Covalent Compounds & Molecule Shapes

2014

I. IONIC COMPOUNDS>How are Ionic Compounds Made?>Made of metal and nonmetal (or sometimes,

polyatomic ions may be present)>Electrons are transferred>Individual particles are called formula units

Examples: (salts) aluminum chloride, copper II nitrate

>Writing Formulas and Names of Ionic CompoundsWhich elements?

>Metal names don’t change while nonmetals end in “-ide”.

>Polyatomic ion names don’t change either.

>Many transition metals require a roman numeral to

indicate their oxidation number

>Polyatomic ions are written inside parenthesis

>Oxidation numbers are used to determine subscripts.

>Writing Formulas and Names of Ionic Compounds>Oxidation numbers are used to determine subscripts.>Examples:

Aluminum chloride Tin IV Oxide Al+3 Cl-1 Sn+4 O-2

x1 x3 x2 x4Al Cl3 Sn2O4 -- > reduces to SnO2 really

Sodium sulfate Na+1 SO4-2 barium chlorate Ba+2 ClO3

-1

x2 x1 x1 x2Na2 (SO4) Ba(ClO3)2

II. COVALENT COMPOUNDS

>How are Covalent Compounds Made?

>Made of 2 nonmetals or sometimes hydrogen

and a nonmetal

>Electrons are shared

>Individual particles are called molecules

>Examples: water, sugar, carbon dioxide,

dinitrogen pentoxide

>STEPS for Writing Names of Covalent Compounds

a. Write the name of the first element (IF there is MORE THAN ONE atom of the first element, use a prefix!)

b. Identify the number of atoms of the second element, write the prefix that indicates how many of that element, then….

c. Write the name of the second element and change its ending to “-ide”

PREFIXES for step a and b….

1 = mono- 4 = tetra- 7 = hepta- (some use septa-)

2 = di- 5 = penta- 8 = octa-

3 = tri- 6 = hexa- 9 = nona-

10 – deca-

That’s enough!

EXAMPLES:

SiO2 = silicon dioxide

(one silicon on first name….NO Prefix)

P4O10 = tetraphosphorus decoxide

(drop the prefix’s “a” when using oxygen)

N2F5 = dinitrogen pentafluoride

(the first name’s ending doesn’t change)

>Writing Formulas for Covalent Compounds• Use the prefixes to find how many atoms of the

element• Do NOT reduce the formula, even if the

subscripts “could” be reduced!

(hydrogen peroxide for cuts) dihydrogen dioxide = H2O2

III. COMPARING PROPERTIES OF IONIC AND COVALENT BONDS / COMPOUNDS

Ionic Bonds / Compounds

•Made of metal & nonmetal generally•Electrons transferred (e- lost by one, gained by the other)•HIGH boiling point•HIGH melting point (can’t melt it in the kitchen; it’s solid)•CONDUCT electricity (when melted or as a solid)•Crystalline structure Ex. stalactites and stalagmites in caves•Often is a SALT •Nearly always dissolves in water (Electrolyte)•1 particle is called a Formula Unit

III. COMPARING PROPERTIES OF IONIC AND COVALENT BONDS / COMPOUNDS

Covalent Bonds / Compounds

•Made of 2 nonmetals•Electrons are shared•LOW boiling point

(turn to gas easily or IS a gas)•LOW melting point •Do NOT conduct electricity •Many do NOT dissolve in water (nonelectrolyte)•1 particle is called a Molecule

. IV. COVALENT BONDS>Why do they form?

• Nonmetals try to get 8 valence electrons like noble gases have.

Exceptions: • Hydrogen actually tries to get 2 valence electrons, not 8.• Beryllium actually tries to get 4 valence electrons, not 8.• Boron actually tries to get 6 valence electrons, not 8.

. IV. COVALENT BONDS>Why do they form?

• Nonmetals try to get 8 valence electrons like noble gases have.• Exceptions:

• Hydrogen actually tries to get 2 total valence electrons, not 8.• Beryllium actually tries to get 4 total valence electrons, not 8.• Boron actually tries to get 6 total valence electrons, not 8.

• 2 nonmetals can’t both “gain” electrons, so they “share” electrons instead

• As a compound, the elements have less energy and, therefore, are more stable.

Get ready to learn how to predict the shapes of molecules:

Lewis Dot Structures of Elements--- dots represent only the valence electrons

Be Li B C N O F Ne

1 2

3

6

4 7

5

8

. Types of Covalent Bonds that can formPolar = unequal sharing of electrons One element has a stronger pull on the electrons ( more pull on e- = more electronegative)Nonpolar = equal sharing of electrons The elements making the bond have equal (or very nearly equal) pull on the electrons

Covalent Bonds can be:

A single bond is when 2 electrons are shared.

A double bond is when 4 electrons are shared

A triple bond is when 6 electrons are shared

H-H

. Molecular ModelsModels help us demonstrate the 3-D image of a compoundEven though the atom is too small to see, we can predict its molecular geometry (shape).

What molecule shapes can happen? What do they look like? ………………………….

Linear

2 or 3 bonded atoms

No lone electrons

180o Bond Angle

Symmetrical shape

Example: BeCl2

MOLECULE POLARITY:

IF both “outside atoms” are the same = NONPOLAR (same atoms pull electrons the same)

But, if the “outside atoms” are different = POLAR (electrons are pulled unevenly to one side)

Bent3 bonded atoms1 or 2 lone pairs of electrons104.5o Bond AngleThough not visible in the model, a lone pair of electrons takes up more space than a single atom (Electrons repel each other!)Asymmetrical Example: SO2 (left picture--not common!), H2O (right picture 2 lone pairs = more common)

Bent3 bonded atoms1 or 2 lone pairs of electronsAsymmetrical shape

MOLECULE POLARITY:

“Bent” molecules are always POLAR.

Trigonal Planar4 bonded atomsNo lone electrons120o Bond AngleSymmetrical shapeExample: BCl3

MOLECULE POLARITY:

IF both “outside atoms” are the same = NONPOLAR (same atoms pull electrons the same)

But, if the “outside atoms” are different = POLAR (electrons are pulled unevenly to one side)

Trigonal Pyramidal (or Triangular Pyramidal)4 bonded atoms1 lone pair of electrons107.3 o Bond AngleThough not visible in the model, a lone pair of electrons takes up more space than a single atom (Electrons repel each other!)Asymmetrical shapeExample: PH3

Trigonal Pyramidal (or Triangular Pyramidal)4 bonded atoms1 lone pair of electronsAsymmetrical shape

MOLECULE POLARITY:

Trigonal Pyramidal molecules are always POLAR. (electrons are pulled unevenly to one side)

Tetrahedral5 bonded atomsNo lone electrons109.5o Bond AngleSymmetrical shapeExample: CH4

MOLECULE POLARITY:

IF both “outside atoms” are the same = NONPOLAR (same atoms pull electrons the same)

But, if the “outside atoms” are different = POLAR (electrons are pulled unevenly to one side)

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