SC1: Key concepts

Question 1

What are the three ideas in John Dalton’s theory about the atom?

Answer 1

1. Atoms cannot be created, divided or destroyed.
2. Atoms of the same element are exactly the same and atoms of different elements are different.
3. Atoms join with other atoms to make new substances.

Question 2

What discovery caused the original Dalton model of the atom to change?

Answer 2

The discovery of subatomic particles.

Question 3

How did JJ Thomson discover the electrons?

Answer 3

Thomson experimented with a cathode (negatively charged) ray tube. The beam moved towards the positively charged plate so he knew that the particles must have a negative charge

Question 4

Describe the atomic model proposed by JJ Thomson.

Answer 4

Plum pudding model. Negative charges scattered through a dough of positive charge.

Question 5

What did Ernest Rutherford discover from his gold foil experiment?

Answer 5

He found out that most of the atom is empty space since most of the positively charged particles went straight through. A few particles were deflected slightly and a few were deflected at an angle greater than 90° suggesting that there is a positively charged nucleus in the centre.

Question 6

Describe Rutherford’s new model of the atom.

Answer 6

Mass and positive charge is concentrated in the centre in the nucleus. Most of the atom is empty space. Electrons are in orbits around the nucleus.

Question 7

Describe the structure of atoms.

Answer 7

Small dense nucleus in the centre made up of protons and neutrons. Electrons orbit the nucleus in shells.

Question 8

What are the relative masses of protons, neutrons and electrons?

Answer 8

Proton: 1
Neutron: 1
Electron: 1/1835 (negligible)

Question 9

What are the relative charges of protons, neutrons and electrons?

Answer 9

Proton: +1
Neutron: 0
Electron: -1

Question 10

Why do atoms contain equal numbers of protons and electrons?

Answer 10

Atoms are stable with no overall charge. Protons are positively charged and electrons are negatively charged. For the charge to be 0 overall there must be equal number of protons and electrons that cancel each other out.

Question 11

Where is the mass of an atom concentrated?

Answer 11

In the nucleus.

Question 12

What does the atomic number of an atom represent?

Answer 12

The number of protons in the nucleus.

Question 13

What does the mass number of an atom tell you?

Answer 13

The mass number is the number of protons and neutrons found in the nucleus.

Question 14

What is an isotope?

Answer 14

Isotopes are atoms with the same proton number (proton number identifies the element so same element) but different neutron number.

Question 15

Boron has the atomic number of 5 and the mass number of 11. How many protons, electrons and neutrons does Boron have?

Answer 15

5 protons
5 electrons
6 neutrons (11-5)