chapter 1 the atom -...

Copyright © Pearson Australia 2012 (a division of Pearson Australia Group Pty Ltd) ISBN 978 1 4425 2361 6

Chapter 1 The atom

Unit 1.1

1 proton, neutron, electron

2 Rutherford’s discovery was that the atom contained a small positive

nucleus surrounded by a cloud of electrons. He also found that atoms are

mostly empty space.

3 1st shell – 2, 2nd shell – 8, 3rd shell – 18

4 Electrostatic force

5 a Nuclear model

b Planetary model

c Dynamide model

d Plum pudding model

6 Isotopes are atoms with the same number of protons but a different

number of neutrons. Or: isotopes are atoms with the same atomic number

but different mass number.

7 The atomic number is the number of protons in the nucleus. The mass

number is the total number of protons and neutrons.

8 a The electrons are moving rapidly and randomly, and their location

cannot be specified.

b The electrons are trapped inside the electron shells.

9 Atoms are charge neutral because there is an equal number of electrons

and protons to balance their positive and negative charges.

10 Rutherford fired a beam of positively charged alpha particles at a piece of

thin gold foil and detected the alpha particles after they hit the foil. He

found that most of the alpha particles went straight through, while a few


bounced back. He concluded that atoms were mostly empty space with a

small positively charged nucleus at the centre.

11 The atomic number tells you how many protons are in the nucleus. It

therefore also tells you how many electrons surround the atom.

12 A and D

13 126 C 13

6 C 146 C

14 2,8,2

15 Elements are substances made up of just one type of atom. Compounds

are made up of more than one type of atom.

16 a 2 protons, 2 neutrons, 2 electrons

b 8 protons, 8 neutrons, 8 electrons

c 14 protons, 14 neutrons, 14 electrons

d 82 protons, 125 neutrons, 82 electrons

e 92 protons, 146 neutrons, 92 electrons

17 Atoms are like Lego in that many small pieces can be put together to

create larger and more complicated structures (substances). In addition,

with a relatively few types of atoms or Lego pieces, billions of different

things can be created.

18 Atomic symbols help communicate the exact structure of an atom

efficiently and accurately.

19

20 Creative research task


Unit 1.2

1 Check tables 8.2.1 and 8.2.2 in the chapter (see below)

2 Hydrogen: H+

3 -ide

4 Ionic compounds form crystal lattices.

5 Solubility

6 a potassium ion

b bromide ion

c sulfide ion


7 A cation is an atom that has lost electrons to become a positively charged

ion. An anion is an atom that has gained electrons to become a negatively

charged ion.

8 a When the atom can lose different numbers of electrons.

b For example, iron atoms can lose two or three electrons, forming the

iron(II) ion, Fe2+ or the iron(III) ion, Fe3+.

9 The ions in the crystal lattice are surrounded by water molecules and

dispersed evenly throughout the liquid.

10 Once dissolved, the ions are free to move and so can carry electrical

charge between the electrodes.

11 Responses may include rust (iron oxide), lime scale (calcium oxide)

and table salt (sodium chloride).

12 a A chlorine atom gained an electron.

b A sodium atom lost an electron.

c An oxygen atom gained 2 electrons.

d A calcium atom lost 2 electrons.

e An aluminium atom lost 3 electrons.

13 a sodium chloride, NaCl

b magnesium oxide, MgO

c aluminium fluoride, AlFl3

d copper(II) bromide, CuBr2

e iron(III) oxide, Fe2O3

14 Atoms are charge neutral. Ions have a positive or negative charge.

15 a iron(II) ion and iron(III) ion

b chromium(IV) ion and chromium(V) ion

16 a i X

ii Y

b X2Y3


17 a The liquid will conduct electricity.

b This is because when the crystal becomes a liquid, the ions are free to

move, and so can carry electrical charge between the electrodes in the

same way as when the crystal is dissolved.

18

19 a b c

Na+ F– O2–

Unit 1.3

1 alpha radiation, beta radiation, gamma radiation

2 sieverts

3 1 Sv

4 a The atomic number decreases by 2 and the mass number decreases

by 4.

b The atomic number increases by 1 and the mass number stays the

same.

5 Radiotherapy, radioimaging, sterilisation, measuring the thickness of

metals

6 X-rays, UV rays, visible light, infrared, microwaves, radiowaves


7 A radioisotope is an isotope of an atom that may undergo a nuclear

reaction spontaneously.

