chapter 4: chemical patterns answers - st leonard's · pdf filechapter 4: chemical...

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Chapter 4: Chemical patterns

Answers

Think about chemical patterns

Who was Dmitri

Mendeleev and how was

he able to predict the

future?

Dmitri Mendeleev was a Russian chemist who produced a

periodic table of elements in the late nineteenth century. The table

ordered the elements in rows and columns, according to

increasing atomic weight. He left spaces for undiscovered

elements and, from their positions in the table, he could predict

their properties.

What are metalloids? Metalloids (or more commonly semi-metals) are elements that

have some properties similar to metals and some similar to non-

metals.

Why is the petrol used for

most vehicles unleaded?

Leaded petrol was replaced by unleaded petrol so that lead in the

exhaust did not contaminate the environment.

Why do we talk about

shells when describing

electrons?

The electron shells are energy levels that radiate outwards.

Electrons occupy these shells. The lowest energy level or K shell

is closest to the nucleus. Higher energy shells form concentric

layers with greater radii.

Why are you more likely

to find pure gold on or

near the Earth’s surface

than pure copper or iron?

Copper and iron are more reactive than gold. Copper and iron will

react with other elements to form compounds. Gold is quite

unreactive and rarely reacts with other elements.

What is the connection

between the reactivity of

metals and the ancient

Roman Empire?

In ancient Rome, ores were imported and smelted to produce

metals. The less reactive the metal, the easier it was to smelt the

ore to produce the metal. The ores of reactive metals could not be

smelted because the amount of energy required was too great. The

metals that were produced (such as gold, silver, copper, lead) had

a variety of uses, including coinage , jewellery and tool.

How is it possible to write

‘aluminium nitrate’ using

only four letters?

Using chemical symbols, the formula is Al(NO3)3, thus four

letters — A. l , N and O — are used.



Your quest

1. (a) Electron

(b) Neutrons and protons

(c) Charged = protons and electrons; uncharged = neutrons

(d) Protons

(e) Electrons

(f) Electrons

2. (a) Carbon

(b) Protons

(c) Carbon

3. Positive

4. Individual student research.

5. (a) Hydrogen and oxygen

(b) Silicon

(c) Sodium

(d) Sodium and chlorine

(e) Mercury

Understanding and inquiring

4.1 Patterns, order and organisation: The periodic table

1. (a) True

(b) True

(c) True

(d) True

2. (a) Magnesium

(b) Fluorine

(c) Potassium

(d) Argon

3. The diagram should show the following.

Noble gases — group 18

Alkali metals — group 1

Alkaline earth metals — group 2

Halogens — group 17



Transition metals — between groups 2 and 13

4. (a) A, D, I

(b) B, E, G, H, J

(c) H, J

(d) A, I

(e) Group 1: B, E; Group 16: D, F, K; Group 18: A, I

(f) Second period: B, C, D, A; Third period: G, F; Fourth period: H, K, I; Sixth

period: E, L

(g) B, E

(h) L

5. The mass number is the total number of protons and neutrons in the nucleus of an

atom. However, many elements exist as isotopes; that is, their atoms may contain a

different number of neutrons. Therefore, an average, or weighted mean, is calculated

to take this into account.The weighted mean is called the relative atomic mass.

6. As you go across the periodic table from left to right, the metallic character of the

elements decreases. Non-metals are found on the upper right-hand side of the table.

7.

8 In the periodic table, the elements are in groups that have similar chemical properties.

This shows the periodicity, or repeating pattern, of the elements’ chemical properties.

Using the table, it is possible to make accurate predictions about the properties of

elements in the same group.

9. Noble gases (group 18)

10. to 15. Responses will vary.

16. to 17. eBookPLUS activity



4.2 Small but important

1. Shells

2. (a) 2

(b) 8

(c) 18

(d) 32

3. The last shell that contains 1 to 8 electrons; it is called the valence shell

4. The group number of an electron can be used to determine the number of outer shell

electrons.

Group 1: 1 outer shell electron

Group 2: 2 outer shell electrons

Groups 3–12: these elements have variable valencies; commonly, these elements have

1,2,3 or 4 electrons in their valence shell

Group 13–18: outer shell electrons = group number 10

eg. group 14 has 14–10 = 4 outer shell electrons; group 17 has 17–10 = 7 outer shell

electrons

5. The period number tells us the number of electron shells around the nucleus.

6. (a) Carbon

(b) Helium

(c) Phosphorus

(d) Calcium

7. (a) 2, 3

(b) 2, 8

(c) 2, 8, 8, 1

(d) 2, 7

(e) 2, 8, 4

8. (a) Metal. Elements with 1, 2 or 3 outershell electrons prefer to lose electrons to

achieve a stable electronic shell arrangement.

