P1.1 Models Of The Atom

Question 1

Define: atom

Answer 1

the smallest particle of an element, made of protons, neutrons, and electrons

Question 2

Define: Bohr model of the atom

Answer 2

Bohr model is a system consisting of a small, dense nucleus surrounded by orbiting electrons with attraction provided by electrostatic forces.

It explains why electrons in orbit do not spiral in to the centre of an atom

Question 3

Define: electron

Answer 3

Elections are a subatomic particle orbiting the nucleus of an atom.
It has a relative charge of -1, and a very small mass.

Question 4

Define: electron shells

Answer 4

the orbits around an atom that are allowed for electrons in the Bohr model

Question 5

Define: model

Answer 5

A description, analogy, or equation that helps you to explain the physical world.

Scientists discover models of the atom by collecting evidence from practical investigation/experiment.

The models become accepted when the evidence agrees with theory and is then shown to be true by scientists who repeat the investigation and get the same/similar results.

Question 6

Define: neutron

Answer 6

subatomic particle found in the nucleus of an atom. It has no charge and a relative mass of 1

Question 7

Define: nucleus

Answer 7

The nucleus is a small dense mass at the centre of an atom made of protons and neutrons

Question 8

Define: order of magnitude

Answer 8

A number to the nearest power of 10.

An increase of two orders of magnitude is the equivalent of multiplying by 100.

Question 9

Define: plum-pudding model of the atom

Answer 9

The plum-pudding model of the atom is an outdated model of the atom in which electrons are embedded in a sphere of positive charge

Question 10

Define: proton

Answer 10

subatomic particle found in the nucleus of an atom. It has a relative charge of +1 and a relative mass of 1

Question 11

Define: Rutherford model of the atom

Answer 11

A model with a positively charged nucleus and electrons in orbit around it

Question 12

Compare Dalton’s and Thomson’s atomic models

Answer 12

Dalton’s atom was a simple indivisible and indestructible solid sphere. The spheres for one element was different from the spheres for another (but he did not know how).

Whereas J. J. Thompson’s model contained particles that were smaller subatomic particles inside an atom/electrons. J. J. Thomson’s model was made of two components – negative electrons and positive mass.

Question 13

Explain how Rutherford’s observations led him to suggest that an
atom has a nucleus.

Answer 13

In the alpha particle experiment,

The majority of the alpha particles passed through with little or no deflection so the majority of the atom is empty space/vacuum.

A few alpha particles were deflected backwards, showing that there is a small, massive nucleus at the centre.

1 in 8,000 was scattered through large angles so the mass of the atom is very concentrated at the centre of the atom.

This mass (nucleus) is positively charged. This mass (the nucleus) is very small compared to the size of the atom.

There would not be any alpha particles scattered through large angles if the plum pudding model were correct.

Question 14

State the diameter of a typical atom.

Answer 14

1 x 10 ^ -10 m

Question 15

State the typical the radius of a nuclei.

Answer 15

10 ^ -15 m

Question 16

Describe: the observations of Rutherford, Geiger, and Marsden’s experiment.

Answer 16

The majority of the alpha particles passed through with little or no deflection so the majority of the atom is empty space/vacuum.

A few alpha particles were deflected backwards, showing that there is a small, massive nucleus at the centre.

1 in 8,000 was scattered through large angles.

Question 17

Describe the conclusions from Thomson’s experiments with

cathode rays.

Answer 17

Cathode rays were made of particles. The particles had a mass smaller than an atom. The particles were negative. Atoms were neutral.

Question 18

Describe the similarities and differences between the plum pudding model described by J. J. Thomson and the nuclear model described by Ernest Rutherford.

Answer 18

Similarities: both models include positive and negative charges;
both models suggest that atoms are tiny particles; both models
suggest an overall neutral charge.

Differences: The nuclear model of Rutherford suggests that the atom
has a positive nucleus surrounded by orbiting electrons and that
most of the mass of the atom is in the nucleus and that the nucleus
has a positive charge.

Question 19

Describe the similarities and differences between the models of the atoms for the nuclear model described by Ernest Rutherford and the Bohr model of the atom.

Answer 19

Similarities: Rutherford and Bohr models of the atom both have a positive nucleus and electrons that orbit the nucleus.
Difference: Bohr’s atomic model is better than Rutherford’s model. Bohr model has electrons orbiting in shells of well-defined, discrete energy levels.

Question 20

Explain the difference between the Democritus model of the atom and Dalton’s.

Answer 20

There was no scientific equipment to do experiments on atoms. Democritus thought that there were atoms because of a BELIEF he had about the nature of matter. Dalton’s model was a simple solid sphere. The sphere for one element was different from the sphere for another (but he did not know how).

Question 21

Explain how Thompson’s model is incorrect.

Answer 21

In the alpha particle experiment, a few alpha particles were deflected backwards, showing that there is a small, massive nucleus at the centre. There would not be any alpha particles scattered through large angles if the plum pudding model were correct.

If Thomson’s model was correct then the electrons should spiral in until they hit the nucleus, but they do not do this.