Topic 2 - Bonding & Structure

Question 1

What is ionic bonding?

Answer 1

The strong electrostatic attraction between oppositely charged ions.

Question 2

What effects does the ionic radius have of the strength of ionic bonding?

Answer 2

As ionic radius increases, charge density decreases ∴ weaker bonds are made. (enthalpy = less exo)

Question 3

What effects does the ionic charge have on the strength of ionic bonding?

Answer 3

The bigger the charge difference the stronger the bond will be.

Question 4

What are the trends in ionic radii down a group for a set of isoelectronic ions?

Answer 4

(+ve) ions are smaller than their atoms as they have less electrons and a greater ration of protons to remaining electrons. (-ve) ions are larger as there are more elctrons fro the same amount of protons, so the pull is less.

Question 5

How does the migration of ions explain the existence of ions?

Answer 5

The (-ve) ions move towards the (+ve) electrode and the (+ve) ions move towards the (-ve) electrode.

Question 6

How do the physical properties of ionic compounds explain the existence of ions?

Answer 6

• high mp (strong attractive forces between ions)
• non conductor as solid (ions held together tightly)
• conductor when molten/in aq (ions free to move)
• brittle

Question 7

What is a covalent bond?

Answer 7

The strong electrostatic attraction between 2 nuclei & the shared pair of electrons between them.

Question 8

What are diative covalent bonds?

Answer 8

When the shared pair of electrons in the covalent bond come from only 1 bonding ato. (co-ordinate bonding, shown by an arrow from sharing atom)

Question 9

What is the relationship between bond lengths & strengths in covalent bonding?

Answer 9

If their is a greater force of attraction (x2/x3 bonds) the bond will be shorter but stronger.

Question 10

How do lone pairs and bonding pairs arrange themselves around a central atom & determine the molecules shape?

Answer 10

Lone pairs repel more than bonding pairs, which reduces bond angles.

Question 11

What is a linear molecule?

Answer 11

• 2 bonding pairs, no lone pairs
• 180° bond angle
• CO₂, BeF₂

Question 12

What is a trigonal planar molecule?

Answer 12

• 3 bonding pairs, no lone pairs
• 120° bond angle
• SO₃, NO₃⁻, CO₃²⁻

Question 13

What is a tetrahedral molecule?

Answer 13

• 4 bond pairs, no lone pairs
• 109.5° bond angle
• SiCl₄, SO₄²⁻, NH₄⁺

Question 14

What is a trigonal pyramidal molecule?

Answer 14

• 3 bond pairs, 1 lone pair
• 107° bond angle
• PF₃,H₃O⁺

Question 15

What is a bent/v-shaped molecule?

Answer 15

• 2 bond pairs, 2 lone pairs
• 104.5° bond angle
• H₂S, SCl₂

Question 16

What is a trigonal bipyramidal molecule?

Answer 16

• 5 bond pairs, no lone pairs
• 120° & 90° bond angles
• PCl₅

Question 17

What is an octahedral molecule?

Answer 17

• 6 bond pairs, no lone pairs
• 90° bond angle
• SF⁶

Question 18

What is a square planar molecule?

Answer 18

• 4 bond pairs, 2 lone pairs (variation or octahedral)
• 90° bond angle w/ lone above & below
• XeF₄

Question 19

What is the electron-pair repulsion theory?

Answer 19

VSEPR, used to predict the shapes of molecules as they are arranged to produce the minimum amount of repulsion/maximum separation.

Question 20

What is electronegativity?

Answer 20

The ability of an atom to attract the bonding electrons in a covalent bond to itself.

Question 21

What are the factors affecting electronegativity?

Answer 21

• ↑ across a period as protons ↑ ∴ radius ↓

- ↓ down a period as distance & shielding ↑

Question 22

How does electronegativity affect bonding?

Answer 22

• ↓ elec.neg. difference = covalent

- ↑ elec.eg. difference = ionic (>1.7)

Question 23

What is a polar covalent bond?

Answer 23

Not purely ionic or covalent. The least elec.neg. element = δ⁺ & the most elec.neg. = δ⁻

Question 24

How do you know if a bond is polar or non-polar?

Answer 24

• if symmetrical (all bonds same & no lone pairs) = non-polar even if individual bonds are (cancel out)
• CO₂ = non, CH₃Cl = polar

Question 25

What are London forces?

Answer 25

Instantaneous, induced dipole-dipole interactions, occur when fluctuations in e⁻ density causes temporary dipoles to form, which then = induced dipoles.

Question 26

What affects the strength of London forces?

