4.1 Atoms and Isotopes

Question 1

give an approximation for the radius of an atom.

Answer 1

1 x 10^-10 metres

Question 2

what type of charge does the nucleus of an atom have? why?

Answer 2

• positive charge
• the nucleus contains protons and neutrons
• protons have a positive charge
• neutrons have no charge

Question 2

where is most of the mass of an atom concentrated?

Answer 2

in the nucleus.

Question 2

what are the three subatomic constituents of an atom?

Answer 2

1. proton
2. neutron
3. electron

Question 3

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

Answer 3

1/10,000

Question 3

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

Answer 3

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

Question 4

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

Answer 4

• electrons move closer to the nucleus
• they move to a lower energy level

Question 4

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

Answer 4

1. absorbing electromagnetic radiation
2. emitting electromagnetic radiation

Question 5

explain how an atom’s electron arrangment changes when it absorbs EM radiation.

Answer 5

• electrons move further away from the nucleus
• they move to a higher energy level

Question 6

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

Answer 6

they all have the same number of protons.

Question 6

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

Answer 6

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

Question 7

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

Answer 7

atomic number

Question 8

what is an atom’s mass number?

Answer 8

the total number of protons and neutrons in the atom.

Question 9

what is an isotope of an atom?

Answer 9

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

Question 10

how do atoms turn into positive ions?

Answer 10

• they lose one or more of their outer electrons
• electrons are negatively charged, so the resultant charge of the atom is positive

Question 11

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

Answer 11

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

Question 12

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

Answer 12

the atom was believed to be indivisible.

Question 12

how did the plum-pudding model describe the atom?

Answer 12

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

Question 13

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

Answer 13

rutherford’s alpha-scattering experiment.

Question 14

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

Answer 14

the bohr nuclear model.

Question 15

state the conclusions of the alpha-scattering experiment.

Answer 15

• most of the mass of the atom is concentrated at the centre in the nucleus
• the nucleus is positively charged

Question 16

what reinforces a scientific theory?

Answer 16

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

Question 17

what did james chadwick’s experiments on the atom prove?

Answer 17

the existence of neutrons.