1.1 A simple model of the atom, symbols, relative atomic mass, electronic charge and isotopes

Question 1

What are all substances made of ?

Answer 1

All substances are made of tiny particles called atoms

Question 2

Define the term ‘atom’

Answer 2

Atoms are tiny, indivisible particles that all substances are made up of and the smallest part of an element that can exist

Question 3

Define the term ‘element’

Answer 3

An element is a pure substance that is made of only one sort of atom which cannot be chemically broken down into simpler substances

Question 4

Define the term ‘pure’

Answer 4

Pure means it is made up of one type of substance.

Question 5

Define the term ‘molecule’

Answer 5

A molecule is a group of two or more atoms joined together by covalent bonds

Question 6

Define the term ‘compound’

Answer 6

A compound is pure substance that contain two or more elements chemically combined in fixed proportions

Question 7

Define the term ‘mixture’

Answer 7

A mixture consists of two or more elements or compounds not
chemically combined together

Question 8

Which physical processes can separate mixtures ?

Answer 8

filtration, crystallisation, simple distillation, fractional distillation and
chromatography

Question 9

What was the first concept about the atom ?

Answer 9

Democritus had the 1st atomic theory about particles and atoms - he thought matter was made up of millions of tiny, uncuttable pieces of that same matter

Question 10

What was the second concept about the atom ?

Answer 10

The atoms were tiny spheres that were indivisible - J.D. SportS (John Dalton Solid Sphere)
- all matter made of atoms
- atoms can’t be broken down into anything simpler
- atoms are rearranged in chemical reaction

Question 11

What was the third concept about the atom ?

Answer 11

The atom was a ball of positive charge with negative electrons embedded in it - J.J. Thomson’s Plum Pudding Model

Thomson was experimenting by applying high voltages to gases at low temperatures.
He did experiments on the beams of particles.
The particles were attracted to a positive charge, showing the particles must be negatively charged.
Therefore, these electrons must have come from inside the atoms in the tube.
Leading to Dalton’s idea that atoms cannot be divided had to be revised

Question 12

Which model replaced the Plum Pudding Model ?

Answer 12

The Nuclear Model by Ernest Rutherford replaced the Plum Pudding Model

Question 13

What was the fourth concept about the atom ?

Answer 13

Ernest Rutherford - The mass of an atom was concentrated at the
nucleus and that the nucleus was charged.

Question 14

Which experiment lead to the mass of the atom concentrated at nucleus and it was charged ?

Answer 14

This is due to the results from the alpha particle scattering experiment led to this conclusion.

Question 15

Describe and explain the Gold foil experiment (alpha scattering)

Answer 15

Experiment was carried out by his assistants: Geiger and Marsden

A beam of alpha particles (dense positively charged particles) was aimed at very thin gold
Their passage through the foil was detected
The scientists expected the alpha particles to pass through the foil with their diffuse cloud of positive charge but there were unexpected results
Some of alpha particles were deflected from the foil at different angles and some came straight back.
The scientists realised that the positively charged alpha particles were being repelled and deflected by a tiny concentration of positive charge in the nucleus of the atom.

As a result of this experiment, the plum pudding model was replaced by the nuclear model of the atom.

Question 16

How did the gold foil experiment disprove Thomson’s plum pudding model ?

Answer 16

Rutherford suggested Thomson’s atomic model was not possible.
The positive charge must be concentrated at centre (nucleus) of the atom.
Otherwise the large positive particles fired at the foil could never be repelled back towards their source.
It was proposed that the electrons must be orbiting the nucleus, which contain dense positively charged electrons

Question 17

State two ways Rutherford changed Thomson’s model of the atom

Answer 17

Electrons orbit nucleus
At centre there’s positively charged nucleus

Question 18

What were the conclusions reached by Rutherford in Alpha scattering experiment ?

Answer 18

1 . Atoms have lots of empty space
2 . At centre there’s positively charged nucleus
3 . Most of the mass is concentrated at the centre (nucleus)

Question 19

How did the unexpected results of Geiger and Marsden’s experiment (Gold Foil) lead to the theory of a nuclear atom ?

Answer 19

The early plum pudding model was a sphere of positive charge with negative electrons embedded in it. An experiment was carried out to prove this plum pudding model of the atom but the results were unexpected.

Question 20

What was the fifth concept about the atom ?

Answer 20

Niels Bohr adapted the nuclear model by suggesting that electrons
orbit the nucleus at specific distances ( rather than embedded in positive charge ).
Bohr’s theoretical calculations agreed with experimental observations.

