Covalent bonds, Polar Covalent bonds, Polar bonds, and Ionic Bonds bonds, and Ionic Bonds

Students will identify the various Students will identify the various types of bonds and the physical types of bonds and the physical properties associated with them.properties associated with them.

What is a covalent bond?What is a covalent bond?

A bond between two nonmetal atoms A bond between two nonmetal atoms where the electrons are shared. where the electrons are shared.

Why do atoms form covalent Why do atoms form covalent bonds? bonds?

So they can have the same number of So they can have the same number of electrons as the nearest noble gas.electrons as the nearest noble gas.

Electronegativity Electronegativity Turn to page 362 Turn to page 362

What is Electronegativity What is Electronegativity

The ability for an atom to attract electrons The ability for an atom to attract electrons to itself in a covalent bond. to itself in a covalent bond.

• The higher the Electronegativity, the more The higher the Electronegativity, the more powerful pull it has on the electrons.powerful pull it has on the electrons.

Electronegativity TrendElectronegativity Trend

What is the trend?. What is the trend?.

Metals and non-metals do not form Metals and non-metals do not form covalent bonds covalent bonds

Nonmetals pull so much more than Nonmetals pull so much more than metals that when paired together, the metals that when paired together, the electron is transferred to the nonmetal.electron is transferred to the nonmetal.

That is why in NaCl, the sodium has a That is why in NaCl, the sodium has a positive charge.positive charge.

And the chlorine has a negative charge.And the chlorine has a negative charge.

Tug of WarTug of War

Atoms try to pull electrons to themselves. Electronegativity Atoms try to pull electrons to themselves. Electronegativity is the measure of how strong the pull is.is the measure of how strong the pull is.

So the strong guy pulls the electron So the strong guy pulls the electron more than the weak guymore than the weak guy

In this case H is positive and F is negative.In this case H is positive and F is negative.

The Three Types of BondsThe Three Types of Bonds

Polar Bond vs. Polar MoleculePolar Bond vs. Polar Molecule

Do all molecules that have polar bonds Do all molecules that have polar bonds become polar molecules?become polar molecules?

No. Because the molecule may be No. Because the molecule may be balanced due to opposing forces. balanced due to opposing forces.

Ionic or CovalentIonic or Covalent

Determine if the combinations are ionic or covalent.Determine if the combinations are ionic or covalent.Na-O Na-O C-N C-N H-FH-F

Most IonicMost Ionic

Na-O Na-O C-N C-N

Put the combinations in order of most ionic Put the combinations in order of most ionic to most covalentto most covalent

Solution: Find the Electronegativity Solution: Find the Electronegativity difference. difference.

Na-O =3.5 - .9 = 2.6, C-N = 3.0 -2.5 = .5Na-O =3.5 - .9 = 2.6, C-N = 3.0 -2.5 = .5

Na-O is the most ionic between these twoNa-O is the most ionic between these two

Bonding Effects Physical PropertiesBonding Effects Physical Properties

For Example, ionic bonds areFor Example, ionic bonds are

Crystalline solids Crystalline solids

They have high melting and boiling They have high melting and boiling points points

They conduct electricity when melted They conduct electricity when melted

Many soluble in water but not in Many soluble in water but not in non-polar liquidsnon-polar liquids

ionic substances dissolve in water ionic substances dissolve in water because water is polarbecause water is polar

CovalentCovalent

Gases, liquids, or solids Gases, liquids, or solids (made of molecules) (made of molecules)

Low melting and boiling points Low melting and boiling points

Poor electrical conductors in all phases Poor electrical conductors in all phases

Many soluble in non-polar liquids but not Many soluble in non-polar liquids but not in water in water

Show Video from Weber tubeShow Video from Weber tube

Chemical Cocktail

Hydrogen BondingHydrogen Bonding

Hydrogen Bonding is an especially Hydrogen Bonding is an especially powerful type of polar-covalent bonding.powerful type of polar-covalent bonding.

If only happens in bonds with: If only happens in bonds with:

hydrogen and oxygenhydrogen and oxygen

Hydrogen and nitrogenHydrogen and nitrogen

And hydrogen and fluorine.And hydrogen and fluorine.

ExamplesExamples

COCO

HH22OO

CHCH44

NHNH33

Watch Video on hydrogen Bonding

Guessing Boiling PointsGuessing Boiling Points

Which will have the highest boiling point? Which will have the highest boiling point? CHCH44 or CH or CH33-OH? -OH?

Explain: The CHExplain: The CH33-OH is very polar -OH is very polar

because it has hydrogen bonding.because it has hydrogen bonding.

When a molecule is polar the molecules When a molecule is polar the molecules stick to each other causing the boiling stick to each other causing the boiling point to be high.point to be high.

The Bigger a molecule is the higher The Bigger a molecule is the higher the boiling point isthe boiling point is

Which will have the highest boiling point? Which will have the highest boiling point? CHCH44 or H or H33C-CHC-CH33

Explain: Since ethane is a larger molecule Explain: Since ethane is a larger molecule it should have the highest boiling pointit should have the highest boiling point

Life Without Hydrogen BondingLife Without Hydrogen Bonding

Water wouldn’t boil at +100Water wouldn’t boil at +100ooC, it would C, it would boil at -120boil at -120ooCC

All HAll H22O on earth would be gas. O on earth would be gas.

No snow. Therefore, no skiing. No snow. Therefore, no skiing.

That wouldn’t hurt Utah’s economy That wouldn’t hurt Utah’s economy because there would be no Utah because there would be no Utah

Life Without Hydrogen BondingLife Without Hydrogen Bonding