Atomic Structure And Isotopes

Question 1

Who developed the first idea of the atom?

Answer 1

Democritus

Question 2

What did Democritus suggest?

Answer 2

Can divide a sample of matter only so many times, eventually you would end up with a particle that cannot be split any further

Question 3

What were John Dalton’s 3 predictions about atomic theory?

Answer 3

1) Atoms are tiny particles that make up elements
2) Atoms cannot be divided
3) Atoms of an element are different to those of every other element

Question 4

What did John Dalton do?

Answer 4

Used symbols to represent atoms of different elements and developed the first table of atomic masses

Question 5

What is a positive about John Dalton?

Answer 5

Most of his predictions still hold true today

Question 6

What did Thompson do?

Answer 6

Carried out a series of experiments using cathode rays

Question 7

What did Thompson discover?

Answer 7

The electron

Question 8

How did the cathode rays experiments work?

Answer 8

Cathode rays are emitted from the negative electrode inside cathode ray tubes

Question 9

What specifically did the cathode rays experiment show?

Answer 9

Cathode rays were the stream of particles (electrons) and each particle had the following properties:

1) It had a negative charge
2) It could be deflected by both a magnet and an electric field
3) It had a very small mass

Question 10

What did Thompson conclude?

Answer 10

Cathode rays were actually electrons so must have come from within the atoms of the electrodes themselves

Question 11

What did Thompson propose?

Answer 11

An atom should be thought of as being made up of negative electrons moving around in a sea of positive charge - overall negative charge is the same as the overall positive charge meaning that the atom is neutral with no overall charge

Question 12

What did Thompson create?

Answer 12

The plum pudding model/atom

Question 13

Who brought about the downfall of the plum pudding model?

Answer 13

Rutherford in 1909

Question 14

What did Rutherford do?

Answer 14

Carried out an experiment in which they directed alpha particles towards a sheet of very thin gold foil and measured any deflection of the particles - calculated plum pudding model would hardly deflect any alpha particles at all - they found most were not deflected, only a small % were deflected through large angles with a very few particles being deflected back towards the source

Question 15

What did Rutherford conclude?

Answer 15

An atom’s positive charge must be concentrated into a volume much smaller than the size of an atom

Question 16

What did Rutherford propose?

Answer 16

In 1911, he proposed the nuclear atom:

1) Positive charge and most of its mass is concentrated in the nucleus at the centre
2) Negative electrons orbit this nucleus
3) Most of the atom’s volume would be in the space between the tiny nucleus and the orbiting electrons
4) Overall positive and negative charges must balance

Question 17

What did Bohr do?

Answer 17

In 1913, altered Rutherford’s model to allow electrons to follow only certain paths otherwise electrons would spiral into the nucleus and this was called the planetary atom in which the electrons orbit a central nuclear sun in shells

Question 18

What did Mosely discover in 1913?

Answer 18

A link between x-ray frequencies and elements’’ atomic numbers but he could not explain this

Question 19

What did Rutherford discover in 1918?

Answer 19

The proton and we now know that the atomic number tells us the number of protons in an element atom

Question 20

Outline the order of the discovery of atom

Answer 20

Democritus
Dalton
Thompson 
Rutherford
Bohr
Mosely 
Rutherford

Question 21

What is relative isotopic mass?

Answer 21

The mass of an atom on an isotope compared with 1/12 of the mass of an atom of carbon-12

Question 22

What is relative atomic mass?

Answer 22

Weighted mean mass of an atom of an element compared with 1/12 of the mass of an atom of carbon-12