Topic 2 - Chemical bonding and structure

what is the structure of an ionic lattice

alternating positive and negative ions8

what is the structure of metallic structures

cations surrounded by delocalised electrons

what is the structure of simple covalent molecules

individual molecules held by intermolecular forces

what is the structure of giant covalent structures

atoms held together by covalent bonds

what properties do ionic structures have

soluble in water, conductive when molten, solid at room temp, high melting and boiling point

why are ionic structures soluble in water

the positive and negative ions can interact with the polar water molecules

why can ionic structures only conduct when molten

when solid the ions are in a fixed position however when molten the negative ions can move around and carry charge

why are ionic structures solid at room temperatures with high melting and boiling points

the strength of their bonds

why are metallic structures highly conductive

they have delocalised electrons that can move around and carry charge

why are metallic structures solid at room temp with high melting and boiling points

metallic bonds are very strong

why do simple covalent molecules have low melting and boiling points

weak intermolecular forces

which giant covalent structures are conductors

graphene and graphite

why can graphene and graphite carry charge

only bond three times per carbon atom so have delocalised electrons

why are giant covalent structures insoluble

strong covalent bonds

what is an ionic bond

the electrostatic attraction between oppositely charged ions

what are cations

positive ions that are usually metals or hydrogen

what are anions

negative ions

how does ionic radius change down a group

decreases

why does ionic radius decrease down a group

more electron shells so more shielding

how does ionic radius change across a period

decreases for cations but increases for anions

why does ionic radius decrease for cations

more protons are present increasing the electrostatic attraction

why does ionic radius increase for anions

the addition of electrons results in more shielding

what is covalent bonding

electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms

what is dative bonding also referred to as

coordinate bonding

what is bond energy

energy required to break one mole of a covalent bond in a gaseous state

what is electronegativity

measure of an atoms ability to attract the shared pair of electrons in a covalent bond towards itself

what is the pattern for electronegativity

increases across a period, decreases down a group

why do we get polar bonds

due to differences in electronegativity

what determines how polar a bond is

the size of the difference

if the difference in electronegativity is less than 1 what type of bond is it

non-polar covalent

if the electronegativity difference is between 1-2 what type of bond it is

polar covalent

if the electronegativity difference is above 2 what type of bond is it

ionic

what other name do London forces go by

dipole-induced-dipole

how strong are London forces

weak

where are London forces found

everywhere

how strong are dipole-dipole forces

moderate

where are dipole-dipole forces found

in polar molecules

how strong are hydrogen bonds

strong

where are hydrogen bonds found

in polar H-F, H-O, or H-N bonds

why do London forces form

due to temporary fluctuations in electron distribution around atoms

what will uneven distribution of electrons around an atom create

a temporary dipole

how do permanent dipole-dipole bonds form

unequal sharing of electrons in covalent bonds

what is permanent dipole-dipole bonds

electrostatic attraction between partial positive and partial negative charges

what properties do substances that form hydrogen bonds have

soluble in water, higher melting and boiling points

what makes up a polar solvent

polar molecules

what makes up a non-polar solvent

non-polar molecules

what type of solvent to ionic compounds dissolve in

polar

what do alcohols dissolve in

water as they can form hydrogen bonds

why don’t all polar molecules dissolve in water

some don’t have strong enough dipoles

what are the properties of diamond

very hard, high melting point, thermal conductor, insoluble, electrical insulator

name some properties of graphite

soft + slippery, electrical conductor, lower melting point

name some properties of graphene

good electrical and thermal conductor, very strong

what is metallic bonding

electrostatic attraction between positively charged metal ions and negatively charged delocalised electrons

what is the strength of metallic bonds determined by

number of delocalised electrons, charge of cation, radius of cation