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Chemistry Unit 3Chemical Bonds

Valence ElectronsDot Diagrams

Oxidation numbersTypes of Bonds

PolyatomicsTransition elements

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Valence ElectronsThe number of electrons in the outer energy level involved in bonding.Equal to the ‘group number’ (except 3-12).Found in loop and cross diagrams.

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Dot DiagramsUsed to show the valence electrons with the symbol. .

H And N. .. ...

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WB Practice!AluminumBoron

SulfurCalcium

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Oxidation Numbers•The number of electrons that an element would like to gain or lose to complete its outer valence shell.•All atoms and compounds want to have a complete outer shell.•8 electrons (An Octet) completes any outer shell.•They come from the valance electrons.

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Oxidation NumbersFrom valence electrons:

Valence 1-3 want to lose.Valence 5-7 want to gain.Valence of 4 can go either way.

So… H, Li, and Na have oxidation numbers of 1+ because they would like to give one electron away to be ‘stable’.

While… F, Cl and Br has oxidation numbers of 1- because they would like to get one electron to be ‘stable’.

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Types of BondsIonic:

Where electrons are lost and gained between atoms.Mainly between metals and non-metals.Uses the Oxidation number

Covalent:Where electrons are shared between atoms.Between two non-metals.You must be given the number of each element used.

For BONDING:Elements to RIGHT of the stair step are NON-metalElements to the LEFT of the stair step are METAL

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Examples of Ionic Compounds

Sodium and Chlorine: (Na 1+ and Cl 1-) is NaCl

Potassium and Bromine: (K 1+ and Br 1-) is KBr

Magnesium and Oxygen: (Mg 2+ and O 2-)

is MgOCalcium and Sulfur: (Ca 2+ and S 2-)

is CaS

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Ionic Bonds DemoHydrogen and Oxygen:

So it takes 2 Hydrogen to bond with one oxygen.

Calcium and Chlorine:

So it takes 2 Cl to bond with 1 Ca)

1+ 2-HO 2+

1-Ca Cl

2H2O

1CaCl2

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2

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Ionic Bonds - NOTICEIn the final answer – if the subscripts would match, we leave them off.The positive oxidation always comes first.Pay very close attention to capital and lower case and the placement of the subscript.

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Ionic Bond Practice

Combine: Potassium and SulfurMagnesium and NitrogenCalcium and PhosphorousAluminum and Chlorine

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Examples of Covalent

1 Carbon and 1 Oxygen is CO

1 Carbon and 2 Oxygen is CO2

1 Phosphorous and 3 Chlorine is

PCl3

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Covalent Bond PracticeCombine:

1 Silicon and 4 Fluorine2 Nitrogen and 3 Sulfur1 Hydrogen and 1 Bromine2 Bromine

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PolyatomicsCovalent compounds that are “pre-formed” with unique names and charges (oxidations).They can and will ionically bond with other compounds and elements.

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Poly Oxidation 1- (FS)Name

AcetateBicarbonateChlorateHydroxideNitrateNitriteCyanide

FormulaC2H3O2

HCO3

ClO3

OHNO3

NO2

CN

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Poly OXIDATION 2- (FS)Name

CarbonateChromatePeroxideSulfateSulfiteSilicate

FormulaCO3

CrO4

O2

SO4

SO3

SiO3

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Poly – Other Oxidations (FS)Oxidation -

Name3- Phosphate1+ Ammonium1+ Ammonia1+ Hydronium0 Methane

FormulaPO4

NH4

NH3

H3OCH4

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Polyatomic Ionic ExamplesCombine:

Aluminum (Al 3+) and Sulfate (SO4 2-)Al2(SO4)3

Potassium (K 1+) and Nitrate (NO3 1-) KNO3

Ammonium (NH4 1+) and Chlorine (Cl 1-)NH4Cl

Ammonium (NH4 1+) and Nitrate (NO3 1-)NH4NO3

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Polyatomic PracticeCombine:

Barium and HydroxideCalcium and SulfateAmmonium and HydroxideLithium and Nitrate

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Transition Elements

The transition elements get their name because they have variable oxidation numbers.Their oxidation numbers are always positive.You are told or given a transition elements oxidation number with a roman numeral.They will bond Ionically with other elements and compounds.

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Transition Ionic Examples

Combine:Copper (I) and Oxygen (Cu2O) since Cu 1+ and O 2-

Iron (III) and Chlorine (FeCl3) since Fe 3+ and Cl 1-

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Transition Ionic PracticeCombine:

Lead (II) and CarbonateGold (III) and SulfurNickel (II) and NitrateTin (II) and Fluorine