Chemical Bonding

Ionic Bonding in Review

• Ionic compounds tend to form as crystals– These crystals have a specific shape

• Arrangement of the ions that make up the ionic compound

• Ratio of the ions in the compound• Size of the ions themselves

– NaCl – cubic

– Al2O3 – Ruby – Hexagonal

Crystal Structure

Crystal Structure

Properties of Ionic Compounds

• High Melting Points

• Poor conductor when they are in the solid state

• Good conductor when they are melted

• Tend to shatter when they are struck with a hammer

Covalent Bonding

• A transfer of electrons does not tend to take place between nonmetals

• These nonmetals tend to share their electrons to complete their valence (outer) shells

• When atoms share electrons they form a covalent bond– One pair shared – single bond (hydrogen)– Two pairs shared – double bond (oxygen)– Three pairs shared – triple bond (nitrogen)

Molecules

• A molecule is a neutral group of atoms that are joined by one or more covalent bonds– They are held together by the attraction

between the shared electrons and the protons in each nucleus

Covalent Bonding

• Ways to represent covalent bonds– Electron Dot– Structural Formula– Space-filling model– Electron Cloud Model

Models for Covalent Molecules

Unequal Sharing

• Elements to the right have a greater attraction for electron than those on the left

• Elements at the top of the group have a greater attraction for electrons than those below

• Polar Covalent Bond – covalent bond in which the electrons are not shared equally– The atom with the greater attraction for the electrons

has a partial negative charge and the atom with the weaker attraction for electrons has a partial positive charge

Unequal Sharing

How Do we Know?

• If a molecule has only two atoms (different elements) it will always be polar

• If a molecule has more than two atoms then the answer is not obvious– If the molecules are linear they will be

nonpolar (usually contain double or triple bonds)

Attraction between molecules

• The attraction between polar molecules is stronger than the attraction between nonpolar molecules– Water

Naming Molecular Compounds

• The name of a molecular compound describes the type and number of atoms in a molecule of the compound– Most metallic element appears first (further

left or if in the same group closer to the bottom

– Name of second element changed to end in IDE

– Use prefix to indicate the number atoms of each element

Prefixes to use

Examples

• We never use a prefix on the first element if it contains only one atom (never use mono at the beginning)

• CO2 - Carbon Dioxide

• P2F4 – Diphorphorous tetrafluoride

• CO – Carbon monoxide

• CF4 – Carbon tetrafluoride

Naming Binary Ionic Compounds

• Give the name of the cation (metal) first– No change to the name – just the name of the element

• Give the name of the anion (nonmetal) second changing the end to “ide”– Chlorine = chloride– Fluorine = fluoride– Bromine = bromide– Oxygen = oxide– Nitrogen = nitride– Phosphorous = phosphide– Iodine = iodide– Sulfur = sulfide

• NOTE – THE NUMBERED SUBCRIPTS AREN’T USED WHEN NAMING BINARY IONIC COMPOUNDS!

Practice Naming

• Give the correct name to the following binary ionic compounds– Li2S– MgO– CaCl2– SrF2

– KBr– Na3P– Al2O3

Answers

• Li2S – Lithium Sulfide

• MgO – Magnesium Oxide

• CaCl2 – Calcium Chloride

• SrF2 – Strontium Fluoride

• KBr – Potassium Bromide

• Na3P – Sodium Phosphide

• Al2O3 – Aluminum Oxide

Practice Formula Writing

• Write the chemical formula for the following binary ionic compounds– Lithium Nitride– Rubidium Fluoride– Sodium Iodide– Beryllium Nitride– Magnesium Sulfide– Calcium Bromide– Aluminum Nitride– Barium Oxide

Answers

• Lithium Nitride – Li3N• Rubidium Fluoride - RbF• Sodium Iodide - NaI• Beryllium Nitride – Be3N2

• Magnesium Sulfide - MgS• Calcium Bromide – CaBr2

• Aluminum Nitride - AlN• Barium Oxide - BaO

Naming when there are transition metals

• Some of the transition metals exist as ions with more than one charge– Copper can be + 1 or + 2– Iron can be + 2 or + 3– Lead can be +2 or +4– Chromium can be +2 or + 3– Titanium can be +2, +3, or + 4– Mercury can be +1 or +2

Continued

• When these elements appear in an ionic compound we must use a Roman numeral after the name of the cation to indicate which form (charge) of the ion it is when we are naming these ionic compounds. The Roman number tells us the number of the positive charge (Again remember we must have a total net charge of zero) – Copper (I) oxide = Cu2O

– Copper (II) oxide = CuO

Now the tricky part continued

• When asked to give the formula remember that the Roman numeral tells us the charge on the cation.– Iron (III) oxide– Mercury (II) chloride– Lead (IV) nitride

Polyatomic ions

SiO3-2 - Silicate

Naming Ionic Compounds Containing Polyatomic Ions

• Works the same as simple binary ionic compounds except that in place of the single element anion you give the name of the polyatomic anion

• CaCO3

• Calcium Carbonate

• NaOH

• Sodium Hydroxide

Writing Formulas for Ionic Compounds containing polyatomic ions

• The net charge must be zero for the ions involved

• Work it the same way as the others• List the cation and the polyatomic ion

involved with their charges• If you need more than one polyatomic ion

to balance out the compound you must place the polyatomic ion in parenthesis and put the subscript after the parenthesis

Examples

• Potassium Carbonate

• K2CO3

• Calcium Hydroxide

• Ca(OH)2

• Copper (II) Sulfate

• CuSO4