He suggested that electrons travel around nucleus of an atom in orbits or definite paths
Depending on their energy, electrons can jump from one energy level another energy level

Question 21

What’s the difference between the plum pudding model of the atom and the nuclear model of the atom ?

Answer 21

nuclear model mass is concentrated at the nucleus (1)

plum pudding model mass is evenly distributed (1)

nuclear model positive charge occupies only a small part of the atom (1)

plum pudding model positive charge spread throughout the atom (1)

nuclear model electrons orbit some distance from the nucleus (1)

plum pudding electrons embedded in the (mass) of positive (charge) (1)

nuclear model the atom mainly empty space (1)

plum pudding model is a ‘solid’ mass (1)

Question 22

What did later experiments after Bohr’s observations lead to ?

Answer 22

Later experiments led to the idea, the positive charge of any
nucleus could be subdivided into a whole number of smaller
particles.
Each particle has the same amount of positive charge.
The particles were called protons.

Question 23

What was sixth concept about the atom ?

Answer 23

Around 20 years after the nucleus became an accepted scientific
idea,
James Chadwick’s experimental work provided evidence
to show the existence of neutrons within the nucleus.

Question 24

What did James Chadwick do ?

Answer 24

Realized that atomic mass of most elements was double the number of protons

This lead to discovery of the neutron

He did an experiment that could only be explained by the existence of neutrons

Question 25

Explain how Chadwick’s work led to better understanding of isotopes understanding

Answer 25

Chadwick provided evidence to show the existence of
neutrons
This was necessary because isotopes have the same number of protons but with different number of neutrons

Question 26

What is the development of the theory of atomic structure an example of ?

Answer 26

How a theory may change as new evidence is found
How scientific evidence is provisional but may become more convincing when predictions based on it are confirmed later on

Question 27

What is the order of subatomic particles by discovery ?

Answer 27

(shape, electrons), nucleus, protons, shells, neutrons

Question 28

State the relative charge of the sub-atomic particles

Answer 28

Proton = +1
Neutron = 0
Electron = -1

Question 29

Why do atoms have to overall (electrical) charge ?

Answer 29

The number of electrons is equal to the number of
protons in the nucleus therefore the charges cancel out.

Question 30

What is the atomic number of an atom ?

Answer 30

The number of protons in an atom of an element

Question 31

Why does the nucleus have a positive charge ?

Answer 31

The nucleus is positively charged as protons are positively charged and neutrons have no charge which result in an overall positive charged nucleus.

Question 32

Use the nuclear model to describe atoms

Answer 32

In nuclear model:
at the centre positive charge occupies the nucleus
mass is concentrated at the nucleus
positive charge occupies only a small part of the atom
most of the atom is empty space

Question 33

What is radius of an atom ?

Answer 33

Atoms have a radius of about 0.1 nm (1 x 10-10 m)

Question 34

What is radius of a nucleus ?

Answer 34

Radius of a nucleus is less than 1/10 000 of the atom
- about 1 x 10-14 m

Question 35

State the relative mass of the sub-atomic particles

Answer 35

Proton = 1
Neutron = 1
Electron = very small ( 1/2000 )

Question 36

Define the term ‘mass number’

Answer 36

The sum of protons and neutrons in nucleus of a given atom

Question 37

Define the term ‘isotope’

Answer 37

Atoms of the same element with same number of protons but different number of neutrons

Question 38

What is Relative atomic mass ( Ar ) ?

Answer 38

Ar is average value that takes account of the abundance of the isotopes of the element

Question 39

Relative atomic mass ( Ar ) formula

Answer 39

Relative atomic mass (Ar) = sum of (isotope abundance x isotope mass number) / 100

Question 40

What term do you use (instead of mass number) when referring to the element as a whole ?

Answer 40

The relative atomic mass is used when referring to the element as a whole

Question 41

Where do electrons occupy in an atom ?

Answer 41

Electrons in an atom occupy the lowest available energy levels
(innermost available shells)

Question 42

Which shell has the highest energy level
(1st, 2nd, 3rd shell)

Answer 42

The third shell has highest energy level.

Question 43

What does the period number tell you ?

Answer 43

In periodic table, period number is equivalent to the number of electron shells an atom contains

Question 44

What does the group number tell you ?

Answer 44

In periodic table, group number shows the number electrons an atom has in it’s outer most shell.
Group number also tells you the charge on an atom