CHEMICAL BONDING•COVALENT BONDS• IONIC BONDS•METALLIC BONDS

Reflection (pg 62)

• What is a metallic bond?• Compare/contrast it to ionic/covalent bond

Metallic Bonds

• How atoms are held together in the solid.

• Metals hold onto there valence electrons very weakly.

• Think of them as positive ions floating in a sea of electrons.

Sea of Electrons

+ + + ++ + + +

+ + + +

• Electrons are free to move through the solid.

• Metals conduct electricity.

Characteristic of Metallic Bonds

• High electrical and thermal conductivity

• Malleable, ductile, high luster.

• Great amount of heat needed to break these bonds.

IONIC BONDING

When an atom of a nonmetaltakes one or more electrons

from an atom of a metalso both atoms end up with

eight valence electrons

IONIC BONDING

IS THE COMPOUND AN IONIC COMPOUND?

METAL NONMETAL

SUBSCRIPTS

IONIC BOND FORMATION

IONIC BONDING

ION – any atom with more orless electrons that it is

supposed to have*

*Remember that the number of electronsis supposed to be equal to the number ofProtons if the atom has a neutral charge

IONIC BONDING

Metals will tend to lose electrons and become

POSITIVE CATIONS

Normal sodium atom loses one electron to become sodium ion

Na+1 is called a sodium ion

The +1 symbol means it

has lost one electron

IONIC BONDING

IONIC BONDING

Nonmetals will tend to gain electrons and become

NEGATIVE ANIONS

Normal chlorine atom gains an electron to become a chloride ion

Cl-1 is called a chloride ion

The -1 symbol means it

has gained one electron

IONIC BONDING

Properties of Ionic Compounds• Hard, brittle solids.• Strongest bond.• Most dissolve in water• Conduct electricity when

dissolved in water.• High melting/ boiling points-

because of strong forces between ions.

Crystalline structure

+

+

+ +

+

+

++

+

--

--

- --

--

The POSITIVE CATIONS stick to the

NEGATIVE ANIONS, like

a magnet.

COVALENT BOND FORMATION

When one nonmetal shares one or more electrons with an atom of another nonmetal so both atoms end up with eight valence electrons

COVALENT BONDING

IS THE COMPOUND A COVALENT COMPOUND?

NONMETAL NONMETAL

YES since it is made of only nonmetal elements

Polar Bonds• When two different atoms are connected,

the atoms may not be shared equally.• This is a polar covalent bond.

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Nonpolar Bonds• When the atoms in a bond are the same, the

electrons are shared equally.• This is a nonpolar covalent bond.

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Characteristics of Covalent Bonds• Represented by Lewis structures• Strong bond but weaker than Ionic

bonds• Low melting points & boiling points• Most do not dissolve in water• Do not conduct electricity.• Usually in a gas state at room

temperature

Covalent bonds• Monatomic: contains one atom• Diatomic: contains two atoms

BrINClHOFBromine (Br2), Iodine (I2), Nitrogen (N2), Chlorine (Cl2), Hydrogen (H2), Oxygen (O2), Fluorine (F2)

You must have these memorized!!!!• Polyatomic: contains more than one atom.

Octet Rule• Octet rule: atoms tend to gain, lose, or share

electrons until they are surrounded by 8 valence electrons (4 electron pairs).

• Exceptions:• Hydrogen forms bonds in which it is surrounded

by only two electrons.• Boron tends to form bonds in which it is

surrounded by 6 electrons.• Main group elements in period 3 and up can form

bonds with expanded valance shells.

Lewis structure rules• 1.Write the element symbol. Around this

draw dots—one for each valence electron.• 2. The dots sould be spread over four sides.

Dots are not paired until all sides have at least one dot.

• 3. It does not matter on which side dots are placed. Example- Hydrogen can be drawn in four ways:

H H H H

Lewis structure rules

• 4. The number of valence electrons is equal to the group number for groups 1 and 2. In groups 13 to 18, subtract 10 and that is the number of valence electrons.

Multiple bonds in Lewis Structures

• Molecules containing carbon (C), nitrogen (N), and oxygen (O) may form multiple bonds.

• The need for multiple bonds becomes obvious if there are not enough valence electrons to complete octets by adding unshared electron pairs.

Double bonds• Produced by sharing two pairs of electrons

between two atoms.

C C CCH

H

H

HH

H

H

H

Triple Bonds• Produced by sharing three pairs of electrons

between two atoms.

N

MOLECULAR SHAPES

OFCOVALENT

COMPOUNDS

VSepR tHEORY

What Vsepr means

Since electrons do not like each other, because of their negative charges, they orient themselves as far apart as possible, from each other.

This leads to molecules having specific shapes.

Things to remember

•Atoms bond to form an Octet (8 outer electrons/full outer energy level)

•Do NOT forget all electron pairs, including unshared electron pairs!!!

Linear

• The central atom is represented by A and the atoms bonded to the central atom are B.

• The molecule AB2 is linear

• Bond Angle = 180°

EXAMPLE:

BeF2

Trigonal Planar

• The molecule AB3 makes an equilateral triangle.

• Bond Angle = 120°

EXAMPLE:

GaF3

Tetrahedral

• The molecule AB4 makes the shape of a tetrahedral (kind of looks like a pyramid).

• Bond Angle = 109.5°

EXAMPLE:

CH4