4.4.1 Atoms and isotopes

Question 1

Give an approximation for the radius of an atom.

Answer 1

1x10^−10 metres

Question 2

What are the three subatomic constituents of an atom?

Answer 2

1. Proton
2. Neutron
3. Electron

Question 3

Where is most of the mass of an atom concentrated?

Answer 3

In the nucleus.

Question 4

Approximately what proportion of the total radius of an atom is the radius of the nucleus?

Answer 4

1/10,000

Question 5

Describe the arrangement of protons, neutrons and electrons in an atom.

Answer 5

● The protons and neutrons are found in the atom’s nucleus
● The electrons are found in discrete energy levels around the nucleus

Question 6

What type of charge does the nucleus of an atom have? Why?

Answer 6

● Positive charge
● The nucleus contains protons and neutrons
● Protons have a positive charge
● Neutrons have no charge

Question 7

Give two ways that an atom’s electron arrangement can be changed.

Answer 7

1. Absorbing electromagnetic radiation 2. Emitting electromagnetic radiation

Question 8

Explain how an atom’s electron arrangement changes when it absorbs EM radiation.

Answer 8

● Electrons move further away from the nucleus
● They move to a higher energy level

Question 9

Explain how an atom’s electron arrangement changes when it emits EM radiation.

Answer 9

● Electrons move closer to the nucleus ● They move to a lower energy level

Question 10

How does the ratio of electrons to protons in an atom result in the atom having no overall charge?

Answer 10

● The number of protons is equal to the number of electrons
● Protons and electrons have equal and opposite charges, so charge cancels

Question 11

What do all forms of the same element have in common?

Answer 11

They all have the same number of protons.

Question 12

What is the name given to the number of protons in an atom?

Answer 12

Atomic number

Question 13

What is an atom’s mass number?

Answer 13

The total number of protons and neutrons in the atom.

Question 14

What is an isotope of an atom?

Answer 14

An atom of an element that has a different number of neutrons, but the same number of protons.

Question 15

How do atoms turn into positive ions?

Answer 15

● They lose one or more of their outer electrons
● Electrons are negatively charged, so the resultant charge of the atom is
positive

Question 16

What may lead to a scientific model being changed or replaced?

Answer 16

The discovery of new experimental evidence which doesn’t agree with the existing theory.

Question 17

How did the plum-pudding model describe the atom?

Answer 17

A ball of positive charge, with negatively charged electrons distributed evenly throughout it.

Question 18

Prior to the discovery of the electron what was believed about the atom?

Answer 18

The atom was believed to be indivisible.

Question 19

Which experiment led to the plum-pudding model being discarded?

Answer 19

Rutherford’s alpha-scattering experiment.

Question 20

What is the name given to the currently accepted model of the atom?

Answer 20

The Bohr nuclear model.

Question 21

State the conclusions of the Alpha-Scattering experiment.

Answer 21

● Most of the mass of the atom is concentrated at the centre in the
nucleus
● The nucleus is positively charged

Question 22

What reinforces a scientific theory?

Answer 22

When experimental results agree with the hypothesised theoretical calculations and theories.

Question 23

What did James Chadwick’s experiments on the atom prove?

Answer 23

The existence of neutrons.