(b) Non-metal. Elements with 5, 6 or 7 electrons in the outershell prefer to gain

electrons to achieve a stable electron shell arrangement.

(c) Eight electrons in the outer shell is very stable. These are the noble gases and

they are the most unreactive elements in the Periodic table.



9. The colours of various flames containing metal ions is evidence of the existence of

electron shells. When a metal ion is heated in a flame, electrons can be promoted up

into a higher, unfilled energy level, and they then fall back to a more stable shell and

emit light of a characteristic wavelength. Different colours are associated with

differing amounts of energy released as the electron moves from a higher to a lower

shell.

10. Student's own research

11. Student's own work

12. eBookPLUS activity

4.3 When atoms meet

1. Ions form when atoms gain or lose electrons in order to achieve a full outer shell of

electrons, which is a very stable arrangement.

2. A positively charged ion is called a cation.

3. A negatively charged ion is called an anion.

4. Most ionic compounds are solid at room temperature; they have high melting points;

they usually dissolve in water to form aqueous solutions, and these solutions usually

conduct electricity.

5. Metal and non-metal elements combine to form ionic compounds.

6. (a) Na+

(b) N3−

(c) K+

(d) F−

7. (a) 4 electrons lost

(b) 1 electron gained

(c) 3 electrons lost

(d) 2 electrons gained



8. (a)

(b)

(c)

(d)

9. Individual student response

10. eBookPLUS activity

4.4 When sharing works best

1. Non-metal elements combine to form covalent compounds.

2. A covalent bond occurs when two atoms share their outer shell electrons.



3. An electron dot diagram represents the symbol for the atom and the arrangement of

the outer shell electrons.

4. Most covalent compounds exist as gases, liquids or solids with low melting points.

They do not usually conduct electricity and are usually insoluble in water.

5. In a single covalent bond, two electrons are involved. In a triple covalent bond, six

electrons are involved.

6. (a) Double bonds

(b) Single bonds

(c) One triple bond, two single bonds

7.

8 The noble gases do not form covalent bonds because their outer shells are complete,

each with eight electrons. There is no need to share electrons with other atoms to

achieve a stable outer shell.

9 Oxygen and carbon dioxide are both molecules because, in both cases, atoms are held

together as a unit by the sharing of electrons.

10. Individual research

11. Individual research

12 eBookPLUS activity

4.5 How reactive?

1. Hydrogen

2. Iron is a reactive metal that combines with oxygen and water to form a variety of iron

3. The active metals of the periodic table are on the left. They readily lose their valence

or outer-shell electrons to form a stable octet. As you move across the table, the



elements become less metallic and more non-metallic. Non metals prefer to gain

electrons than lose them. Metals, such as sodium and potassium, have one valence

electron, which is readily lost. Therefore, they are very reactive.

4. Individual experiment. Students will repeat investigation 4.4 or 4.5 using the alloys

provided.

5. Individual student research

6. Individual student research

4.6 Finding the right formula

1 A chemical formula is a shorthand way of writing the name of a compound or

molecular element.

2 The molecular formula is a way of describing the number and type of atoms that join

to form a molecule.

3 The formula of a compound tells us the number and type of atoms that it consists of.

4 Na, H, K, Pb, Cl, I, S

5 (a) Hydrogen, nitrogen and oxygen

(b) Sodium, hydrogen, carbon and oxygen

(c) Iron and sulfur

6 The valency of an element is equal to the number of electrons that each atom would

need to gain, lose or share in order to fill its outer shell.

7 (a) 2

(b) 3

(c) 1

8 Sodium = 1; hydrogen = 1; lead = 2; chlorine = 1; iodine = 1; magnesium = 2;

sulfur = 2

9 NaCl — sodium chloride; Al2 (SO4 )3 — aluminium sulfate;

NaOH — sodium hydroxide; AlCl3 — aluminium chloride;

Na3N — sodium nitride; Al(OH)3 — aluminium hydroxide;

Na2O — sodium oxide; AlN — aluminium nitride;

Na2SO4 — sodium sulfate; Al2O3 — aluminium oxide;

CuO — copper (II) oxide; Li3N — lithium nitride;

Cu(OH)2 — copper (II) hydroxide; LiCl — lithium chloride;

Cu3N2 — copper (II) nitride; LiOH — lithium hydroxide;

CuSO4 — copper (II) sulfate; Li2O — lithium oxide;



CuCl2 — copper (II) chloride; Li2SO4 — lithium sulfate;

Fe(OH)3 — iron (III) hydroxide; FeCl3 — iron (III) chloride;

FeN — iron (III) nitride; Fe2O3 — iron (III) oxide; Fe2(SO4)3 — iron (III) sulfate

10 Chlorine and sodium both have a valency of 1. The electrovalency of chlorine is −1

and the electrovalency of sodium is +1. Electrovalency is different to valency because

it takes the charge of the ion into account.

