G10 4.5: Electronegativity and Polarity

Electronegativity and

Polarity

Lesson 5

Focus Question

How does molecular shape affect the way that covalent compounds are held together?

New Vocabulary

polar covalent bond

nonpolar covalent bond

Multiple Choice

Electronegativity is...

• how good an atom is at attracting electrons

• the ability of an atom to lose electrons

• the energy required to remove an electron from a specific atom

• how easy it is to make friends. 

Review Vocabulary

electronegativity: the relative ability of an atom to
attract electrons in a chemical bond

Electronegativity and Bond Character

• The scale of electronegativities allows chemists

to evaluate the affinity of specific atoms in a
compound to electrons.

• Excluding noble gases, electronegativity

increases with increasing atomic number within a
period and decreases with increasing atomic
number within a group.

• Noble gases are not listed because they generally

do not form compounds (Non reactive).

• The table on the next slide lists the

electronegativity values.

Electronegativity and Bond Character

Multiple Choice

Why does electronegativity decrease as you go down a group?

• As you go down a group, the outer electrons are further away from the nucleus

• As you go down a group, the nucleus is less able to attract electrons in a bond

• Both of these

• None of these

Multiple Choice

What does electronegativity do as you go across a period?

• decrease

• no pattern

• stay the same

• increase

Multiple Choice

What elements have zero electronegativity?

• metals

• nonmetals

• metalloids

• noble gases

Multiple Choice

Which element has a higher electronegativity value?

• Niobium

• Tin

• Cadmium

• Iodine

Multiple Choice

Which element has a lower electronegativity value?

• Calcium

• Barium

Electronegativity and Bond Character

Bond Character
• The table lists the character and type of

chemical bond that forms with differences in
electronegativity.

Electronegativity and Bond Character

• Unequal sharing of electrons results in a polar

covalent bond.

• Bonding is often not clearly ionic or covalent.
• The graph summarizes the range of chemical

bonds between two atoms.

Multiple Choice

Covalent bonds occur between....

• Metals

• Metalloids

• Non-metals

• Actinide

Multiple Choice

Covalent bonds occur when.....

• Atoms share valence electrons

• Atoms transfer valence electrons

• Atoms lose electrons and become ions

• Atoms dance to the Macarena

Multiple Choice

What type of covalent bond is characterized by an unequal sharing of electrons?

• Ionic Bond

• Polar Covalent Bond

• Non-Polar Covalent Bond

• Covalent Bond

Multiple Choice

What type of covalent bond is characterized by an equal sharing of electrons

• Non-Polar Covalent Bond

• Covalent Bond

• Ionic Bond

• Polar Covalent Bond

Polar Covalent Bonds

• When a polar bond forms, the shared electron pair or

pairs are pulled toward one of the atoms.

• The electrons spend more time around that atom than

the other atom.

• This results in partial charges at the ends of the bond.

Polar Covalent Bonds

Molecular Polarity
• Covalently bonded molecules are either polar or nonpolar.

• Non-polar molecules are not attracted by an electric field.

• Polar molecules align with an electric field.

Polar Covalent Bonds

Polarity and Molecular Shape
• Compare water, H2O, and CCl4:

• Both bonds are polar. and

The molecular shapes, determined by VSEPR, are both bent and tetrahedral.

O–H bonds are asymmetric in water. There is a definite positive end and a definite negative end making it polar.

C – Cl bonds are symmetrical in CCl4. Electric charge measured at any distance from the center is identical on all sides. Partial charges are balanced, and are nonpolar.

Multiple Choice

Water is a polar molecule because of unequal sharing of electrons between the oxygen and hydrogen atoms bonded together.

• true

• false

Multiple Choice

In a polar covalent bond, the atom with a negative charge is less electronegative.

• true

• false

Properties of Covalent Compounds

Intermolecular Forces
• Covalent bonds between atoms are strong, but

attraction forces between molecules are weak.

• The weak attraction forces are known as intermolecular

forces, or van der Waals forces.

• The forces vary in strength but are weaker than the

bonds in a molecule or ions in an ionic compound.

Properties of Covalent Compounds

• Non-polar molecules exhibit a weak dispersion force, or

induced dipole.

