4.4.1 - Atoms and Isotopes

Atomic Structure

Give an approximation for the radius of an atom.

1x10^-10 metres

What are the three subatomic constituents of an atom?

1. Proton
2. Neutron
3. Electron

Where is most of the mass of an atom concentrated?

In the nucleus

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

1/10,000

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

The protons and neutrons are found in the atom’s nucleus

The electrons are found in discrete energy levels around the nucleus

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

Positive charge

The nucleus contains protons and neutrons

Protons have a positive charge

Neutrons have no charge

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

1. Absorbing electromagnetic radiation
2. Emitting electromagnetic radiation

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

Electrons move further away from the nucleus

They move to a higher energy level

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

Electrons move closer to the nucleus

They move to a lower energy level

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

The number of protons is equal to the number of electrons

Protons and electrons have equal and opposite charges, so charge cancels

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

They all have the same number protons

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

Atomic number

What is an atom’s mass number?

The total number of protons and neutrons in the atom

What is an isotope of an atom?

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

How do atoms turn into positive ions?

They lose one or more of their outer electrons

Electrons are negatively charged, so the resultant charge of the atom is positive

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

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

How did the plum-pudding model describe the atom?

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

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

The atom was believed to be indivisible

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

Rutherford’s alpha-scattering experiment

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

The Bohr nuclear model

State the conclusions of the Alpha-Scattering experiment.

Most of the mass of the atom is concentrated at the centre in the nucleus

The nucleus is positively charged

What reinforced a scientific theory?

When experimental results agree with the hypothesised theoretical calculations and theories

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

The existence of neutrons