Bonding

Why might the e⁻s not be shared equally betw 2 atoms that are different? (2)

(1) 1 atom may be bigger than other (↑atomic radius) (2) 1 atom may have greater nuclear charge (no. p⁺)

When show HB, (3)

(1) 3 dashed lines (2) 180⁰ across HB (3) show any lone pair(s)

Requirements for HB (2)

(1) H covalently bonded to NOF (highly elec-ve) (2) Lone pair on 2nd NOF

Why are HBs so much stronger?

(1) NOF atoms have lone pairs of e-s (2) H atoms are highly e- deficient → NOF is v. elec-ve → attracts e-s toward itself → H +ve charge and v. small → v. strong elec field (bc small)

3 types of IMFs

(1) Van der Waals Forces (2) Dipole-dipole forces (3) Hydrogen bonding

Effect of lone pairs on bond angle (2)

(1) lone pairs repel more than bond pairs (1) bond angle will be lower

Perfume is a mixture of fragrant compounds dissolved in a volatile solvent. When applied to the skin, the solvent evaporates, causing the skin to cool for a short time. After a while, the fragrance may be detected some distance away. Explain these observations. (4)

(1) solvent has low Bpt/weak IMFs (2) solvent needs E to evaporate (overcome IMFs) (3) E taken from skin (so cools) (4) fragrance slowly spreads (5) by diffusion

Because VdW Fs caused by changing position of e⁻ cloud (3)

(1)↑e⁻ = ↑inst. dipole (2) VdWF size α no e⁻ present (3) VdWF size α Ar/Mr

Dative covalent bond

(2 e-s can come from just one of the atoms) Shared pair of e⁻s (lone pair) on X donated to Y

Water - liquid - solid

(Liquid) HBs break and reform easily as molec move (Solid) water molecules not free to move - HBs held in fixed positions - molecule packed less closely - ↓ρ — form on top of ponds

evidence of spacing - s, l, g

- (s) not easily compressed - (l) not easily compressed - (g) easily compressed

Strength of HB

- 10% of covalent - weaker so can break/make in conditions where covalent unaffected

In terms of e- pairs, explain why the bond angles in NH₄⁺ are all 109⁰ (4)

- 4 bonding pairs of e⁻ - repel equally - as far apart as possible - tetrahedron

diamond

- C - macromolecular - 4 covalent bonds/ea C atom - giant 3D lattice of strong covalent bonds = v. hard = v. high Mpt = doesn't conduct elec (no free charged particles)

graphite

- C - strong covalent and weaker VdWFs - ea C forms 3 cov bonds (= 'trigonal planar') - leave spare delocalised e- in p orbital = conduct elec (deloc e-)(along planes of hexagons) = soft (layers can slide over each other (held by weak VdWF) = v. high Mpt (cov bonds)

Dipole-dipole Fs - HCl

- Cl more electronegative than H - e⁻ pulled towards Cl atom - → dipole

Explain, in terms of the IMFs present in each compound, why HF has a higher Bpt than HCl (3)

- HF = Hydrogen bonding - HCl = permanent dipole-dipole bonding - HBs strongest IMF

turning a (s) to (l) - fusion

- T doesn't change - heat E provided is absorbed as the forces betw particles are weakened

How do VdW Fs work? (5)

- at any instant, the e- cloud may be distorted - 1 side (fewer e-) = δ⁺ (& converse) - instantaneous dipole - this dipole induces polarity on another atom

2 biological examples of dative covalent bonding

- chlorophyll - haemoglobin

spacing - s, l, g

- close - close - far apart

evidence of 3 states of matter arrangement - (s)

- crystal shapes have straight edges - solids have definite shapes

evidence of movement - s, l, g

- diffusion: v. slow - expand on heating - diffusion: slow - evaporate - diffusion: rapid - exert pressure

Why is ice being less dense important?

- forms on top of ponds - insulate pond - fish live through winter - help life continue

4 basic crystal types

- ionic - metallic - molecular - macromolecular

Why do lone pairs affect bond angle? (2)

- lone pairs repel more than bonding pairs

Why are lone pairs of e- opposite each other?

- lone pairs repel more than bonding pairs - so are as far apart as possible

elec conductivity - metals - alloys - ionic - covalent

- metals & alloys: (s) and (l) -- deloc e- that hold metal ions together - (l) or (dissolved in water) -- ions - gen. don't -- no charged particles

Noble gases - BPts (4)

- molar mass increases down the group - so no. e⁻ ↑ - VdW Fs get stronger - → Bpt ↑

molecular crystals - low Mpt/enthalpies of melting

- molec held in a reg array by IMF (not covalent (w/in)) - VdWFs much weaker than covalent/ionic/metallic

macromolecular - high Mpt

- must break strong covalent bonds (- not weak IMF) e.g. graphite, diamond, SiO2

evidence of 3 states of matter arrangement - (l)

- none direct but a (l) changes shape to fill bottom of container

what happens when heat gas?