Answer 26

↑ electrons = ↑ chance of temporary dipoles = stronger L forces which need ↑ energy to overcome. Seen in ↑ bp down group 7. (I₂ = solid & Cl₂ = g)

Question 27

How does the chain length of alkanes affect the size of L-forces?

Answer 27

↑ chain length = ↑ surface area of contact ∴ stronger L-forces. Branches in c-chain = ↓ points of contacts ∴ ↓ bps.

Question 28

What are permanent dipole-dipole forces?

Answer 28

- occur between polar molecules, stronger than L-forces - bond has a significant difference in elec.neg. - can occur in addition to L forces. (δ⁻ Cl in H-Cl attracted to δ⁺ H in another H-Cl)

Question 29

What are hydrogen bonds?

Answer 29

Bonds that occur in compounds that have a H atom attached to F, N or O, and an available lone pair. -occurs in addition to L-forces

Question 30

What is the reason for the shape of H-bonds?

Answer 30

They form a 180° angle around the H atom as the H gives 2 electrons which repel to min repulsion/max separation.

Question 31

How are H-bonds formed in H₂O?

Answer 31

Water forms 2 H-bonds per molecule as δ⁻ oxygen has 2 lone pairs ∴ = stronger H-bonds & ↑ pb.

Question 32

Why does ice have a lower density than water?

Answer 32

The H-bonds create interlocking rings of 6 water molecule when water freezes, creating distance between the molecules which decreases its density.

Question 33

Why do H₂O, NH₃ & HF have abnormally high bps?

Answer 33

They form H-bonds as well as L-forces which needs ↑ energy to break.

Question 34

Why do alcohols have lower volatility compared to alkanes?

Answer 34

They can form H-bonds ∴ have ↑ bps so need ↑ energy to overcome.

Question 35

What are the trends in bp of the hydrogen halides from HF to HI?

Answer 35

- HF = ↑due to H-bonds | - ↑ from HCl to HI as L-forces ↑ due to ↑ electrons

Question 36

What does 'like dissolves like' mean?

Answer 36

Compounds with similar intermolecular forces to those in the solvent will generally dissolve. (Iodine = only L-forces dissolves hexane = only L-forces.)

Question 37

Why is propane a useful solvent?

Answer 37

It has polar & non-polar characteristics, so can dissolve polar and non-polar substances.

Question 38

How is water used to dissolve some ionic compounds?

Answer 38

Water can hydrate the ions, the δ⁺ H bonds to the (-ve) ion in the bond & the δ⁻ O bonds to the (+ve) ion.

Question 39

How is hydration affected by charge density?

Answer 39

↑ charge density = ↑ hydration enthalpy, as ions attract water molecules more strongly.

Question 40

How does water dissolve simple alcohols?

Answer 40

↓ alcohols = soluble in water as can form H-bonds, as hydrocarbon chain ↑ the less soluble it becomes.

Question 41

When is water not useful as a solvent?

Answer 41

If substances cant form H-bonds (halogenoalkanes) or are non-polar (hexane) they are insoluble in water.

Question 42

What is metallic bonding?

Answer 42

The strong electrostatic attraction between metal ions & delocalised electrons.

Question 43

What are the main factors that affect the strength metallic bonding?

Answer 43

- no. of protons (↑ protons = stronger bond) - no. of delocalised electrons per atom (↑ = stronger) - size of ion (↓ ion = stronger bond)

Question 44

What are giant lattices present in?

Answer 44

- ionic solids (giant ionic lattices) - covalently bonded solids (giant covalent lattices) - solid metals (giant metallic lattices)

Question 45

What is the structure of covalently bonded substances like I₂ & H₂0?

Answer 45

simple molecular

Question 46

What are the allotropes of carbon?

Answer 46

- diamond, tetrahedral, 4 bonds per atom - graphite, planar, 3 bonds per atom, layer of delocalised electrons - graphene, 1 layer of graphite, ↑ tensile strength & good conductor of electricity

Question 47

What are the physical properties of ionic structures?

Answer 47

- ↑ m/bp due to giant lattice w/ strong electrostatic forces between oppositely charged ions - soluble in water - poor conductor as solid, good when molten (ions free) - crystalline solids

Question 48

What are the physical properties of simple molecular structures?

Answer 48

- ↓ m/bp due to weak intermolecular forces - generally poor solubility in water - poor conductor as solid & molten (no ions) - mostly gases & liquids

Question 49

What are the physical properties of macromolecular structures?

Answer 49

- ↑ m/bp due to many strong covalent bonds - insoluble in water - diamond poor conductor, graphite good (delocalised) - solids

Question 50

What are the physical properties of metallic structures?

Answer 50

- ↑ m/bp due to strong electrostatic forces - insoluble in water - good conductor as solid & molten - shiny & malleable