Chemical Bonding Review

Valence electrons Electrons in the highest occupied energy level of an atom or ionElectrons in the highest occupied energy level of an atom or ion These electrons determine the properties of the atomThese electrons determine the properties of the atom How do we know how many valence electrons an atom or ion has?How do we know how many valence electrons an atom or ion has? ELECTRON CONFIGURATIONELECTRON CONFIGURATION

Valence Electrons Also related to the group number of the element for atomsAlso related to the group number of the element for atoms Group 1A-1 Valence electronGroup 1A-1 Valence electron Group 2A-2 Valence electronsGroup 2A-2 Valence electrons Group 3A-3 Valence electronsGroup 3A-3 Valence electrons Group 4A-4 Valence electronsGroup 4A-4 Valence electrons Group 5A-5 Valence electronsGroup 5A-5 Valence electrons Group 6A-6 Valence electronsGroup 6A-6 Valence electrons Group 7A-7 Valence electronsGroup 7A-7 Valence electrons Group 8A-8 Valence electronsGroup 8A-8 Valence electrons

Can we draw those? Yes!Yes! Let’s draw the valence electrons forLet’s draw the valence electrons for Mg (I will do the first one)Mg (I will do the first one) K N O F

Lewis Structures Valence electrons are usually the only ones used in chemical bondingValence electrons are usually the only ones used in chemical bonding Therefore, we can represent atoms and ions using ELECTRON DOT or LEWIS NOTATIONTherefore, we can represent atoms and ions using ELECTRON DOT or LEWIS NOTATION

OK, so what? The octet rule helps us decide if an atom will gain or lose an electron, or tell us how many bonding electrons it can share in a chemical bondThe octet rule helps us decide if an atom will gain or lose an electron, or tell us how many bonding electrons it can share in a chemical bond

The Octet Rule Which atoms have the most stable or preferred electron configurations?Which atoms have the most stable or preferred electron configurations? NOBLE GASESNOBLE GASES Apart from He, how may valence electrons do each of the noble gases have?Apart from He, how may valence electrons do each of the noble gases have? 8 What is the electron configuration of these valence electrons?What is the electron configuration of these valence electrons? ns 2 np 6ns 2 np 6

The Octet Rule So, all other atoms want to have this stable configuration with 8 valence electronsSo, all other atoms want to have this stable configuration with 8 valence electrons This is the OCTET RULEThis is the OCTET RULE OCTET = EIGHTOCTET = EIGHT

Cations Sodium – Na – What is the electron configuration?Sodium – Na – What is the electron configuration? What type of ion will it form and how?What type of ion will it form and how?

Anions What is the electron configuration of fluorine?What is the electron configuration of fluorine? What type of ion will it form and how?What type of ion will it form and how?

Types of Bonds Ionic BondsIonic Bonds Electrostatic InteractionsElectrostatic Interactions Net charge TransferNet charge Transfer Covalent BondsCovalent Bonds Sharing of one of more electronSharing of one of more electron

Ionic Bonds A large difference in electro-negativities will lead to an IONIC BOND between two atomsA large difference in electro-negativities will lead to an IONIC BOND between two atoms

Formation of an Ionic Bond Na ( [Ne] 3s 1 ) + Cl ( [Ne] 3s 2 3p 5 ) Na + ([Ne]) + Cl - ([Ne] 3s 2 3p 6 ) Note that each ion formed has a noble gas configuration of electrons -- Na + has the Ne configuration of 10 electrons and Cl - has the Ar configuration of 18 electrons – Na + /Ne and Cl - /Ar are said to be ISOELECTRONIC Such electron arrangements are very stable, and accounts for the change in electron structure that Na and Cl atoms undergo.

A small difference in electro-negativities will lead to a covalent bond between two atoms. Covalent Bonds

CH 4 Electronegativity of C = 2.55 electronegativity of H = 2.20  EN = = 0.35

Electronegativity and bond type

Properties of Ionic Compounds High Melting pointsHigh Melting points Soluble in polar solvents (e.g. water)Soluble in polar solvents (e.g. water) Insoluble on non-polar solvents (e.g. hexane)Insoluble on non-polar solvents (e.g. hexane) Molten ionic compounds conduct electricityMolten ionic compounds conduct electricity Aqueous solutions conduct electricityAqueous solutions conduct electricity Formed between elements of quite different electro negativities (metals and non-metals)Formed between elements of quite different electro negativities (metals and non-metals)

Properties of Covalent Compounds Usually low melting pointUsually low melting point Insoluble in polar solventsInsoluble in polar solvents Soluble in non-polar solventsSoluble in non-polar solvents Liquid and molten compounds do not conduct electricityLiquid and molten compounds do not conduct electricity Aqueous solutions are poor conductorsAqueous solutions are poor conductors Often formed between elements of similar electro negativitiesOften formed between elements of similar electro negativities

Properties of Metals & Alloys To be done on the boardTo be done on the board