AQA Bonding Chem Questions, Bonding Mark scheme

(e) Sulfur(IV) oxide reacts with water to form a solution containing ions. Write an equation for this reaction.

(e) SO2 + H2O → H+ + HSO3 - Products must be ions Allow SO2 + H2O → 2H+ + SO3 2- Allow two equations showing intermediate formation of H2SO3 that ends up as ions Ignore state symbols Allow multiples

A hydrogen peroxide molecule can be represented by the structure shown. (a) Suggest a value for the H−O−O bond angle.

94−105.5°

Aluminium chloride has a relative molecular mass of 267 in the gas phase. Deduce the formula of the aluminium compound that has a relative molecular mass of 267

Al2Cl6 or AlBr3

State the element in Period 3 that has the highest first ionisation energy. Explain your answer.

Argon - largest no. of protons for same amount of shielding

Explain why CaO melts at 2973K but NaCl melts at 2074K

CaO = Stronger ionic attraction NaCl = Weaker force of attraction

Q4.Which of these atoms has the highest electronegativity? A) Na B) Mg C) Cl D) Ar

Cl

(c) Suggest the element in Period 3 that has the highest electronegativity value.

Cl (Chlorine with 17 protons is the most electronegative element. You might expect argon (with 18 electrons) to be the most electronegative element in Period 3, but its outer energy levels are full. Therefore, it does not form covalent bonds with other atoms, so it is given an electronegativity value of zero.)

A molecule of NHF2 reacts with a molecule of BF3 as shown in the following equation. NHF2 + BF3 ➜ F2HNBF3 State the type of bond formed between the N atom and the B atom in F2HNBF3 Explain how this bond is formed

Covalent bond They share electrons + also a dative bond Dative covalent bond - both e- on N donated to B

BF3 is a covalent molecule that reacts with an F- ion to form a BF4 - ion.Name the type of bond formed when a molecule of BF3 reacts with an F- ion.Explain how this bond is formed.

Dative covalent bond - lone pair of e- from F is donated to B(F3)

Phosphorus is in the same group of the Periodic Table as nitrogen. A molecule of PH3 reacts with an H+ ion to form a PH4 + ion. Name the type of bond formed when PH3 reacts with H+ and explain how this bond is formed.

Dative, lone pair donated from P to H

Explain, in terms of electronegativity, why the boiling point of H2S2 is lower than H2O2.

Electronegativity of S lower than O or electronegativity difference between H and S is lower Mark independently 1 No hydrogen bonding between H2S2 molecules Or only van der Waals / only dipole-dipole forces between H2S2 molecules 1 If breaking covalent bonds CE = 0

Give the formula of the species in a sample of solid phosphorus(V) oxide. State the structure of, and describe fully the bonding in, this oxide.

Formula: P4O10 Mention of ionic or metallic, can score M1 only 1 Structure: Molecular If macromolecular, can score M1 & M3 only 1 Bonding: Covalent / shared electron pair 1 van der Waals' / dipole-dipole forces between molecules Allow vdW, imf and dipole-dipole imf but do not allow imf alone

State the structure of, and bonding in, silicon dioxide. Other than a high melting point, give two physical properties of silicon dioxide that are characteristic of its structure and bonding.

Hard/ Brittle / not malleable Insoluble Non conductor

Explain why the melting point of Mg is higher than that of sodium

Has more delocalised electrons so stronger force of attraction

(d) Why is graphite soft?

Has planes Weak vdw forces entre planes

Explain why the melting point of potassium is lower than that of sodium

However, since potassium has a larger ionic radius than sodium, the attraction between the valence electron and the nucleus is weaker, so it is easier to overcome those forces to change potassium's state from liquid to gas.

Suggest why the melting point of sodium iodide is lower than the melting point of sodium bromide.

Iodide / I- bigger (ion) (so less attraction to the Na+ ion)

Sugggest why the melting point of sodium iodide is lower than the melting point of sodium bromide (?)

Iodide ion is larger than bromide ion Ions are further apart in the iodide

State the type of bonding in lithium fluoride. Explain why a lot of energy is needed to melt a sample of solid lithium fluoride.

