Compare Nucleon, Proton and Neutron Numbers - 2019 P1 Q1

Hi folks, Happy 2020!

In this first video of the year, let's check out Question 1 of 2019 A Level H2 Chemistry Paper 1:

2019 A Level H2 Chem Paper1 Q1 question

We know that:

- proton number or atomic number is the number of protons in the nucleus
- neutron number is the number of neutrons in the nucleus
- nucleon number or mass number is the number of protons and neutrons in the nucleus

So we need to use the information given in the question to deduce the proton number and neutron number of unknown species W, X and Y.

1. Deduce Proton Number

We are given that the species Sr2+, W, X- and Y2- have the same number of electrons.

So from known element strontium which has a proton number of 38, we can deduce Sr2+ has 36 electrons.

This means W, X- and Y2- each has 36 electrons, since they are isoelectronic.

We can then deduce the proton number of each of these species: W-36, X-35 and Y-34.

2019 A Level H2 Chem Paper1 Q1 deduce proton numbers

2. Deduce Neutron Number

We are also given that the isotope of Sr with mass number 84 has the same number of neutrons as the unknown species.

So we can work out the neutron number for Sr which is 46.

2019 A Level H2 Chem Paper1 Q1 deduce neutron numbers

Hence W, X and Y each has 46 neutrons.

3. Deduce Nucleon Number

Finally we can determine the nucleon number for the species which is just adding up the proton and neutron numbers together.

2019 A Level H2 Chem Paper1 Q1 deduce nucleon numbers

Finally we can compare the options and determine the answer to this question is B.

2019 A Level H2 Chem Paper1 Q1 compare options for answer

Topic: Atomic Structure, Physical Chemistry, A Level Chemistry, Singapore

Back to list of questions for 2019 A Level H2 Chemistry Paper 1

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