P7

Question 1

rutherford experiment:

Answer 1

narrow beam of alpha particles directed at a thin metal foil.

• most particles went straight through the foil.
• some were deflected through large angles.
• 1 out of 8000 were reflected straight back.

conclusion:
-an atom was made up of a small, positively charged nucleus surrounded by electrons orbiting in a ‘cloud’

Question 2

alpha radiation:

Answer 2

• travels a few centimetres
• can be stopped by paper (least penetrating)
• most ionisation power
• consists of particles (two protons and two neutrons)

Question 3

ionisation:

Answer 3

• alpha, beta and gamma radiation ionise substances they pass through.
• ionisation in a living cell can damage or kill the cell

Question 4

radioactive substance:

Answer 4

• has an unstable nucleus

- unstable nucleus become more stable by emitting alpha, beta or gamma radiation

Question 5

beta decay:

Answer 5

• atomic number goes up by 1( bottom number)

- mass number is unchanged

Question 6

isotope:

Answer 6

• atom with same number of protons but different number of neutrons
• have same atomic number but different mass number

Question 7

gamma radiation

Answer 7

• travels many metres
• can be stopped by thick lead or metres of concrete
• small levels can penetrate air, paper or thin metal
• least ionisation power
• consists of electromagnetic radiation

Question 8

activity:

Answer 8

activity:

• number of unstable atoms that decay per second
• measured in Becquerel (Bq)

Question 9

plum pudding model:

Answer 9

atoms were:
-spheres or positive charge
-with negative charges spread through it
this was incorrect because it couldn’t explain why some Alpha particles were scattered through large angles.

Question 10

gamma decay:

Answer 10

-emissions do not change number of proton or neutrons

Question 11

count rate:

Answer 11

• number of counts per second

- count rate decreases as activity of the source decreases

Question 12

half-life

Answer 12

• average time it takes for number of nuclei of the isotope to halve
• average time it takes for the count rate from the isotope to half its value

Question 13

beta radiation:

Answer 13

• travels tens of centimetres
• can be stopped by thin sheet of aluminium
• can penetrate air and paper
• middle ionisation power
• consists of fast-moving electrons emitted from nucleus

Question 14

alpha decay:

Answer 14

• nucleus loses 2 protons and 2 neutrons
• atomic number (bottom number) goes down by 2.
• mass number (top number) goes down by 4.

Question 15

radioactive decay:

Answer 15

• unpredictable

- occurs if nucleus of an atom is unstable

Question 16

bohr’s model

Answer 16

• electrons absorb electromagnetic (EM) radiation to move away from the nucleus
• electrons emit electromagnetic (EM) radiation to move closer to the nucleus
• his model showed that electrons in an orbit can move to another orbit