1.5 History of atom

Question 1

Def of electron

Answer 1

A tiny particle with a negative charge. Electrons orbit the nucleus of atoms or ions in their shells

Question 2

Def nucleus

Answer 2

The very small and dense central part of an atom that contains protons and neutrons

Question 3

Def proton

Answer 3

A tiny positive particle found inside the nucleus of an atom

Question 4

Def neutron

Answer 4

A dense particle found in the nucleus of an atom. It is electrically neutral, carrying neutral charge

Question 5

Who were the first people to have ideas about particles and atoms?

Answer 5

The Ancient Greeks

Question 6

Who suggested that atoms were like tiny, hard spheres?

Answer 6

John Dalton

Question 7

When did John Dalton put forward his ideas about atoms?

Answer 7

Early 1800s

Question 8

What did John Dalton believe about atoms?

Answer 8

• That they were like tiny, hard spheres
• That each element had its own atom that differed from others in terms of mass
• That atoms couldn’t be divided or split, they were the building blocks of nature

Question 10

Why are Dalton’s ideas still useful today?

Answer 10

• They help visualise elements, compounds and molecules
• His models are still used to describe the different arrangement and movement of particles in solids, liquids and gases

Question 11

Who discovered the electron and when?

Answer 11

JJ Thomson at the end of the 1800s

Question 12

How many times smaller is an electron compared to the lightest atom?

Answer 12

2000x

Question 13

How did J.J. Thomson discover the electron?

Answer 13

He dis experiments on the beams of particles. They were attracted to a positive charge, showing that they must be negatively charged themselves

Question 14

What model of the atom did J.J. Thomson propose?

Answer 14

• The plum pudding model
• He said that the tiny negatively charged electrons must be embedded in a cloud of charge
• He knew that atoms themselves carry no overall charge, so any charges in an atom must balance out

Question 15

Who found evidence for the nucleus and when?

Answer 15

Ernest Rutherford and his students Geiger and Marsden, in 1909

Question 16

What experiments were Geiger and Marsden doing and why did it prove the plum pudding model wrong?

Answer 16

• They fired positively charged alpha particles at an extremely thin sheet of gold
• According to the plum pudding model, the particles should have passed straight through the sheet or be slightly deflected at most
• However, some were deflected more than expected or even backwards
• This meant the plum pudding model was wrong

Question 17

Why was Thomson’s model disproved?

Answer 17

• Because positive charge must have been concentrated in a tiny spot in the centre of the atom
• Otherwise the large, positive particles fired at the foil could never be repelled back towards their source

Question 18

What model of the atom was proposed after Geiger, Marsden and Rutherford’s discovery?

Answer 18

It was proposed that the electron must be orbiting around the nucleus, which contains very dense positively charged protons

Question 19

What did Neils Bohr discover?

Answer 19

Niels Bohr revised the atomic model again and suggested that electrons must be orbiting the nucleus at set distances (shells)

Question 20

When were neutrons discovered and by who?

Answer 20

1932 by James Chadwick