8 During fission, a single large nucleus splits into small nuclei. During fusion,

small nuclei come together and fuse into a single nucleus. In both cases,

large amounts of energy are produced.

9 All these forms of radiation have enough energy to knock off electrons

from atoms and molecules.

10 Although alpha particles are very efficient at knocking off electrons, they

have very poor penetration and so will be stopped by layers of dead skin

or just a few centimetres of air.

11 Half-life is the time it takes for half the nuclei of a radioactive isotope to

undergo a nuclear reaction.

12 Radiation burns and sickness are caused when large doses of ionising

radiation ionise molecules in cells, causing the cells to die or perform

inefficiently.

13 168 O 17

8 O 188 O

14 Stable nuclei never undergo nuclear reactions; unstable nuclei may

undergo a nuclear reaction spontaneously at any time.

15 Alpha particles are large, heavy and slow. As a result they have low

penetration but are good at ionising atoms and molecules. Beta particles

are small, light and fast, and so they can penetrate flesh and bones but

will be stopped by a sheet of aluminium. They can also ionise atoms and

molecules but not as well as alpha particles can. Gamma rays are a form

of electromagnetic radiation, so they have no mass or size and travel at

the speed of light. Gamma rays are only stopped by thick lead or concrete.

They have the same ionisation efficiency as beta particles.

16 a atomic number = 93,

mass number = 237

b atomic number = 92,

mass number = 236


c atomic number = 82,

mass number = 206


mass number = 22


mass number = 14


mass number = 137

18 a 5730 years

b 11 460 years

c 17 190 years

d 22 920 years

19 Tabulated answer (see below)

20 Alpha particles have poor penetration, so they could not be detected

inside the body. In addition, they can ionise molecules in the cells, causing

serious damage to the internal organs.

21 Design task

22 Creative writing task


Chapter review

1 a The smallest building block of matter

b A particle made up of a cluster of atoms

c A grid-like structure of atoms

d Atoms that have the same number of protons but a different number of

neutrons.

e An atom that has lost or gained electrons

2 Proton (positive), electron (negative), neutron (neutral)

3 The atomic number is the number of protons in the nucleus. The mass

number is the number of protons plus neutrons.

4 a It must lose electrons.

b It must gain electrons.

5 Alpha, beta and gamma

6 Radiotherapy, radio imaging, sterilisation of food and utensils, measuring

the thickness of metals.

7 Atoms have a small, positively charged nucleus made up of protons and

neutrons that sits at the centre of a large electron cloud.

8 Rutherford fired a beam of positively charged alpha particles at a piece of

thin gold foil and detected the alpha particles after they hit the foil. He

found that while most of the alpha particles went straight through, a few

bounced back. He concluded that atoms were made up of mostly empty

space with a small positively charged nucleus at the centre.

9 Cations and anions are attracted to each other through electrostatic force.

Each cation can attract several anions from all directions. The anions then

attract more cations and so on, forming a large grid-like structure.

10 The ions are surrounded by water molecules, thus restricting attractive

forces between anions and cations, and allowing them to be dispersed

thinly and evenly throughout the liquid.


11 Gamma radiation can penetrate through lead and concrete, while alpha

particles can be blocked by paper or even a layer of dead skin.

12 a Radiation burns and sickness are caused when radiation ionises

molecules in the cells of the skin or organs, resulting in the death of

the cell.

b Mutations are caused when ionising radiation causes a change to the

DNA of the cell, changing the ‘genetic code’. The cell continues to function

and reproduce but not in the way it was intended.

13 a potassium chloride, KCl

b calcium oxide, CaO

c boron fluoride, BF3

d zinc bromide, ZnBr2

e chromium (III) oxide, Cr2O3

14 a 128

b 64

c 32

d 16


mass number = 234


mass number = 14


mass number = 237

d atomic number = 12,

mass number = 22

16 Fusion offers the potential for a power source that is not only unlimited but

also produces very little waste or pollution.


17 Some smoke detectors contain the radioisotope americium-241. This is an

alpha particle emitter, so if breathed in, it could cause damage to the cells

inside your lungs.

18 Diagrammatic answer (see below)

19 Diagrammatic answer (see below).

Thinking scientifically

Q1 C

Q2 D

Q3 A

Q4 C

Q5 C

Q6 C

chapter 1 the atom -...

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