covalent bonding UPDATED

covalent bond

a strong electrostatic attraction between the negatively charged shared electrons and the positive nuclei

how do you know what bonds with what in order to make dot and cross diagrams

- look at the charge on each ion

- this tells you about how many bonds it can form (each shared electron is a covalent bond)

- then you can work it out from there)

in ammonia (NH3) what bonds to what

each hydrogen bonds to the nitrogen

in water what bonds to what

each hydrogen bonds to the oxygen

in carbon dioxide what bonds to what

each oxygen bonds to the carbon

in methane what bonds to what

each hydrogen bonds to the carbon

in ethane what bonds to what

all hydrogens bond to a carbon and carbons bond to each other

in chloromethane what bonds to what

all hydrogens bond to carbon and chlorine bonds to carbon

in ethene what bonds to what

carbons bond to each other and all hydrogens bond to a carbon

what structures are there for covalent bonding

- simple molecular structures

- giant covalent structures

why do simple molecular structures have low bpt and mpt

- atoms within molecule held together by very strong covalent bonds

- however intermolecular forces between molecules are very weak

- little energy needed to overcome weak intermolecular forces

- therefore low bpt and mpt

why do the mpt and bpt of substances with simple molecular structures increase as relative molecular mass (Mr) increases

- intermolecular forces are stronger between molecules with higher Mr

- this is bc there are more points along larger molecules for intermolecular forces to act

- so more energy needed to break the forces

- mpt and bpt increase

what physical state are most simple molecular substances

usually gases, liquids or easily melted solids at room temp

which do giant covalent structure have very high bpt and mpts

- all the atoms are bonded to each other by strong covalent bonds

- there are lots of these bonds

- this means lots of energy is needed to break them

- therefore very high mpt and bpts

can giant covalent structures conduct electricity

no charged particles so generally cannot conduct electricity

are giant covalent structures soluble or insoluble in water

usually insoluble in water

can simple molecular structures conduct electricity

- no overall charge or charged particles

- cannot conduct electricity

2 examples of giant covalent structures

- diamond

- graphite

why does diamond have a high mpt/bpt

- made up of carbon atoms that each form 4 covalent bonds

- these covalent bonds are strong and take lots of energy to overcome

- high mpt/bpt

why is diamond hard

- strong covalent bonds hold the atoms in a very rigid lattice structure

- so it is really hard

electrical conductivity of diamond

- does not conduct electricity

- no charged particles that are free to move

examples of charged particles

electrons or ions

why is graphite soft and slippery

- each carbon atom only forms 3 covalent bonds

- this creates layers of carbon atoms

- the layers are only held together weak forces

- this means they can slide over each other

- this makes graphite soft and slippery

why does graphite have a high bpt/mpt

- the covalent bonds in the layers are strong

- they require lots of energy to break

why can graphite conduct electricity

- carbon only makes 3 bonds instead of 4

- this means that only 3 of carbons outer electrons are used in bonds

- so each carbon atom has one delocalised electron

- this is charged and is free to move

example of simple molecular structure

C60 fullerene

what are C60 fullerene molecules

hollow spheres made up of 60 carbon atoms

why is C60 fullerene soft

- molecules only held together by weak intermolecular forces

- so they can slide over each other

- this means the material is soft

why is C60 fullerene a poor electrical conductor

- it does have charged particles (each carbon forms only 3 bonds, so each carbon has 1 delocalised electron)

- but the electrons can't move between molecules

- so C60 fullerene is a poor electrical conductor

what is the name for C60 fullerene

buckminsterfullerene

what is the bpt/mpt of C60 fullerene like and why

- low mpt/bpt

- bc weak intermolecular forces between the C60 molecules

- and little energy needed to overcome these

what does diamond look like

what does graphite look like

what does C60 fullerene look like

do covalent compounds usually conduct electricity

no