- particles gain more KE - move faster - get much further apart - expand a lot

Uses for HB (3)

- proteins (C=O, N-H) - ironing (heat breaks HBs in creased mat) - DNA (HB hold 2 strands together - templates for dna replication)

arrangement of particles - s - l - g

- regular - random - random

What does δ⁺ mean?

- slight positive charge - e- deficient

what happens when heat solid?

- supply E to particles - makes them vibrate more about a fixed posn - slightly increase avg d betw particles - solid expands

movement - s, l, g

- vibrate about a point - rapid 'jostling' - rapid

How to draw molecules with lone pairs

1. Draw dot and cross diagram (+/- e- to main middle atom for charge as needed)2. Count no. bonding and lone pairs of e- 3. See basic shape 4. Reduce angle per lone pair (2 or 2.5⁰)

dative covalent bond Qs - 2 NBs

1. must be specific with what element donates (& receives) 2. be specific with whether atom/molecule/ion (chlorine or chloride)

Dimer

2 molecules joined together

covalent bond between

2 non metals

Reduce angle how many degrees per lone pair?

2 or 2.5⁰

A bond might be covalent with a _____ of ionic character A bond might be ionic with a _____ of covalent character

A bond might be covalent with degree of ionic character A bond might be ionic with degree of covalent character

When partial charges are separated like C-Cl... what forms?

A dipole forms

What is electronegativity?

Ability of an atom to attract e⁻s/e⁻ density in a covalent bond to itself

silver ion

Ag⁺

There are weak electrostatic attractions between all atoms and molecules (VdWFs) because

All atoms made up of +ve and -ve charges (even though neutral overall)

Van der Waals forces act between

All atoms/molecules at all times

Aluminium chloride has Mr = 267 - formula?

Al₂Cl₆

what is a lone pair of e-?

An unshared electron pair in a covalent bond

VdW Fs are additional to

Any other IMFs

HB - why does NOF need lone pair of e-

Attached to δ⁺ H in another molecule → HB

2 molecules which both have dipoles will... - why?

Attract one another - no matter start position (repel → 'flip' → attract)

barium ion

Ba²⁺

Bpts - H₂O, HF, NH₃ - higher than those of the hydrides of the other elements in their group

Bc HBs betw - ↑IMF of attraction - req more E to separate

Boiling points of noble gases - gradual increase in Bpt

Bc only IMF = VdW - ↑w/ no. e- present

Shape - e⁻ pairs 2 bonding pairs 2 lone pairs

Bent 104.5⁰

Shape - e⁻ pairs 2 bonding pairs 1 lone pair

Bent 118⁰

carbonate ion

CO₃²⁻

VdW Fs caused by (1)

Changing position of e⁻ cloud

Electronegativity C-Cl bond

Cl more electronegative than C → gains partial -ve charge →→ δ⁻ C gains partial +ve charge →δ⁺

Dative covalent bond aka

Coordinate bond

Allotropes

Different forms of the same element

Dipole moment sums up

Effect of all the bonds in the molecule - in molec w/ >1 polar bond, the effects of each bond may (1) cancel → molec with no dipole moment (2) add up → reinforce each other

AlCl₃ to Al₂Cl₆

Exists as a dimer - when sublime to (g)

iron (II) ion

Fe²⁺

iron (III) ion

Fe³⁺

Element with highest electronegativity value

Fluorine

How to work out shape of molecule? e.g. SO₄²⁻

Gives shape but not double bonds

What molecules have all 3 IMFs?

H covalently bonded NOF

where do hydroxonium ions come from? e.g. HCl

HCl → H⁺(aq) + Cl⁻(aq) H⁺ ion quickly bonds to H₂O → H₃O⁺

Why does water have higher Bpt than NH₃ & HF

H₂O can form 4 HBs NH₃ - 2

HCs: Bpts

Increase as chain length increase - molar mass increases down the group - so no. e⁻ ↑ - VdW Fs get stronger - → Bpt ↑

Elements become more/less electronegative as you go down a group

Less electronegative

Electronegativity Polar bonding

Lies between the 2 extremes of ionic and covalent bonding electronegativity diff = 0.5-2.0 A bond might be only slightly polar

Shape - e⁻ pairs 2

Linear 180⁰

What scale is often used to show relative electronegativity values?

Linus Pauling's scale

What is a polar molecule?

Molecule with both a slight +ve bole and a -ve pole

Dipole-dipole Fs act between

Molecules with permanent dipoles

Elements become more/less electronegative as you go from L to R across a period

More electronegative

property that best shows giant or simple molecular

Mpt (/Bpt)

ammonium ion

NH₄⁺

sodium hydrogen sulphate

NaHSO₄

What difference does a charge have on the shape of a molecule?

