Chapter 5 Chemical Bonding

Chapter 5 Chemical Bonding Stability of noble gases (group 18) 1. All the noble gas atoms have 8 electrons in their valence shells which known as octet electron arrangement except helium atom 2. Helium atom has only one shell filled with two electrons and it is very stable. This extremely stable electron arrangement is known as the duplet electron arrangement. 3. The noble gases are the most stable electron arrangements, as the result, atoms of noble gases do not lose, accept and share electrons with other atoms. 4. Noble gases are chemically unreactive and exist as monoatomic gases. Ionic bonding 1. Formed between atom of  metal and atom of  non-metal to produce a compound 2. Formed through the transfer of electrons from the metal atoms to the non-metal atoms 3. Metal atoms from Group 1, 2 and 13 will release their valence electrons to achieve the stable octet electron arrangement. A positive ion (cation) is formed. Formation of cations An atom that loses electrons from the valence shell forms a positive ion called cation The cation has more protons than electrons Metals form positive ions 

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4. Non-metal atoms from Group 15, 16 and 17 will accept electrons to achieve the stable octet electron arrangement. A negative ion (anion) is formed. Formation of anions An atom that accepts electrons into valence shell forms a negative ion called anion The anion has more electrons than protons Non-metals form negative ions 

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5. The positive ions and negative ions are attracted to each other by strong electrostatic force of attraction in ionic bonds. b+ a6. For an ionic compound that consists of  cations, M and anions, X , the formula of the ionic compound formed between them is written as MaXb. Covalent bonding 1. Formed between atoms of  non-metals combine with each other to form a molecule. 2. Formation of covalent bond, atoms of non-metal share electrons to achieve the stable octet electron arrangement. 3. Non-metal involved: Group 15, 16, 17, carbon and silicon from Group 14, hydrogen atom. 4. There are three types of covalent bonds: i. Single bond: sharing one pair of electron ( gas chlorine molecule, Cl 2) Double bond: sharing two pairs of electron (gas oxygen molecule, O 2) ii. Triple bond: sharing three pairs of electron (gas nitrogen molecule, N 2) iii.

The differences in physical properties between ionic compounds and covalent compounds Ionic compounds Have high melting and boiling points Exists as solids at room temperature, non-volatile Conduct electricity in the molten state or aqueous solution but do not conduct electricity in the solid state Usually soluble in water but insoluble in organic solvents such as ether, alcohol

Covalent compounds Have low melting and boiling points Usually exits as volatile liquids or gases at room temperature Do not conduct electricity in the solid and liquid states

Usually insoluble in water but soluble in organic solvents

Types of covalent molecules a) Simple molecules  –  water, carbon dioxide b) Macromolecules (giant molecules)  –  silicon dioxide and diamond

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All atom are bonded to each other by covalent bonds in a giant lattice structure Have the high melting and boiling point because a lot of heat energy is needed to break the strong covalent bonds in the giant lattice structure Cannot conduct electricity because they do not have free mobile ions Are insoluble in water

Uses of covalent compounds as solvents Solvents Turpentine Petrol and kerosene Alcohols Alcohols and ethers Propanone Alcohols. Ethers and propanone

Uses

To dissolve paint To remove greasy or oily dirt In medicine such as iodine solution Solvents for ink and dyes To remove nail varnish Preparation of cosmetic products  –  perfumes

Exercise: 1. Table 1 shows three elements represented by the letters P, Q and R with their respective electron arrangement. Element Electron arrangement P 2.8.8 Q 2.8.1 R 2.8.7

a) i) Which element is probably a noble gas? _____________________________________________________________ ii) Explain why the noble gas is very stable. _____________________________________________________________ b) State the type of chemical bond in molecule R. __________________________________________________________________ c) R reacts with Q to form a compound. i ) State the type of chemical bond in this compound. _______________________________________________________________ ii ) Draw a diagram to show the electron arrangement in this compound

iii) State one property of the compound formed when the two elements react chemically. _______________________________________________________________________