives rise to strong metallic bonds

• bonding between positive ions and delocalised electrons

ionic compounds

- giant ionic lattice

- held together by strong electrostatic forces of attraction between the oppositely charged ions

- forces act in every direction as the structure is 3D

how to work out empirical formula from giant lattice

• count every molecule of each element and put it in a ratio

• simplify the ratio

what are the limitations of using stick and ball diagram to represent an ionic lattice

they don't accurately represent ion sizes

particle theory

- the amount of energy needed to change state depends on the strength of the forces between the particles of the substance

- the nature of the particles involved depends on the type of bonding and the structure of the substance

- the stronger the forces between the particles the higher the melting and boiling point of the substance

what are the limitations of the simple model of the 3 states of matter

- there are no forces

- all particles are represented as spheres

- spheres are solid and inelastic

properties of ionic compounds

- regular structures in which strong electrostatic forces of attraction in all directions between the oppositely charged ions

- high melting and boiling points because a lot of energy is needed to break the many strong bonds

- when melted of dissolved in water, they conduct electricity because the ions are free to move and carry charge. but can't when in a solid state as they are in a fixed position

properties of small molecules

- substances that consist of small molecules are usually gases or liquids that have low boiling and melting points

- they have weak intermolecular forces between the molecules. these forces increase with size of molecules. it is these intermolecular forces that are overcome, not the vocalent bonds when the substance melts or boils

- substances that consist of small molecules don't conduct electricity because small molecules do not have an overall charge

polymers

- have very large molecules

- atoms are linked to other atoms by covalent bonds

- intermolecular forces between polymer molecules are relatively strong and so these substances are solids at room temp

Giant covalent structures

• linked by strong covalent bonds

• substances in giant covalent structures are solids with very high melting points

• diamond ,graphite are examples

• bonds need to be overcome to melt or boil these substances

properties of metals

• metals have high melting and boiling points as they have strong metallic bonding in their giant structures

• layers of atoms in metals are able to slide over eachother as they are arranged in layers so metals can be bent and shaped

• pure metals are too soft for many uses and so are mixed with other metals to form alloys which are harder

metals as conductors

- good conductors of electricity bc delocalised electrons carry charge throughout the structure

- good conductor of thermal energy because energy is transferred by the delocalised electrons

diamond

- each carbon atom is joined to 4 other carbon atoms covalently in a giant covalent structure so:

- very hard, very high melting point

- does not conduct electricity

graphite

- each carbon is covalently bonded to 3 other carbons, forming layers of hexagonal rings which have no covalent bonds between the layers

- layers can slide over eachother due to no covalent bonds between the layers but weak intermolecular forces. graphite is soft and slippery

- one electron from each carbon atom is delocalised. it can conduct electricity unlike diamond because the delocalised electrons can move

graphene

- single layer of graphite

- very strong because atoms within the layers are tightly bonded and it is elastic because the planes of atoms can flex relatively easily without the atoms breaking apart

Fullerenes

- molecules of carbon atoms with hollow shapes, based on hexagonal rings of carbon atoms but may contain rings with 5 or 7 carbon atoms (bucky ball/ C60/ buckminsterfullerene)

- Hexagonal rings of carbon atoms

- used to transport drugs in the body, lubricants, and catalysts

carbon nanotubes

- cylindrical fullerenes

- useful for nanotechnology, tehcnology and reinforcing materials such as tennis rackets

- very high length to diameter ratios

Nanoparticles

- 1-100 nanometres in size

- contain a few hundred atoms

- smaller than fine particles 100 - 2500nm

- course particles are known as dust (1× 10^-5 to 2.5 × 10^-6 m)

- as the size of cube decreases by a factor of 10, the surface area to volume ratio increases by a factor of 10

- a nanoparticle has different properties to the bulk chemical its made from, because of the high surface area to volume ratio. it means that smaller quantities are needed to be effective than for materials with normal particle sizes such as fullerenes have different properties to big lumps of carbon

uses of nanoparticles

- high surface area to volume ratio so they make a good catalyst

- produce highly selective sensors

- make stronger, lighter building materials

- sun tan cream, deodorant. they make no white mark

- lubricant coatings as they reduce friction. used for gears or artificial joints

- conduct electricity so can be used in small electrical circuts for computers

disadvantages of nanoparticles

- toxic to people

- may be able to enter the brain from the bloodstream and cause harm