Electronegativity and Polarity

1
Electronegativity and Polarity

• Section 9-5

2
Electron affinity

• Tendency of atom to accept electron
• Usually increases as atomic numbers increase
  within period
• Usually decreases as atomic number increases
  within a group

3
Linus Pauling

• Developed scale of electronegativity
• Figure 9-15, pg 263
• Fluorine has the highest 3.98
• Francium has the lowest 0.7
• Noble gases are not given (0)

4
Electron Affinity tells us

• Character and type of bond
• Never completely ionic or covalent
• Sharing is not always completely equal

5
Ionic Bond

• Large differences in electronegativity indicate
  that electrons are transferred

6
Nonpolar covalent bonds

• Difference in electron affinity of atoms involved
  is very small
• Electrons shared fairly equally

7
Identical Atoms

• Difference in electronegativity is 0
• Electrons are shared equally.

8
Polar Covalent Bonds

• Unequal sharing
• Electron tug-of-war
• Stronger affinity greater strength

9
Differences

• Less than 0.4 nonpolar covalent bond
• 0.4 1.7 polar covalent bond
• Greater than 1.7 ionic bond

10
Examples

• H and Br
• 2.20 and 2.96 0.76 polar covalent
• C and O
• 2.55 and 3.44 0.89 polar covalent
• Li and F
• 0.98 and 3.98 3.00 ionic bond

11
Solubility of Polar Molecules

• Like dissolves like
• Polar (and ionic) compounds are soluble in polar
  substances
• Nonpolar only soluble in non-polar substances

12
Properties of Covalent Compounds

• Van der Waals forces weak forces of attraction
  between individual molecules

13
Types of Intermolecular Forces

• Nonpolar
• Weak attraction
• Dispersion or induced dipole
• Polar
• Stronger attraction
• Dipole-dipole force
• Hydrogen bond
• Very strong
• Between H and another dipole

14
Physical properties

• Melting/boiling points lower than ionic
• Many are gases at room temp
• Non-conductors of heat or electricity
• Extremely hard
• Due to the intermolecular forces!!