chemistry- bonding, structure & energy

ionic bonding

strong electrostatic attraction between oppositely charged ions

ionic bonding forms between

metals and non-metals

how does ionic bonding work?

electrons are transferred from the metal to the non-metal, leaving the metal as a positively charged cation, and the non-metal having gained electrons as a negatively charged anion. These opposite charges form the strong attraction known as the ionic bond.

what is the structure of ionic bonding?

a 3D lattice of oppositely charged cations and anions- because the bond attraction acts in all directions at once causing all oppositely charged neighbours to stack together.

covalent bonding

shared pair of electrons between two atoms

covalent bonding forms between

two non-metals

how does covalent bonding work?

neither atoms can give electrons away easily as non-metals, so instead they share electrons and both count them towards a full octet. Both positive nuclei are attracted to the same negative pair, and this shared attraction is what holds the atoms together- the covalent bond.

molecular

weak attractions between separate molecules known as ‘intermolecular forces’ and are the forces overcome when heated, not the covalent bonds inside the molecule.

Metallic bonding

the attraction between a lattice of positive metal ions and a sea of delocalised electrons

metallic bonding forms between

metals only

how does metallic bonding work?

each metal atom holds its few valence electrons loosely and release them into a shared pool and these released electrons become delocalised (they belong to no particular atom and are free to move through whole structure) and the fixed metal atoms become cations (positively charged as they have lost electrons). The metal cations and delocalised electrons are attracted to each other non directionally and this holds the lattice together.

covalent network

atoms joined by covalent bonds extending through an entire 3D lattice

difference between molecular and covalent network

both have covalent bonds, but one is small molecules while the other is a giant lattice

shape and arrangement paragraph structure

… has … regions of negative charge around the central … atom. These regions maximise separation to minimise repulsion, giving a … arrangement with a … bond angle. … of these regions are bonded, and … are lone pairs, giving the molecule a … shape.

arrangement name and bond angles

2- linear- 180

3- trigonal planar- 120

4- tetrahedral- 109.5

why do some atoms have same arrangement and shape name?

if every region is bonded- (tetrahedral 4,0), (trigonal planar 3,0), (linear 2,0)

why do lone pairs repel stronger than bonding pairs?

only held by one nucleus, so sits closer to central atom

steps of finding shape

1) draw lewis structure

2) count regions of negative charge and name arrangement and angle

3) count lone pairs and name shape

shape names

tetrahedral= trigonal pyramid 3,1- bent 2,2

trigonal planar= bent 2,1

what elements can only bond a specific number?

H-2, Be-4, B-6

polar meaning (asymmetrical or symmetrical)

molecule/bond that has bond dipoles and an uneven distribution of electrical charge meaning it is arranged asymmetrically

non-polar meaning (asymmetrical or symmetrical)

molecule/bond that doesn’t have dipoles and because it has no distinct positive or negative ends, is arranged symmetrically

electonegativity

how strongly an atom pulls on the shared electrons in a bond

where does electronegativity increase on a periodic table?

across and up

what do bond dipoles mean?

different atoms hold different attractions to the bonded pair of electrons, and causes an unequal sharing of these electrons as one is pulled closer to the shared pair.

steps of finding polarity

1) are there bond dipoles NO-non-polar molecule

2) is it arranged symmetrically? NO- polar molecule

3) are there the same bonds? NO- polar molecule, YES- non-polar

to be non-polar, molecules must be

equal in size, and evenly directed

symmetrical shapes

tetrahedral, trigonal planar, linear

asymmetrical shapes

trigonal pyramid, bent

polarity writing structure paragraph

… contains … (atom-atom) bonds, which create bond dipoles due to the difference in electronegativity between … and …. Because of the … shape, these bond dipoles are/not arranged symmetrically around the central atom, and therefore bond dipoles can/cannot cancel out even though they are same size, meaning overall, … is …

what makes forces stronger

larger and more polar molecules, as attractions are stronger, and stronger attractions mean higher MP and BP

what breaks in a molecular structure

the weak intermolecular forces between separate molecules are overcome, not the strong covalent bonds inside them.