• The force between two oppositely charged ends of two

polar molecules is a dipole-dipole force. The more polar
the molecule, the stronger the dipole-dipole force.

• A hydrogen bond is an especially strong dipole-dipole

force between a hydrogen end of one dipole and a
fluorine, oxygen, or nitrogen atom on another dipole.

Properties of Covalent Compounds

Solubility of Polar Molecules
• Solubility is the property of a substance’s ability to

dissolve in another substance.

• Polar molecules and ionic substances are usually soluble

in polar substances.

• Non-polar molecules dissolve only in non-polar

substances.

Properties of Covalent Compounds

Forces and Properties
• Many physical properties are due to intermolecular

forces.

• Weak forces result in the relatively low melting and

boiling points of molecular substances.

• Many covalent molecules are relatively soft solids.

• Molecules can align in a crystal lattice, similar to ionic

solids but with less attraction between particles.

Multiple Choice

Compounds have _________________ properties, compared to the elements that form them.

• similar

• different

Multiple Choice

A triple covalent bond forms when two atoms share ____________.

• 2 pair of electrons

• 4 total electrons

• 3 pair of electrons

• 3 total electrons

Multiple Choice

Polar substances like water are good at dissolving ___________.

• other polar substances

• non polar substances

• all substances

• no substances

Multiple Choice

What do we call a covalent bond where electrons are shared UNEVENLY or UNEQUALLY?

• Ionic

• Polar Covalent

• Nonpolar Covalent

• Van der Waals Force

Multiple Select

Which of the following is true about Covalent (non-polar) bonds? (select ALL true options)

• High melting point

• Low melting point

• Can dissolve in water

• Cannot dissolve in water

• Can conduct electricity

Multiple Choice

Compared to ionic compounds, molecular compounds generally have...

• good conductivity

• greater densities

• more chemical bonds

• a low boiling point

Multiple Choice

Compared to ionic compounds, molecular compounds generally have...

• stronger chemical bonds

• poor conductivity

• a high melting point

• lower densities

Covalent Network Solids

• Solids composed of only atoms interconnected by a

network of covalent bonds are called covalent network
solids.

• Quartz and diamonds are two common examples of

network solids made of cabon covalent bonds.

• Network solids are typically brittle, nonconductors of

heat or electricity, and extremely hard.

Multiple Choice

What element are diamond and graphite made up of?

• A.     Sodium

• B.     Carbon

• C.     Carbon dioxide

• D.     Silicon

Think of the Quiz answers before moving

to the next slide

Quiz

Br, Li, Fe, As

D

Br, As, Fe, Li

C

Fe, As, Li, Br

B

Li, Fe, As, Br

A

Which shows the correct order of elements from the
highest electronegativity to the lowest electronegativity?

1.

Quiz

Br, Li, Fe, As

D

Br, As, Fe, Li

C

Fe, As, Li, Br

B

Li, Fe, As, Br

A

Which shows the correct order of elements from the
highest electronegativity to the lowest electronegativity?

1.

CORRECT

Quiz

mostly covalent

D

nonpolar covalent

C

polar covalent

B

mostly ionic

A

What type of bond will form between identical
atoms with an electronegativity balance of zero?

2.

Quiz

mostly covalent

D

nonpolar covalent

C

polar covalent

B

mostly ionic

A

What type of bond will form between identical
atoms with an electronegativity balance of zero?

2.

CORRECT

Quiz

nonpolar covalent

D

mostly ionic

C

mostly covalent

B

polar covalent

A

If two atoms have a electronegativity difference
greater than 1.7, what type of bond are they likely
to form?

3.

Quiz

nonpolar covalent

D

mostly ionic

C

mostly covalent

B

polar covalent

A

If two atoms have a electronegativity difference
greater than 1.7, what type of bond are they likely
to form?

3.

CORRECT

Quiz

weak intermolecular
forces between
molecules

D

strong ionic bonds in an
ionic compound

C

strong intermolecular
forces between
molecules

B

strong covalent bonds
between atoms

A

Which of the following best describes van der
Waals forces?

4.

Quiz

weak intermolecular
forces between
molecules

D

strong ionic bonds in an
ionic compound

C

strong intermolecular
forces between
molecules

B

strong covalent bonds
between atoms

A

Which of the following best describes van der
Waals forces?

4.

CORRECT