Transcript 10.3_Electronegativity

Chapter 10 Structures of Solids
and Liquids
10.3
Electronegativity and Polarity
Basic Chemistry
Copyright © 2011 Pearson Education, Inc.
1
• Electronegativity: Trends Among Groups and
Periods of the Periodic Table
• http://educationportal.com/academy/lesson/electronegativitytrends-among-groups-and-periods-of-theperiodic-table.html
Basic Chemistry
Copyright © 2011 Pearson Education, Inc.
2
Electronegativity
Electronegativity
1. is the relative ability of atoms to attract shared
electrons
2. is higher for nonmetals, with fluorine as the
highest with a value of 4.0
3. is lower for metals, with cesium and francium as
the lowest with a value of 0.7
4. increases from left to right going across a period
on the periodic table
5. decreases going down a group on the periodic
table
Basic Chemistry
Copyright © 2011 Pearson Education, Inc.
3
Electronegativity
• The most commonly used method
of calculation is that originally
proposed by Linus Pauling,
commonly referred to as the
Pauling scale.
• Linus Pauling's book, How to Live
Longer and Feel Better,advocated
very high intake of Vitamin C.
Basic Chemistry
Copyright © 2011 Pearson Education, Inc.
4
Some Electronegativity Values for
Group A Elements
Basic Chemistry
Copyright © 2011 Pearson Education, Inc.
5
Electronegativity
Electronegativity
generally
decreases
increases
downelement
from
a group
left(4.0)
to right
for
Fluorine is the most
electronegative
representative
across
a period elements
Basic Chemistry
Copyright © 2011 Pearson Education, Inc.
Learning Check
Using the periodic table, predict the
order of increasing electronegativity
for the elements O, K, and C.
Basic Chemistry
Copyright © 2011 Pearson Education, Inc.
7
Solution
The metal K on the left of Period 4 has the lowest
electronegativity of the three elements.
The nonmetal O on the upper right of Period 2
has the highest electronegativity.
The nonmetal C, which is on the left of O in the
periodic table, has a lower electronegativity
than O, but a higher electronegativity than K.
Order of increasing electronegativity: K, C, O
Basic Chemistry
Copyright © 2011 Pearson Education, Inc.
8
Nonpolar Covalent Bonds
A nonpolar covalent bond
• occurs between nonmetal atoms
• consists of an equal (or almost equal) sharing of electrons
• has a zero (or close to zero) electronegativity difference of 0.0 to 0.4
Examples:
Atoms
Electronegativity
Difference
NN
3.0 - 3.0 = 0.0
ClBr
3.0 - 2.8 = 0.2
HSi
2.1 - 1.8 = 0.3
Basic Chemistry
Type of Bond
Nonpolar covalent
Nonpolar covalent
Nonpolar covalent
Copyright © 2011 Pearson Education, Inc.
9
Polar Covalent Bonds
A polar covalent bond
• occurs between nonmetal atoms
• consists of atoms that share electrons unequally
• has an electronegativity difference range of 0.5 to 1.7
Examples:
Atoms
Electronegativity
Difference
OCl
3.5 - 3.0 = 0.5
ClC
3.0 - 2.5 = 0.5
OS
3.5 - 2.5 = 1.0
Basic Chemistry
Type of Bond
Polar covalent
Polar covalent
Polar covalent
Copyright © 2011 Pearson Education, Inc.
10
Comparing Nonpolar vs Polar
Covalent Bonds
Basic Chemistry
Copyright © 2011 Pearson Education, Inc.
11
Ionic Bonds
An ionic bond
• occurs between metal and nonmetal ions
• is a result of electron transfer
• has a large electronegativity difference (1.8 or more)
Examples:
Atoms
Electronegativity
Difference
ClK
3.0 – 0.8
= 2.2
NNa
3.0 – 0.9
= 2.1
SCs
2.5 – 0.7
= 1.8
Basic Chemistry
Type of Bond
Ionic
Ionic
Ionic
Copyright © 2011 Pearson Education, Inc.
12
Electronegativity and Bond Types
Basic Chemistry
Copyright © 2011 Pearson Education, Inc.
13
Predicting Bond Types
Basic Chemistry
Copyright © 2011 Pearson Education, Inc.