11 (a) O2

(b) Cl2

(c) Pb

(d) NO

(e) ZnO

(f) K2SO4

(g) Ca(OH)2

12 (a) Ammonium chloride

(b) Potassium iodide

(c) Aluminium nitrate

(d) Iron hydroxide

(e) Potassium hydrogen carbonate

(f) Magnesium carbonate

(g) Hydrogen nitrate (nitric acid)

13 Group 18 is not listed because these elements do not require any electrons to fill their

outer shell. They are already complete; therefore, they have a valency of zero.

14. Individual and group discussion

15. Individual work or group work.

16 eBookPLUS activity



4.7 Concepts and Mind Maps

1 (a)

(b) Student's own work. The following is an example.



2. (a)/(b) Student work. The following is a simple concept map.

3. The following is one possible response; students may elect to relate the three concepts to

positions in the periodic table.



4.

One possible response:



Looking back

1. The elements belong to families or groups. By arranging them in the form of a

periodic table, the family relationship can be seen. Each member of a family has the

same number of valence electrons and similar chemical properties. No knowledge of

the relationship is gained by arranging the elements in a simple table.

2. The group number tells us how to determine the number of outer shell electrons in an

atom of that element. For groups 1 and 2, the number of outer shell electrons is 1 and

2 respectively. For Groups 13 to 18, the number of outer shell electrons is the group

number minus 10. The period number tells us how many electron shell are present.

Thus, period 3 contains elements that have 3 shells of electrons.

3. The properties of elements show gradations as one moves down a group and across a

period. When Mendeleev produced a periodic table, the element germanium was not

known and so he left a space in his table. By using the known properties of

surrounding elements, he was able to accurately predict the properties of the missing

element. This assisted scientists to discover the element.

4. Water is a compound and not an element.

5. (a) Z = 14, A = 28, p = 14, n = 14, e = 14

(b) Z = 24, A = 52, p = 24 n = 28, e = 2 4

(c) Z = 79, A = 197, p = 79, n = 118, e = 79

(d) Z = 82, A = 206, p = 82, n = 124, e = 82

(e) Z = 94, A = 242, p = 94, n = 148, e = 94

6. 18 (noble gases)

7. Shiny, malleable, ductile, good heat conductor, good electrical conductor

8. Dull, brittle, heat insulator, electrical insulator, low melting points

9. (a) More reactive

(b) Less reactive

10. (a) Increases

(b) Increases

(c) Decreases

(d) Decreases

11. Metalloids have properties that are often in between those of metals and non-metals.

Silicon, for example, is shiny like a metal but is only a semi-conductor of electricity.



12.

13. Note: This question has errors and needs correction as shown:

Answers to revised question:

(a) 12

(b) 24

(c) 12

(d) Some have a different neutron number (i.e. they are isotopes of magnesium)



14.

15. (a) Neon

(b) Mg2+

or Al3+

(c) F− or O

2−

16. (a) Li atoms lose one electron and F atoms gain one electron. The lithium ion and

the fluoride ion form lithium fluoride

(b) Na atoms lose one electron each to form sodium ions. Oxygen atoms gain two

electrons to form the oxide ion. Two sodium ions and one oxide ion forms

sodium oxide.

17. (a) Hydrogen atoms and chlorine atoms each donate one outer shell electron to

form a shared pair or covalent bond. This results in the formation of hydrogen

chloride

(b) Nitrogen atoms have three outer shell electrons and hydrogen atoms have one

outer shell electron. Three covalent bonds are formed when electrons from

each atom are shared to form three shared pairs.

18. Ionic compounds are composed of oppositely charged ions. In the solid state the ionic

compounds do not conduct, but when melted or dissolved in water they do electrically

conduct. Ionic compounds generally have high melting points. Covalent compounds

are made up of neutral atoms bonded together by covalent bonds. They do not

conduct in the solid, melted or dissolved states. Covalent compounds have low

melting points.



19. Gold is a very stable metal and quite unreactive. It is less likely to react with other

materials in the environment compared with copper. Over long periods of geological

time, most copper has formed compounds but gold is present today as the pure

element.

20. Potassium, sodium and calcium are very reactive elements and combine with air or

water to form compounds. No samples of these metals exist in the crust today. On the

other hand, metals like gold, silver and copper are far less reactive and so some ore

bodies are present today which contain the pure metal.

21. (a) O2

(b) CO2

(c) Al2O3

(d) NaF

(e) CaCO3

(f) ZnCl2

(g) Fe2S3

(h) SO2

(i) C

(j) Pb

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