Chapter 2 - The Atom

Question 1

Matter

Answer 1

Scientific name for materials

Question 2

The particulate nature of matter

Answer 2

The concept that all matter is made up of small particles

Question 3

NH₃

Answer 3

ammonia

Question 4

HCl

Answer 4

Hydrochloric acid

Question 5

NH₄Cl

Answer 5

Ammonium chloride

Question 6

Diffusion

Answer 6

Spreading of gases

Question 7

What did Greek philosophers say about the atom?

Answer 7

• Matter is made of small particles
• Atoms are indivisible
• Only theory no experiments

Question 8

What was Dalton’s Atomic Theory?

Answer 8

i) Matter is made of small particles called atoms
ii) Atoms are indivisible
iii) Atoms can neither be created nor destroyed

Question 9

What did William Crookes do?

Answer 9

Passed electricity through a nearly vacuumed glass tube → noticed it was luminescent

Question 10

What did William Crookes conclude from his experiments on Cathode rays?

Answer 10

• Cathode Rays travel in straight lines
• They cause glass to fluoresce
• Possess enough energy to move a paddle wheel

Question 11

Who discovered whether electrons were positive or negative?

Answer 11

JJ. Thompson → negative

Question 12

Who proposed the name ‘electron’?

Answer 12

George Stoney

Question 13

What is the ratio of the charge of an electron to its mass?

Answer 13

charge of the electron
——————————– = 1.76 x 10¹¹ coulombs per kg
mass of the electron

Question 14

Coulombs

Answer 14

Units in which quantity of charge is measured

Question 15

Cathode rays

Answer 15

Streams of negatively charged particles called electrons. They travel in straight lines from the cathode to the anode, are deflected by electric and magnetic fields, and have sufficient energy to move a small object such as a paddle wheel.

Question 16

What is the charge of an electron?

Answer 16

1.6 X 10⁻¹⁹ coulomb

Question 17

What is the mass of an electron?

Answer 17

9.1 x 10⁻³¹ kg

Question 18

Who proposed the plum pudding theory and when?

Answer 18

JJ Thompson in 1898

Question 19

Describe the Plum Pudding Model of the atom

Answer 19

The atom was like a sphere of positive charge and electrons are embedded in the sphere at random

Question 20

Who discovered the nucleus of an atom and when?

Answer 20

Ernest Rutherford in 1909

Question 21

How was the nucleus of an atom discovered?

Answer 21

i) alpha particles passed through gold foil
ii) alpha particles are positively charged and have two neutrons and two protons
iii) it was found that some of the particles deflected at large angles when passed through the foil and some were deflected straight back
iv) concluded the atom was mostly made of space with a concentrated area of positive charge at the centre

Question 22

Why, in Rutherford’s experiment, are some of the particles deflected straight back?

Answer 22

Positive alpha particles and the positive nucleus of the atom repelled each other

Question 23

Who discovered the proton and when?

Answer 23

Ernest Rutherford in 1911

Question 24

How were protons discovered?

Answer 24

It was found when lighter atoms such as oxygen or nitrogen were bombarded with alpha particles, positively charged particles were given out. This didn’t happen with the heavier atoms as their larger nucleus repels the alpha particles. The alpha particles broke up in nuclei of the lighter atoms releasing positively charged particles called protons

Question 25

Who discovered the neutron and when?

Answer 25

James Chadwick in 1932

Question 26

How was the neutron discovered?

Answer 26

Beryllium was bombarded with alpha particles. It was discovered that type of radiation consisting of neutral particle came from the beryllium. These particles have the same mass of a proton and they were called neutrons