1.1 A simple model of the atom & symbols

Question 1

What is an atom?

Answer 1

An atom is the smallest part of an element that can exist

Question 2

What is an element?

Answer 2

An element is a substance of only one type of atom

Question 3

How are the elements listed and approximately how many are there?

Answer 3

They are listed in the periodic table and there are approximately 100

Question 4

Elements may combine through chemical reactions to form new products; what are
these new substances called?

Answer 4

Compounds

Question 5

What is a compound?

Answer 5

Two or more elements combined chemically in fixed proportions which can be represented by formulae

Question 6

Do compounds have the same properties as their constituent elements?

Answer 6

No, they have different properties.

Question 7

Describe the plum-pudding model

Answer 7

The atom is a ball of positive charge with negative electrons randomly placed in it.

Question 8

Describe the Bohr / nuclear model and how it came about

Answer 8

The nuclear model suggests that electrons orbit the nucleus at specific
distances (shells) – it came about after Rutherford’s alpha scattering experiment

Question 9

Later experiments led to the discovery of smaller, positive
particles in the nucleus; what are
these particles called?

Answer 9

Protons

Question 10

Who discovered the neutron? What year?

Answer 10

James Chadwick, 1932

Question 11

Describe the structure of an
atom

Answer 11

The atom has a small central nucleus (made up of protons and neutrons) around which there are electrons

Question 12

What is the radius of an atom?

Answer 12

0.1 nm

Question 13

What is the radius of a nucleus and
what is it compared to that of the atom?

Answer 13

1 x 10^-14 m and 1/10000

Question 14

What name is given to the
number of protons in the nucleus?

Answer 14

Atomic number

Question 15

Atoms of the same element have the same number of which particle in the nucleus?

Answer 15

Protons

Question 16

Where is the majority of the mass of an atom?

Answer 16

The nucleus

Question 17

How do you calculate the
number of neutrons using mass number and atomic number?

Answer 17

Subtract the atomic number from the mass number

Question 17

What is the mass number?

Answer 17

The total number of protons and neutrons

Question 18

Atoms of the same element have the same number of which particle in the nucleus?

Answer 18

Protons

Question 19

What is an isotope? Do isotopes of a certain element have the same chemical properties?

Answer 19

Atoms of the same element (same proton number) that have a different number of neutrons.

They have the same chemical properties as they have the same electronic structure

Question 20

Who discovered the electron? What year?

Answer 20

J.J. Thomson, 1897

Question 21

Who proposed the plum pudding model?

Answer 21

J.J. Thomson

Question 22

Who discovered the proton? What year?

Answer 22

Ernest Rutherford, 1917

Question 23

Who proposed the nuclear model?

Answer 23

Ernest Rutherford

Question 24

Who proposed the planetary model?

Answer 24

Niels Bohr

Question 25

Who discovered electron shells? What year?

Answer 25

Niels Bohr, 1913

Question 26

Who theorised atoms? What year?

Answer 26

Democritus, 500 BC

Question 27

What was Rutherford’s alpha scattering experiment?

Answer 27

In 1905, Ernest Rutherford conducted an experiment to test the plum pudding model. He directed a beam of alpha particles at a very thin gold leaf suspended in a
vacuum.

-Most of the alpha
particles did pass
straight through
the foil

-A small number of
alpha particles
were deflected by
large angles (> 4°)
as they passed
through the foil

-A very small
number of alpha
particles came
straight back off
the foil
.

Question 28

What was concluded after Rutherford’s alpha scattering experiment?

Answer 28

The fact that most alpha particles went straight through the foil is evidence for the atom being mostly empty space

A small number of alpha particles being deflected at large angles suggested that there is a concentration of positive charge in the atom - like charges repel, so the positive alpha particles were being repelled by positive charges

The very small number of alpha particles coming straight back suggested that the positive charge and mass are concentrated in a tiny volume in the atom (the nucleus)

Question 29

Why was a vacuum used in Rutherford’s alpha scattering experiment?

Answer 29

The vacuum is important because any deflection of the alpha particles would only be because of collisions with the gold foil and not due to deflections off anything else.

Question 30

Why was gold foil used in Rutherford’s alpha scattering experiment?

Answer 30

Gold was used because it was the only metal that could be rolled out to be very, very thin without cracking.