Answers To Composition Of Atoms: The Sub-Atomic Particles (Page 3 of 4) in pdf

Answers to Nuclear Chemistry: Radioisotopes and Types of Nuclear Radiation

Homework: Questions 9, 10, 12 and 13 on page 32 of your text.

Read pages 34 and 35. Answer Q 20, 21 and 22 on page 35.

Questions from page 32 of your text:

9. Distinguish between an isotope and a radioisotope.

•

Isotopes are atoms of an element that have different numbers of neutrons. They may or may not be

radioisotopes.

•

Radioisotopes are atoms have an unstable nucleus because they do not have enough, or have too

many, neutrons in the nucleus. The nucleus of most atoms contain both protons and neutrons.

Protons are positively charged, so they repel each other. Neutrons act like spacers in the nucleus to

separate the protons. The right number of neutrons are needed in between the protons to keep the

nucleus from breaking apart. If an atom is a radioisotope, it has an unstable nucleus that eventually

will break apart to release protons, neutrons and/or energy as it achieves a more stable arrangement.

10. Complete the chart:

Alpha Particle

Beta Particle

a) another name for this

aka a helium nucleus

aka a high speed electron

particle

symbols: α or

symbols: β or e

b) the symbol for this

particle

c) how the nucleus of a

when an alpha particle is emitted,

when a beta particle is emitted, a

radioisotope is altered

the nucleus will lose 2 protons and

neutron is converted to a proton

by emission of this

2 neutrons, so the atomic number

and an electron, so the atomic

particle

will go down by 2 and the mass

number will increase by one and

number will go down by 4

the mass number will stay the

same

d) the penetrating ability of

does not penetrate matter so it can

penetrates somewhat into matter

this type of radiation

be stopped by a piece of paper

so it can be stopped by a piece of

metal 1 – 2 mm thick

12. Radon – 222 has a half-life of 4.0 d. If the initial mass of the sample of this isotope is 6.8 g, calculate

the mass of Rn – 222 after:

a) 8.0 d. This is 2 half-lives, so the 6.8 g is divided in half and then in half again. After 8.0 d there

will be 1.7 g of Rn – 222 remaining.

b) 16.0 d. This is 4 half-lives, so the 6.8 g is divided in half 4 times. After 16.0 d there are 0.425 g of

Rn –222 remaining (the answer in the text is wrong).

c) 32.0 d. This is 8 half-lives, so the 6.8 g is divided half 8 times. After 32.0 d there are 0.02656 g of

Rn – 222 remaining (which would round to 0.027 g).

Radioactive Decay of I - 131

13. Graph of radioactive decay of I – 131:

1.75

1.5

Each half life if 8.0 days, so you could

1.25

also put “Time (d)” on the x – axis and go

from 0 to 64 days. The graph will have

0.75

0.5

the same shape.

0.25

Number of Half-lives

Answers To Composition Of Atoms: The Sub-Atomic Particles Page 3

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