# Exam-style Questions: Atomic Structure

1. In the following nuclear equation, identify the nucleon and atomic numbers for the element Y. • Nucleon number: 35, Atomic number: 95
• Nucleon number: 95, Atomic number: 35
• Nucleon number: 96, Atomic number: 35
• Nucleon number: 35, Atomic number: 96

You need to check that the numbers at the top are the same on both sides and that the numbers on the bottom are the same at both sides.

There are two possible tricks here.

First: remember that the nucleon number is the number of protons and neutrons added together - so it is the bigger of the two numbers. The atomic number is the number of protons.

Secondly: don't forget that there are two neutrons on the right hand side. That means that the total value of the nucleon number on the right hand side excluding Y is 139 + 2x1 = 141.

2. a) Outline briefly the experimental evidence by an x-particle scattering experiment for

i) An atom containing a very small nucleus.

(2 marks)

ii) The nucleus being charged.

(2 marks)

b) Name the effect which enables the following to be measured.

i) Spacing between atoms in crystals

(1 mark)

(2 marks)

(Marks available: 7)

Answer outline and marking scheme for question: 1

a) most alphas have small deflection

so nucleus is small target to be gravitational

so must be electrostatic i.e charged

(4 marks)

b) X-ray diffraction or neutron diffraction

high energy

electron scattering

(3 marks)

(Marks available: 7)

3. a) Complete this table summarising the properties of the proton, electron and neutron

(4 marks)

b) The element sodium can be represented as:

i) What is the name of the top number

(1 mark)

ii) Calculate the number of protons, neutrons and electrons in an atom of sodium.

(3 marks)

iii) Complete the list below by selecting from these numbers :

1 x 10 -14m

2 x 10 -10m

2 x 10 -14m

1 x 10 -10m

Length of oxygen molecule =

(3 marks)

(Marks available: 11)

Answer outline and marking scheme for question: 2

a)

(4 marks)

b) i) Nucleon number 7

(1 mark)

ii) Protons = 11 Neutrons = 12 Electrons = 11

(3 marks)

iii) Radius of oxygen nucleus = 1 x 10 14m

Radius of oxygen atom = 1 x 10 -10m

Length of oxygen molecule = 2 x 10 -10m

(3 marks)

(Marks available: 11)

4. The radius r of a nucleus is related to its mass number A by the equation.

r = r0A1/3

where r0 is a constant.

a) On Fig. 1.1, sketch a graph of r against A. (2 Marks)

b) State the significance of r0.

(1 Mark)

c) An oxygen nucleus consists of 8 protons and 8 neutrons, Its radius is 3.53 x 10-15 m.

Show that r0 is 1.4 x 10-15 m.

(1 Mark)

(Marks available: 4)

Answer outline and marking scheme for question: 3

a) graph: curved, incorrect sense

starts at origin and eventually approaches horizontal

(straight line scores zero)

(2 Marks)

b) r0 is radius of 1 proton / neutron/ nucleon / hydrogen nucleus

(not nucleus / nuclei/ atom/ molecule)

(1 Mark)

c) r0 = r / A1/3 = 3.53 x 10-15 / 161/3

( = 1.4 x 10-15 ) m

(1 Mark)

(Marks available: 4) 