Bonding

Covalent

Ionic

Metallic

Remember Lewis Dot Diagrams

Symbol of the element surrounded by dots that represent valence electrons

Whe atoms bond they either share or transfer electrons to complete their valence shell

To draw valence electrons of atoms that are prepared to bond …

Covalent BondingAtoms share electrons

2 electrons per bond

The electrons “count” for both atoms that are being bonded together.

Atoms want to be involved with 8 electrons

All electrons get paired

Covalent bonds form molecules

Usually two nonmetals

Difference in electronegativity is < 1.7

Examples

F2

Cl2HCl

H2O

NH3

CH4

C2H6

Examples with double / triple bonds

O2

N2

C2H4

C2H2

CO2

Other examples

Remember: the central atom is the first non-H in the formula

PCl3

Energy changes in bonding

Whenever any bond is formed, energy is releasedIt takes energy to break bondsExothermic reactions release more energy than they absorbEndothermic reactions absorb more energy than they releaseTriple bonds are stronger than double or single bonds. They are therefore the most stableSingle bonds are the weakest covalent bonds

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Properties of Molecules

Soft

Low melting points

Poor conductors of heat and electricity

Where do the electrons spend the most time in the

bonds?Determined by the electronegativities of the atoms which are bonded together

The electrons spend more time with the atom which is more electronegative

When the atoms have a difference in electronegativity of 0.1 1.6 the bond is called polar

No difference in electronegativity means the bond is nonpolar

How am I ever going to remember that?

S ymmetrical

N onpolar

A symmetrical

P olar

Covalent Networks

Network solids

Macromolecules

Covalently bonded atoms are linked into a giant network throughout the entire sample.

More practice with Lewis Dot Diagrams

SO2

N2H4

N2O4

CCl2F2

H2CO

Covalent bonding leads to…

Covalent bonding forms molecules

Properties of moleculesSoftPoor conductors of heat and electricityLow melting points

Another Look at Polar and Nonpolar Bonds

Look at the electronegativities

Remember that polar versus nonpolar is all about the symmetry

SNAP

Think about the distribution of the electrons

The different types of covalent bonds

There are single, double, and triple bondsOnly refers to the number of electrons

being shared between the two atoms2,4,6 – can’t have any more than 6

All covalent bonds can be polar or nonpolar

The story of the mooch

A type of covalent bond called “Coordinate Covalent bonding”

Basically – a bond is formed where both electrons come from only one of the atoms

Where do they usually come from?

The two examples of coordinate covalent

bonding

NH3 + H+ NH4+

H2O + H+ H3O+

In both cases the H ion bonds to the central atom using the other atom’s electrons

Overview of covalent bonding

Sharing electrons

Molecules and their properties

Drawing Lewis Dot Diagrams

Polar vs. nonpolar SNAP

Network covalent Properties Macromolecules

Coordinate Covalent Mooch

The shapes of molecules

TetrahedronTrigonal pyramidTrigonal planarBentLinearThese are the only 5 options for your molecules, others exist, but you won’t see them

Other types of bonding

Ionic bonding – transfer of electronsLarge difference ( 1.7) in

electronegativityPositive and negative ions formed by a

transfer of electron(s)

Metallic bonding – a sea of electronsThe valence electrons are able to move

around independent of their individual atoms

Lewis Dot Diagrams of Ionic Compounds

Write symbol for metal and nonmetalMetal gets the charge written with itNonmetal getsChargeBracketsElectronsCharge

Write in as many as you need

Examples

Draw the electron dot diagram for the compoundWrite the ionic formula Write the regular formulaLithium and fluorine; magnesium and sulfur; sodium and oxygen; calcium and bromine; potassium and fluorine; barium and iodine; strontium and oxygen