14
Learning Check
Use electronegativity differences to classify each of
the following bonds as nonpolar covalent (NP),
polar covalent (P), or ionic (I):
A bond between
A. K and N
B. N and O
C. Cl and Cl
D. H and Cl
Basic Chemistry
Copyright © 2011 Pearson Education, Inc.
15
Solution
Atoms in
Bond
A. K and N
B. N and O
C. Cl and Cl
D. H and Cl
Electronegativity
Difference
2.2
0.5
0.0
0.9
Basic Chemistry
Type of
Bond
ionic (I)
polar covalent (P)
nonpolar covalent (NP)
polar covalent (P)
Copyright © 2011 Pearson Education, Inc.
16
Polar Molecules
A polar molecule
• contains polar bonds
• has a separation of positive and negative charge called a
dipole indicated by a dipole arrow
• has dipoles that do not cancel
Basic Chemistry
Copyright © 2011 Pearson Education, Inc.
17
Nonpolar Molecules
A nonpolar molecule
1) may contain identical atoms (nonpolar bonds)
2)
may have a symmetrical arrangement of polar bonds
that cancel dipoles
Basic Chemistry
Copyright © 2011 Pearson Education, Inc.
18
Determining Molecular Polarity
The polarity of a molecule is determined from its
1. electron-dot formula
2. shape
3. polarity of the bonds
4. dipole cancellation
Basic Chemistry
Copyright © 2011 Pearson Education, Inc.
19
Polar or Nonpolar?
Which one is polar: CO2 or H2O?
H2O
Basic Chemistry
CO2
Copyright © 2011 Pearson Education, Inc.
Dipole Moment and Polarity
Basic Chemistry
Copyright © 2011 Pearson Education, Inc.
Molecular Polarity
• Explains solubility of
substances
– Likes dissolve in likes.
• Provides information on a substance’s
chemical and physical properties
– Melting points and boiling points
H2O
Bp: 100 oC
Basic Chemistry
vs.
CH4
Bp: -161 oC
Copyright © 2011 Pearson Education, Inc.
Learning Check
Identify each of the following molecules as
(P) polar or (NP) nonpolar:
A. PBr3
B. HBr
C. Br2
D. SiBr4
Basic Chemistry
Copyright © 2011 Pearson Education, Inc.
23
Solution
Identify each of the following molecules as
(P) polar or (NP) nonpolar:
A.
B.
C.
D.
PBr3
HBr
Br2
SiBr4
Basic Chemistry
(P) pyramidal; dipoles don’t cancel; polar
(P) linear; one polar bond (dipole); polar
(NP) linear; nonpolar bond; nonpolar
(NP) tetrahedral; dipoles cancel; nonpolar
Copyright © 2011 Pearson Education, Inc.
24
• Halogens are highly reactive, and as such can be harmful or lethal to
biological organisms in sufficient quantities. This high reactivity is due
to the atoms being highly electronegative due to their high effective
nuclear charge. They can gain an electron by reacting with atoms of
other elements. Fluorine is one of the most reactive elements in
existence, attacking otherwise inert materials such as glass, and
forming compounds with the heavier noble gases. It is a corrosive
and highly toxic gas. The reactivity of fluorine is such that if used or
stored in laboratory glassware, it can react with glass in the presence
of small amounts of water to form silicon tetrafluoride (SiF4). Thus
fluorine must be handled with substances such as Teflon (which is
itself an organofluorine compound), extremely dry glass, or metals
such as copper or steel which form a protective layer of fluoride on
their surface
Basic Chemistry
Copyright © 2011 Pearson Education, Inc.
25
• Nonbonding pairs affect molecular polarity;
they pull the electron density strongly.
Basic Chemistry
Copyright © 2011 Pearson Education, Inc.
26
MOLECULAR GEOMETRY AND VSEPR
Valence Shell Electron
Pair Repulsion
•
VSEPR is used to predict the molecular
geometries of compounds based on the
number of electron groups attached to the
center atom of the molecule.
•
Most important factor in determining the
geometry is minimizing the relative repulsion
between electron pairs.
•
Molecules’ or ions’ geometry reflects
arrangement that favors minimal electron
repulsion.
Basic Chemistry
Copyright © 2011 Pearson Education, Inc.