1-5 Bonding In Compounds (part 7)

V.Bonding in compounds

Topic

V.

Part 7

Bonding in compounds

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Part 7

Reference Reading Objectives

1.5.3.0 – predict the formulae of compounds when the group numbers of constituent elements are given

Notes

D. Prediction of formation of ionic and covalent compound Formation of different compound Metal / non-metal system:

Non-metal / non-metal system:

Metal / metal:

Glossary

alloy

Ionic bond is formed when one kind of atoms has extra electrons and another kind of atoms has insufficient number of electron. (e.g. sodium and chlorine or metal / non-metal system). The electrons are transferred from the former one to the latter one. The ions formed are held together by electrostatic attraction.

Covalent bond is formed when both atoms do not have enough electrons. (e.g. hydrogen and chorine or non-metal / non-metal system). The two atoms share their electrons to attain completely filled outermost shell. The electrostatic attraction between nucleus-shared electrons-nucleus holds the atoms together.

When two metals come together, they do not form compound at all. They only form a mixture called alloy. An alloy does not have a fixed composition e.g. different steels are comprised of different amount of iron, carbon, chromium and nickel. Therefore, alloy is not a compound. The force sticking the metal atoms together is called metallic bond. The details of alloy and metallic bond will be discussed in the topic of metal.

V.Bonding in compounds

Past Paper Questions 95 I 4 4

Part 7

95 I 4 99 I 6 a i

"When atoms combine, they tend to attain noble gas electronic structures." Discuss how atoms can attain the noble gas electronic structures. In your answer, you should give suitable examples and the electronic structures of the products formed. Chemical knowledge (5 marks) When atoms of non-metals combine, they tend to share their (valence / outermost) electrons to form molecules. 1 mark Electronic structure of a molecule e.g. HCl / Cl2 etc. (Any appropriate example) 1 mark

When metal and non-metal combine, atoms of the metal donate elections (to atoms of non-metals) to form cations / positive ions / metallic ions, while atoms of the non-metal accept electrons to form anions / negative ions / non-metallic ions. 1+1 marks (or, award 1 mark for electron transfer, 1 mark for the formation of cation and anion) Electronic structure of an ionic compound e.g. NaCl etc. (Any appropriate example) 1 mark

C

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Effective Communication (3 marks) Most candidates just stated that ionic bond is formed by losing and gaining electrons without mentioning the formation of cations and anions. A number of candidates discussed the formation of only one type of bond, either covalent or ionic. Some wrote a long paragraph, but failed to include electronic structures for the products.

99 I 6 a i 6a Water is a compound of hydrogen and oxygen. Under suitable conditions, 80.0 cm3 of hydrogen and 60.0 cm3 of oxygen (with one of the reactants in excess) react to give water. The volumes of both gases are measured at room temperature and pressure. i Draw the electronic diagram of water, showing electrons in the outermost shells only.

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V.Bonding in compounds Part 7 90 3 C 3 The atomic numbers of element X and element Y are 13 and 16 respectively. The formula of the compound formed between X and Y is likely to be A. XY2. B. X2Y. C. X2Y3. D. X3Y2. 91 2 Directions : Questions 1 and 2 refer to the following table. Element W X Y Z Atomic number 4 8 14 20 The formula of the compound formed between X and Z is likely to be A. XZ. B. XZ2. C. X2Z. D. X2Z3.

A

2

C

4

The element with atomic number 11 will combine most readily with the element whose atomic number is A. 12 B. 13 C. 17 D. 18

C

1

If the atomic number of an element X is 13, the formula of its oxide is A. XO2. B. XO3. C. X2O3. D. X3O2.

93 4

94 1

97 30 C

99 39 C

30 M is an element in the third period of the Periodic Table. M forms a sulphate which has the formula M2(SO4)3. The formula of the nitrate of M is A. MNO3. B. M(NO3)2. C. M(NO3)3. D. M2(NO3)3.

39 Element X has an isotope 31 X . Which of the following 15 statements is/are correct ? (1) X belongs to Group V of the Periodic Table. (2) X can react with oxygen to form an ionic compound. (3) A. B. C. D.

31 15

X has 16 neutrons.

(1) only (2) only (1) and (3) only (2) and (3) only

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