giant vs. simple structures

giant- ionic, metallic, covalent network (one continuous structure of billions of particles)

simple- molecular (small separate particles)

2D covalent network

Graphite- flat layers of hexagonal rings with only weak forces between them and becomes conductor

3D covalent networks

Diamond, silicon dioxide, silicon - atoms bonded in all directions

what to look for when naming properties

1) what holds the particles together,

2) whether there are charged particles free to move

what are particle names for each structure?

ionic, metallic- ions

covalent network- atoms

molecular- molecules

melting points of each structure

molecular- low MP as weak IMF

ionic- high MP as strong lattice attraction

metallic- high MP as strong attraction with electron sea

covalent network- very high MP as strong bonds in 3D lattice

MP or BP writing key points

1) what structure is it

2) what is being overcome

3) how much energy does that take

conductivity of structures

molecular and covalent network- never conducts due to being neutral atoms with no charges and no electrons/ions, as well as covalent bonds are fixed in place

ionic- molten or dissolved as only when ions can move around and create a current

metallic- always conduct as delocalised electrons are free to move through whole structure

why can graphite conduct when it is a covalent network?

2D layers of hexagonal rings where each carbon bonds to 3 others, so 4th electron is not bonded and becomes delocalised and free to move. other covalent networks contain 4 bonds, so each valence electron is fixed.

malleability

the ability to be hammered or rolled into a sheet without breaking

ductility

whether it can be drawn into wire without snapping (substance changes shape rather than fracturing)

malleability of structures

molecular- N/A as not solid usually, soft

ionic- no, brittle as layers slide resulting in like charges next to each other which repel strongly and break lattice, hard

metallic- yes, layers of cations mover over when force is applied but delocalised electrons move with them and the attraction remains unchanged as like charges aren’t brought together and attraction is non-directional CHANGES SHAPE

covalent- no, brittle as layers of atoms are fixed and directional, fractures under stress

like dissolves like

polar and ionic solutes dissolve in polar solvents

non-polar solutes dissolve in non-polar solvents as forces between solvent are same as between solute, so nothing prevents mixing

polarity of structures

molecular- depends on polarity (polar dissolves in polar, non-polar in non-polar)

ionic- dissolves in polar solvents like water

metallic and covalent networks- doesn’t dissolve as giant structures are too strong to be pulled apart

when does a substance dissolve?

when the attractions of solute-solvent are strong enough to overcome the existing solute-solute and solvent-solvent attractions. if not, the substance remains a lattice.

why do ionic substances dissolve in water?

anions in the lattice are drawn to the positive hydrogen ends of water molecule, and cations are drawn to the negative oxygen ends of the water molecule. These strong attractions overcome the attractions within the lattice, so ions are pulled out of the lattice and move through the water and dissolve.

enthalpy

the chemical energy stored in a substance

bond enthalpy

the energy needed to break one mole of a particular bond

exothermic

energy is released to surroundings, temperature around gets hotter, products are lower than reactants, NEGATIVE

endothermic

energy is absorbed from surroundings, temperature around gets colder, products are higher than reactants, POSITIVE

change in enthaply unit

kJ mol-1

equation for energy

energy=moles x change in enthaply

equation for energy when there is more than 1 mole of a molecule

energy=moles/coefficient x change in enthalpy

equation for finding moles and unit for each

n=m/M (n=moles (mol), m=mass (g), M=molar mass (gmol-1)

finding moles from a solution equation and units

n=cV (c=concentration (mol L-1), V=volume (L))

how to find molar mass?

add the atomic mass of every atom

is changing state an enthalpy change?

yes, because breaking bonds requires energy, and making bonds releases energy

rule for changing state enthalpy

energy in to break, energy out to make

seperating particles (melting, boiling) is endothermic or exothermic?

endothermic, as energy is absorbed to seperate particles

bringing particles together (condensing, freezing) is endothermic or exothermic?

exothermic, as energy is released as atoms settle into a lower-energy arrangement

why does boiling take longer than melting?

because when boiled, particles are being completely separated and drawn far apart as individual particles and this requires more energy and time than partially separating particles when melting

bond enthalpy equation

enthalpy= bonds broken (total reactants) -bonds formed (total products)