1.
State what is meant by an atom.
[1 mark]
- the smallest part of an element that can exist
JD SCIENCE
Unit 1 answers — The nature of substances and chemical reactions
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 proton.
[1 mark]
- positive particle in the nucleus, mass 1, charge +1
3.
State what is meant by a neutron.
[1 mark]
- neutral particle in the nucleus, mass 1
4.
State what is meant by an electron.
[1 mark]
- negative particle in shells, almost no mass, charge −1
5.
State what is meant by an isotope.
[1 mark]
- atoms of the same element with different numbers of neutrons
6.
State what is meant by the periodic table.
[1 mark]
- arrangement of elements in atomic number order
7.
State what is meant by a Group 1 metal.
[1 mark]
- alkali metal with one outer electron
8.
State what is meant by a Group 7 element.
[1 mark]
- halogen with seven outer electrons
9.
State what is meant by a mixture.
[1 mark]
- two or more substances not chemically combined
10.
State what is meant by a compound.
[1 mark]
- two or more elements chemically combined
11.
Owain is asked about an atom in a WJEC Chemistry paper.
(a) [2 marks]
- nucleus of protons and neutrons, electrons in shells
(b) [3 marks]
- why atoms are neutral
12.
Owain is asked about a proton in a WJEC Chemistry paper.
(a) [2 marks]
- atomic number is the number of protons
(b) [3 marks]
- why elements are different
13.
Owain is asked about a neutron in a WJEC Chemistry paper.
(a) [2 marks]
- isotopes have different numbers of neutrons
(b) [3 marks]
- why isotopes have the same chemistry
14.
Owain is asked about an electron in a WJEC Chemistry paper.
(a) [2 marks]
- arranged 2,8,8
(b) [3 marks]
- why Group 1 reacts similarly
15.
Owain is asked about an isotope in a WJEC Chemistry paper.
(a) [2 marks]
- same atomic number, different mass number
(b) [3 marks]
- why relative atomic mass is not a whole number
16.
Owain is asked about the periodic table in a WJEC Chemistry paper.
(a) [2 marks]
- groups and periods
(b) [3 marks]
- why Mendeleev left gaps
17.
An atom has 15 protons and 27 neutrons. Write the mass number and atomic number.
[3 marks]
- mass number = protons + neutrons
- Final answer: mass number 42, atomic number 15
18.
Calculate the relative atomic mass of an element with 75% isotope 35 and 25% isotope 37.
[3 marks]
- (75×35 + 25×37)/100
- Final answer: 35.5
19.
How many electrons are in a 15+ ion of this element if it is in Group 1?
[3 marks]
- lost 1 electron
- Final answer: 14
20.
A shell holds 2n² electrons. How many in the 3rd shell?
[3 marks]
- 2×9
- Final answer: 18
21.
20 g of carbon-12 contains 1 mole. How many atoms?
[3 marks]
- Avogadro
- Final answer: 6.02 × 10²³
22.
Write the electronic structure of an element with 17 electrons.
[3 marks]
- chlorine
- Final answer: 2,8,7
23.
Owain carries out the flame-test practical for metal ions. This is a typical WJEC required-practical style question.
(a) [2 marks]
- Independent: metal ion
- Dependent: flame colour
(b) [2 marks]
- clean wire, same flame
- so the test is fair / only one variable is changed
(c) [2 marks]
- contaminated wire
24.
Owain carries out paper chromatography of inks. This is a typical WJEC required-practical style question.
(a) [2 marks]
- Independent: ink / solvent
- Dependent: Rf value
(b) [2 marks]
- same solvent front measurement
- so the test is fair / only one variable is changed
(c) [2 marks]
- spot below the solvent level
25.
Owain carries out separating rock salt (sand and salt). This is a typical WJEC required-practical style question.
(a) [2 marks]
- Independent: n/a
- Dependent: mass of salt recovered
(b) [2 marks]
- same method
- so the test is fair / only one variable is changed
(c) [2 marks]
- loss on transfer / incomplete evaporation
26.
Owain carries out investigating the reaction of Group 1 metals with water (demonstration). This is a typical WJEC required-practical style question.
(a) [2 marks]
- Independent: metal
- Dependent: observations / time
(b) [2 marks]
- same size piece
- so the test is fair / only one variable is changed
(c) [2 marks]
- oxide layer / not a fair size
27.
Compare an element with a compound.
[4 marks]
- element: one type of atom
- compound: bonded atoms of different elements
28.
Compare Group 1 with Group 7.
[4 marks]
- Group 1 lose 1 electron, metals
- Group 7 gain 1 electron, non-metals
29.
Compare a mixture with a compound.
[4 marks]
- mixture: not chemically combined, easier to separate
- compound: fixed composition
30.
Compare the plum-pudding model with the nuclear model.
[4 marks]
- plum pudding: sphere of positive charge with electrons
- nuclear: tiny positive nucleus, electrons outside
31.
Apply your knowledge of a Group 1 metal to this situation: outer electron is further / more shielding
[3 marks]
- outer electron is further / more shielding
32.
Apply your knowledge of a Group 7 element to this situation: chlorine is more reactive
[3 marks]
- chlorine is more reactive