4.1 ATOMS AND ISOTOPES

Question 1

Give an approximation for the radius of an atom

Answer 1

1 x 1^-10 m

Question 2

What are the three subatomic constituents of an atom

Answer 2

proton
neutron
electron

Question 3

Where is most of the mass in 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.