1.
State what is meant by an ionic bond.
[1 mark]
- electrostatic attraction between oppositely charged ions
JD SCIENCE
Unit 2 answers — C2 Elements, compounds and mixtures
Indicative marking points. Award marks for equivalent scientific or mathematical wording. Do not issue this sheet with the student worksheet.
2.
State what is meant by a covalent bond.
[1 mark]
- a shared pair of electrons between atoms
3.
State what is meant by a metallic bond.
[1 mark]
- attraction between positive ions and delocalised electrons
4.
State what is meant by a giant ionic lattice.
[1 mark]
- repeating 3D structure of ions
5.
State what is meant by a simple molecule.
[1 mark]
- small group of atoms with covalent bonds
6.
State what is meant by graphite.
[1 mark]
- giant covalent structure of carbon in layers
7.
State what is meant by graphene.
[1 mark]
- a single layer of graphite
8.
State what is meant by a polymer.
[1 mark]
- a long chain of repeating monomers
9.
State what is meant by a nanoparticle.
[1 mark]
- a particle 1–100 nm in size
10.
State what is meant by an intermolecular force.
[1 mark]
- a force between molecules, weaker than covalent bonds
11.
Grace is asked about an ionic bond in a OCR Chemistry paper.
(a) [2 marks]
- formed by transfer of electrons
(b) [3 marks]
- why ionic compounds have high melting points
12.
Grace is asked about a covalent bond in a OCR Chemistry paper.
(a) [2 marks]
- in molecules and giant covalent structures
(b) [3 marks]
- why diamond is hard
13.
Grace is asked about a metallic bond in a OCR Chemistry paper.
(a) [2 marks]
- in metals
(b) [3 marks]
- why metals conduct electricity
14.
Grace is asked about a giant ionic lattice in a OCR Chemistry paper.
(a) [2 marks]
- e.g. sodium chloride
(b) [3 marks]
- why ionic compounds conduct when molten or dissolved but not as solids
15.
Grace is asked about a simple molecule in a OCR Chemistry paper.
(a) [2 marks]
- weak intermolecular forces between molecules
(b) [3 marks]
- why iodine has a low melting point
16.
Grace is asked about graphite in a OCR Chemistry paper.
(a) [2 marks]
- layers can slide; delocalised electrons
(b) [3 marks]
- why graphite is a lubricant and a conductor
17.
A cube nanoparticle of side 2 nm. Estimate SA:V compared with a 2 m cube (qualitative then ratio idea).
[3 marks]
- SA:V increases as size decreases
- Final answer: SA:V is much larger for the nanoparticle
18.
How many covalent bonds does a carbon atom form in diamond?
[3 marks]
- Final answer: 4
19.
Na has 11 electrons. Write the ion and the electron configuration of Na⁺.
[3 marks]
- loses 1 electron
- Final answer: Na⁺ 2,8
20.
The formula of magnesium chloride. Mg is 2+ and Cl is 1−.
[3 marks]
- balance charges
- Final answer: MgCl₂
21.
A polymer repeat unit is C₂H₄. What is the empirical formula?
[3 marks]
- Final answer: CH₂
22.
Rf = distance spot / distance solvent. Spot 3.6 cm, solvent 6.0 cm. Rf?
[3 marks]
- Final answer: 0.60
23.
Grace carries out melting-point comparison of ionic vs simple molecular substances. This is a typical OCR required-practical style question.
(a) [2 marks]
- Independent: substance type
- Dependent: melting temperature
(b) [2 marks]
- same heating method
- so the test is fair / only one variable is changed
(c) [2 marks]
- uneven heating
24.
Grace carries out testing electrical conductivity of solid, molten and dissolved samples. This is a typical OCR required-practical style question.
(a) [2 marks]
- Independent: state of sample
- Dependent: whether the bulb lights
(b) [2 marks]
- same voltage
- so the test is fair / only one variable is changed
(c) [2 marks]
- electrodes not clean
25.
Grace carries out building ball-and-stick models of CH₄, H₂O, CO₂, NaCl. This is a typical OCR required-practical style question.
(a) [2 marks]
- Independent: substance
- Dependent: correct geometry
(b) [2 marks]
- same modelling kit
- so the test is fair / only one variable is changed
(c) [2 marks]
- wrong number of bonds
26.
Grace carries out chromatography to identify a mixture of dyes. This is a typical OCR required-practical style question.
(a) [2 marks]
- Independent: dye
- Dependent: Rf
(b) [2 marks]
- same solvent
- so the test is fair / only one variable is changed
(c) [2 marks]
- solvent front marked after it evaporates
27.
Compare ionic bonding with covalent bonding.
[4 marks]
- ionic: transfer, metals + non-metals
- covalent: sharing, non-metals
28.
Compare diamond with graphite.
[4 marks]
- diamond: 3D tetrahedral, insulator, hard
- graphite: layers, conductor, soft
29.
Compare a metal with an ionic solid.
[4 marks]
- both high MP
- metal: malleable, conducts as solid; ionic: brittle, conducts when molten
30.
Compare simple molecular with giant covalent.
[4 marks]
- simple: low MP, weak intermolecular forces
- giant: high MP, many strong covalent bonds
31.
Apply your knowledge of graphene to this situation: conducts and is very thin
[3 marks]
- conducts and is very thin
32.
Apply your knowledge of a polymer to this situation: cross-links
[3 marks]
- cross-links