Key concepts in chemistry- ionic and covalent bonding, types of substanc

negative ion

anion

positive ion

cation

define ionic bond

the electrostatic force of attraction beween positive and negative ions

(between a metal and a non metal)

how are ionic bonds formed?

transfer of electrons between atoms to produce cations and anions

dot and cross diagrams

number of protons in an ion

atomic number

number of electrons in an ion

The atomic number - the charge

number of neutrons in an ion

mass number - atomic number

explain the formation of ions in groups 1, 2, 6 and 7

what happens to the name of 2 substances when they become an ionic compound?

the non-metal substance's ending goes to -ide

e.g. sodium + chlorine = sodium chloride

when happens to the name of 3 or more substances when they become an ionic compound?

end of polyatomic ions change to -ate

e.g. sulfate

deduce the formulae of ionic compounds

criss-cross method

structure of ionic compound

1. lattice structure

2. consisting of a regular arrangement of ions

3. held together by strong electrostatic forces between oppositely charged ions

covalent bond definition

the electrostatic force of attraction between a shared pair of electrons and positive nuclei

what does covalent bonding form?

molecules

why are the bonds between molecules easy to overcome but covalent bonds are strong?

because the bonds between molecules are weak

but the bonds within molecules (the covalent bonds) are strong

order of magnitude of atoms and small molecules

atoms are smaller than molecules

(atoms are joined together covalently to make molecules)

dot and cross diagram for carbon dioxide

ionic compounds are made up of...

metals and non metals

ionic compounds properties

- high MPs and BPs

- Many are soluble in water

- conduct electricity when molten or in a solution

simple molecular substances are made up of...

non metals

simple molecular substances properties

- low MPs and BPs

- a few are soluble in water

- don't conduct electricity

giant covalent compounds are made up of...

non metals

giant covalent properties

- high mps and bps

- insoluble in water

- don't conduct electricity (except graphite)

metals are made up of...

metals

metallic bond definition

the electrostatic force of attraction between positive metal ions and negative delocalised electrons

metallic structure

regular lattice structure of positive metal ions in a 'sea' of delocalised electrons

metallic bonds properties

- High MPs and BPs

- Insoluble in water

- Conducts electricity

how can substances have high melting points?

if they have many strong bonds which require lots of energy to overcome

how can substances conduct electricity?

if they have charged particles that can freely move

how can a substance not conduct electricity?

if they have no charged particles, or charged particles that cannot freely move

why do ionic compounds have high MPs and BPs?

due to strong electrostatic forces of attraction between oppositely charged ions

which require a lot of energy to overcome

why can an ionic compound conduct electricity when molten/aqueous, but not when solid?

WHEN SOLID: cannot conduct because the charged particles cannot move

WHEN MOLTEN/AQUEOUS: can conduct because the charged particles are free to move

why do simple molecular structures have low MPs and BPs?

because the weak intermolecular foces between molecules require little energy to overcome

why can't simple molecular structures conduct electricity?

because there are no charged particles or delocalised electrons

allotropes of carbon (3)

1. graphene

2. graphite

3. diamond

4. buckminster fullerene (C60)

what type of substance are the allotropes of carbon?

giant covalent

structure of diamond

- each carbon is joined covalently to 4 other carbon atoms

- this means that there aren't any delocalised electrons so diamond can't conduct electricity

- hard

- very high MP

structure of graphite

- each carbon joined covalently to 3 others, forming layers of hexagonal rings, which have no covalent bonds beween layers

--> the layers can slide over each other due to weak intermolecular foces between layers

--> meaning that graphite is soft and slippery

- 1 electron from each carbon atom is delocalised, meanign that graphite can conduct electricity

what is graphite used for an why?

lubricants:

sheets of carbon atoms (graphene) are held together by weak forces of attraction.

this allows the layers to slide over each other, making graphite soft and slippery, useful as a lubricant

what is diamond used for and why?

cutting tools:

diamond is very hard because of it's tetrahedral arrangement of carbon atoms, held together by strong covalent bonds

this makes diamond useful for tools to cut things, as it will be harder than what needs to be cut.

examples of fullerenes

C⁶⁰ (bucky ball)

graphene

properties of C⁶⁰ and graphene

- both simple covalent structures

- where a carbon atom is bonded to 3 others

- buckminster fullerine has 60 carbons which form a ball

- graphene is a sheet

- fullerenes have low MPs because of weak intermolecular forces between fullerine molecules. this also makes them soft and slippery

- graphene can conduct (delocalised electrons), but bucky ball can't (even though delocalised electron, cannot transfer between molecules)

simple polymers consist of...

large molecules containing chains of carbon atoms

example of polymer with a long chain of carbon atoms

poly(ethene)

made up of ethene monomers

properties of metals

malleable

can conduct electricity

solids with high mps and bps

shiny

high density

why are metals malleable?

when a metal is hit, the layers of ions slide over each other

the 'sea' of electrons holds the ions together so the metal changes shape instead of breakign

why can metals conduct electricity?

because the delocalised electrons can move randomly in all directions, so can carry a current

properties of non-metals

low melting points

dull

brittle

low density

poor conductors of electricity

dot and cross model

shows how electrons are shared in covalent bonds

dot and cross model limitations

Doesn't show relative sizes of atoms or intermolecular forces.

ball and stick model

shows which atoms are joined together and show the shape of structure

ball and stick model limitations

show atoms too far apart

not really 'sticks holding atoms together'