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ADDITIONAL SCIENCE FORM 4

CHAPTER 8: CHEMICAL BONDING8.1 STABILITY AND ELECTRON CONFIGURATION Atoms with the duplet or octet valence electron configuration are stable. The most stable atoms are the noble gases in group 18 because they have duplet (helium) or octet (other than helium) valence electron configuration. 8.1 STABILITY AND ELECTRON CONFIGURATION Most other elements in the Periodic Table are reactive because their atoms do not have stable valence electron configuration.

Metal atoms donate their valence electrons to become positive ionsNon-metal atoms receive one or more valence electrons to become negative ions Non-metal atoms share one or more valence electrons to achieve the duplet or octet valence electron configuration

8.2 IONIC BONDTransfer of electronsAn metal atom becomes a positive ion by donating its valence electrons. The positive ion has a stable valence electron configuration. The electrons donated by the metal atom are received by the non-metal atoms. The non-metal atom becomes a negative ion with a stable valence electron configuration. 8.2 IONIC BONDExample 1The electron configuration of a lithium atom is2.1. The lithium atom donates its valence electron to form a lithium ion that has +1 charge. Li Li+ + e-

8.2 IONIC BONDExample 2The electron configuration of a fluorine atomis 2.7. The fluorine atom receives one valenceelectron to form a fluoride ion that has -1 charge. F + e- F-

8.2 IONIC BONDThe charge on an ion is an electrostatic charge. Thus, a positive ion and a negative ion are attracted to each other by an electrostatic force of attraction (ionic bond).An ionic compound is formed from a metal and a non-metal. M + X MX Metal Non-metal Ionic compound8.2 IONIC BONDNa CI Na + CI -Formation of sodium chloride, an ionic compound 8.2 IONIC BOND8.3 COVALENT BONDAtoms of non-metals achieve the stable valence electron configuration by sharing electrons.The electrostatic force of attraction between the shared electrons and the nuclei of both atoms is called covalent bond.

8.3 COVALENT BONDExample 1In a hydrogen molecule, two hydrogen atoms share a pair of electrons to form a single covalent bond. Each hydrogen atom in the molecule achieves the stable duplet electron configuration.

8.3 COVALENT BONDH H H H or H-H

8.3 COVALENT BONDExample 2In a carbon dioxide molecule, the carbon atom share four pairs of electron with two oxygen atoms. The carbon atom has the stable octetvalence electron configuration and each oxygen atom has the stable octet valence electron configuration.

8.3 COVALENT BOND O C O O C O or O=C=O 8.3 COVALENT BOND