Atoms and Isotopes

Give an approximation for the radius of an atom

1 × 10^-10 metres

What are three subatomic constituents of an atom?

proton, neutron, electron

Where is the most mass of an atom concentrated?

In the nucleus

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

1/10,000

Describe the arrangements of protons, neutrons and electrons in an atom

• Protons and neutrons are found in the atoms’s nucleus

• Electrons are found in discrete energy levels around the nucleus

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

• Positive charge

• Nucleus contains protons and neutrons

• Protons have a positive charge

• Neutrons have no charge

Give two ways that an atoms electron arrangement can be changed

Absorbing electromagnetic radiation and emitting electromagnetic radiation

Explain how an atoms electron arrangement changes when it absorbs EM radiation

• Electrons move further away from the nucleus

• Try move to a higher 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 of protons

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

Atomic number

What is an atoms 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 being discharged?

Rutherford’s alpha scattering experiment

What is the name given to the currently accepted model of an 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 reinforces a scientific theory?

When experimental results agree with the hypothesised calculations and theories

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

The exsistence of neutrons