History Of The Atom

Question 1

What is a atom

Answer 1

The smallest part of an element which still has the properties of that element

Question 2

What is an Element

Answer 2

substance that cannot be broken down into anything simpler by chemical means

Question 3

Matter

Answer 3

Anything which takes up space and has mass

Question 4

What did the Greek philosophers propose

Answer 4

Matter was composed of small particles, these particles were so small they couldn’t be broken down into smaller particles (indivisible)

Question 5

What did John Dalton develop

Answer 5

John Dalton developed the atomic theory

Question 6

What is the atomic theory

Answer 6

All matter is made up of tiny indivisible particles called atoms that can be neither created nor destroyed. Atoms of the same element have identical atomic mass.

Question 7

Who conducted the first experiments on cathode rays

Answer 7

William crookes

Question 8

What are the properties of cathode rays
From William crooked experiments

Answer 8

Cathode rays travel in straight lines (sharp shadow)
Cathode rays cause glass to fluoresce when they strike it
Cathode rays have enough energy to move a paddle wheel

Question 9

Who discovered electrons

Answer 9

JJ Thomson

Question 10

What did JJ Thompson discover (in relation to the electron)

Answer 10

The charge to mass ratio
Discovered electrons are negatively charged

Question 11

What model did JJ Thomson propose

Answer 11

The plum pudding model

Question 12

Who discovered the exact charge of an electron

Answer 12

Robert Milikan

Question 13

What experiment did Robert Milikan do to determine the exact charge of an electron ?

Answer 13

Oil droplet experiment

Question 14

Who discovered the nucleus

Answer 14

Ernest Rutherford

Question 15

Describe the golf foil experiment

Answer 15

Thin beam of alpha particles from a lead box with a sample of radium
Gold foil that acted as a thin layer of atoms
Detector screen
Very unexpected results

Question 16

What model did Rutherford propose

Answer 16

Nuclear model

Question 17

Who discovered neutrons?

Answer 17

James Chadwick

Question 18

How did James Chadwick discover neutrons

Answer 18

By bombarding a beryllium sample with alpha particles, the neutrons were released at a detector / counter for protons

Question 19

What is the atomic mass of an electron

Answer 19

1/1840

Question 20

What are cathode rays

Answer 20

They are an electrical current coming from the negative end of a power supply

Question 21

What are alpha particles

Answer 21

Positivity charged particles from a radioactive source

Question 22

What was William Crookes investigating in the cathode ray expeirment

Answer 22

Investigate what happens when an electric current is passed through a gas tube containing air at low pressure (vacuum tube)

Question 23

Describe the cathode ray experiment done by crookes

Answer 23

Cathode rays came from the cathode end of a power source. He showed the existence of this radiation

Question 24

What was JJ Thompson investigating in his cathode ray expeirment

Answer 24

Investigated if the cathode rays discovered by crooked consisted of charged particles

Question 25

Describe the cathode ray expeirment done by JJ Thompson

Answer 25

Obtained a narrow beam of cathode rays by passing them through a small hole in the anode.
If there was no charge on the magnetic plates the beam passed in a straight line.
But since the cathode rays were attracted so the positive plate, he concluded they consisted of negatively charged particles

Question 26

Describe Thomsons plum pudding model

Answer 26

An atom is a sphere is positive charge. Electrons are embedded in the sphere at random. No evidence to prove

Question 27

Describe the oil drop experiment by Robert Millikan

Answer 27

Sprayed tiny droplets of oil between two charged metal plates.
Ionised air( molecules in air lost electrons). The oil drops picked up the electrons. The oils droplets became attracted to the positive plate. Adjusted charge until stationary

Question 28

Describe the expected results of the Gold foil by Ernest Rutherford

Answer 28

Based on Thomson’s plum pudding model, he predicted most of the atoms would pass straight through the gold foil. The positive charge would be too weak to affect the electrons

Question 29

Explain the expected results of the gold foil experiment

Answer 29

Based on the plum pudding model by JJ Thompson, he predicted most of the atoms would pass straight through the gold foil. The positive charge would be too weak to affect the electrons

Question 30

Describe the actual results of the gold foil experiment

Answer 30

While most of the alpha particles pass straight through the gold foil, a few alpha particles were deflected more than 90 degrees, and even smaller amount were deflected along the path they came from

Question 31

What conclusion did Ernest Rutherford derive from the results

Answer 31

The positive charge must be localised over a tiny volume of the atom, which contains most of the atoms mass.
Since most of the alpha particles pass straight through , the atoms must be mostly made up of empty space

Question 32

Describe the nuclear model

Answer 32

Positive nucleus with an electron cloud