Ionic If not ionic then CE = 0 / 3 If blank lose M1 and mark on 1 Strong or many or lots of (electrostatic) attractions (between ions) If molecules / IMF / metallic / atoms lose M2 + M3, penalise incorrect ions by 1 mark 1 Between + and − ions / between Li+ and F− ions / oppositely charged ions

The heat energy needed to vaporise one mole of sodium chloride (171 kJ mol-1) is much greater than the heat energy required to melt one mole of sodium chloride. Explain why this is so.

It must break ALL the bonds to vaporise

(iv) Explain why nickel is ductile (can be stretched into wires).

Layers / planes / sheets of atoms or ions can slide over one another

Strontium metal is used in the manufacture of alloys. (i) Explain why strontium has a higher melting point than barium.

M1 delocalised electrons closer to cations/positive ions/atoms/nucleus cations/positive ions/atoms are smaller cation/positive ion/atom or it has fewer (electron) shells/levels M2 (Sr) has stronger attraction between the cations/positive ions/ atoms/nucleus and the delocalised electrons OR stronger metallic bonding (assume argument refers to Sr but accept converse argument for Ba)

(b) Explain why magnesium has a higher melting point than sodium.

Mg2+ / magnesium ion has higher charge than Na+ Allow Mg2+ ions smaller / greater charge density than Na+ ions Allow Mg atoms smaller than Na (atoms) Allow magnesium has more delocalised electrons Attracts delocalised / free / sea of electrons more strongly / metal-metal bonding stronger / metallic bonding stronger

Suggest why the electronegativity of the elements increases from lithium to fluorine.

More protons / bigger nuclear charge 1 Same or similar shielding / electrons in the same shell or principal energy level / atoms get smaller

Explain why the melting point of sodium iodide (920K) is lower than NaBr (1020K)

Reactivity decreases as you go down the halogen group. This is because when you go down the halogen group, you add another shell of electrons and increase the amount of electron shielding. So the valence electrons feel less of a pull from the nucleus, and are not tightly bound So, Br is more reactive than Na, because Br .

State the element in Period 3 that has the highest melting point. Explain your answer.

Si coz covalent bonds - strong - need lots of J to break Si in a tetrahedral macromolecular structure & it's a giant covalent structure

Deduce the name or formula of a compound that has the same number of atoms, the same number of electrons and the same shape as the AlCl4 − ion.

Sillicon tetrachloride

Deduce why the bonding in nitrogen oxide is covalent rather than ionic.

Small electronegativity difference / difference = 0.5 Must be comparative Allow 2 non-metals

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)

Solvent has low bp or weak intermolecular forces or evaporates quickly (1) (Solvent) needs energy to evaporate (to overcome intermolecular forces) (1) OR higher energy or faster molecules more likely to escape so mean energy (and hence temperature) falls Energy taken from the skin (and so it cools) (1) Fragrance or perfume (molecules) slowly spreads (through the room) (1) By random movement or diffusion (of the perfume / fragrance) (1)

(ii) Write an equation for the reaction of strontium with water.

Sr + 2H2O → Sr(OH)2 + H2

(ii) Explain why the melting point of sodium chloride is high.

Strong (electrostatic) attraction Any mention of IMF or molecules / metallic / covalent in (b)(ii) then CE 0/2 1 Between oppositely charged ions / particles

Explain why electronegativity increases across a period in the Periodic Table

The no. of protons increases across a period and the atomic radius of the atom of an element decreses across period Greater nuclear charge Greater attraction between positive nucleus & outer electrons Size of atom of an element decreases as you go across a period

Use the values in the table to explain how the strongest type of intermolecular force arises between two molecules of ammonia.

There is a large electronegativity entre H & N They form N delta neg & H delta pos Lone pair on N forms weaks bonds with H delta pos

Explain why the TlCl2 + ion has the shape that you have drawn in part (f)(i)

They repel equally + no lone pairs so its linear

Explain, in terms of its structure and bonding, why titanium has a high melting point (2 marks)

Titanium has strong metallic bonding strong electrostatic force of attraction entre delocalised electrons & positive titanium ions Lots of J needed to break metallic bonding + forces of attraction

Give one reason why ice is less dense than water

as the water molecules are more spread out due to H-bonding

i) Why is it a little surprising, at first sight, that the N-N bond is weaker than the P-P bond? ii) Explain this apparent anomaly

i) N is smaller than P, electrons are held close together qui causes repulsion from the lone pairs on each ii) N has weaker bond strength

In terms of electrons, explain why an arrow is used to represent this N→H bond.

it shows the pair of e- comes from nitrogen