None - but when drawing e-, pay attention

How does atomic radius affect electronegativity?

Nucl of smaller atom closer to shared pair of e⁻s → greater FoA betw smaller-atom nucleus & shared e⁻ pair

O-H - polar

O is more electronegative than H → pulls the shared pair of e⁻s towards itself

Shape - e⁻ pairs 6

Octahedral 90⁰

VdW Original [atom] has ___ ___ in the _____ which will be _____

Original [atom] has induced dipoles in the nearby atoms which will be attracted to original [atom]

What does pulling a shared pair of e⁻s towards itself cause? (O-H)

Partial -ve (δ⁻) charge on O atom Partial +ve (δ⁺) charge on H atom

Lead ion

Pb²⁺

How does nuclear charge affect electronegativity?

RH atom has greater nuclear charge than LH atom → greater FoA betw nucl of RH (7+) atom & shared pair of e⁻s (than LH (5+) atom and shared pair of e⁻s)

Forming bond - exo/endo

Release E - Endo

Shape - e⁻ pairs 4 bonding pairs 1 lone pair

See saw 90⁰, 120⁰

Dipole moment depends on

Shape of molecule

Covalent bond is

Share e-s - attraction between +ve nuclei and their shared e- forms bond

Shape - e⁻ pairs 4 bonding pairs 2 lone pairs

Square planar 90⁰

Shape - e⁻ pairs 5 bonding pairs 1 lone pair

Square pyramid (umbrella) 90⁰

HB - why does H atom need to be bonded to a v. elec-ve atom?

Strong partial +ve charge (δ⁺) on H atom

Shape - e⁻ pairs 4

Tetrahedral 109.5⁰

Covalent bond between 2 atoms that are the same e.g. H₂ - e⁻s?

The e⁻s are shared equally betw the atoms - identical FoA betw nucleus of ea atom & shared pair of e⁻s

Covalent bond between 2 atoms that are different - e⁻s?

The e⁻s may not be shared equally betw the atoms

What is attracted to what - H₂O molecules

The lone pair of e- on [O] of another [H₂O] molecule is strongly attracted to e- deficient H atom

Electronegativity Ionic bonding occurs when

There are big differences in electronegativity - usually betw metal and non-metal

Electronegativity Covalent bonding occurs when

There are small differences in electronegativity, - usually between 2 non-metals

Effect of double bonds on molecule shape

Treat as single bonds - behave exactly as single for repulsion purposes - shape same

Shape - e⁻ pairs 5

Trigonal bipyramid 90⁰, 120⁰

Shape - e⁻ pairs 3

Trigonal planar 120⁰

Shape - e⁻ pairs 3 bonding pairs 2 lone pairs

Trigonal planar 120⁰

Shape - e⁻ pairs 3 bonding pairs 1 lone pair

Trigonal pyramidal 107⁰

Strength of imfs - order

VdW < Dipole-dipole < HBs

electron deficient

atoms that can have less than an octet - Be, B, Al can form covalent molecules don't achieve a full outer shell

-ate on anion means e.g. sulphate

cont. O → SO₄²⁻

ionic - how to identify compound formula

crossover rule

Why is HB (N-H-O) linear (180⁰)?

e- pair in N-H covalent bond repels e-s in HB between N and H

where does the extra e come from in a hydroxide ion?

e.g. KOH → K⁺ + OH⁻ - e from K → K⁺ donated to OH → OH⁻

hypervalent elements

e.g. S, P, Si, Cl

property that best shows bonding type

electrical conductivity

E needed to melt aka

enthalpy change of melting/fusion

E needed to vaporise liquid aka

enthalpy change of vaporisation

enthalpy vs T

heat energy change measured under constant pressure T depends on avg KE of particles and so related to speed - greater E = faster

Strongest IMF

hydrogen bonding (weaker than covalent)

metallic crystals/bonding

lattice of positive ions embedded in a delocalised sea of e- - attraction of +ve to -ve (! count no. e- drawn to ion)

ionic bonding involves (3)

many strong electrostatic attraction between oppositely-charged ions in a giant ionic lattice

ionic bond is between

metal and non-metal

why do molecular crystals not conduct electricity?

no charged particles to carry charge

evidence of 3 states of matter arrangement - (g)

none direct but a gas will fill its container

-ide on anion means e.g. sulphide

only one element → S⁻

What is an intermolecular force?

the force of attraction between atoms/molecules

The greater the difference between the electronegativity values...

the greater the polarity of the covalent bond

since bond forming is exothermic, electron-deficient compounds (Be, B, Al) are still...

thermodynamically stable - E is released when the elements bond to form a molecule

ionic - electricity

will conduct if molten/dissolved