01_01_06

7/30/2019 01_01_06

1/44

Chapter 1

Structure Determines Properties

7/30/2019 01_01_06

2/44

1.1

Atoms, Electrons, and Orbitals

7/30/2019 01_01_06

3/44

Protons

positively charged

mass = 1.6726 X 10-27 kg

Neutrons

neutral

mass = 1.6750 X 10-27 kg

Electrons

negatively charged

mass = 9.1096 X 10-31 kg

+

Atoms are composed of

7/30/2019 01_01_06

4/44

Atomic number (Z) = number of protons in nucleus(this must also equal the number of electrons

in neutral atom)

Mass number (A) = sum of number of protons

+ neutrons in nucleus

X

Z

A

Atomic Number and Mass Number

7/30/2019 01_01_06

5/44

Schrdinger combined the idea that an electron

has wave properties with classical equations

of wave motion to give a wave equation for the

energy of an electron in an atom.

Wave equation (Schrdinger equation) gives a

series of solutions called wave functions ( ).

Schrdinger Equation

7/30/2019 01_01_06

6/44

Only certain values of are allowed.

Each corresponds to a certain energy.

The probability of finding an electron at aparticular point with respect to the nucleus is

given by 2.

Each energy state corresponds to an orbital.

Wave Functions

7/30/2019 01_01_06

7/44

Figure 1.1 Probability distribution (2) for anelectron in a 1s orbital.

7/30/2019 01_01_06

8/44

Figure 1.2 Boundary surfaces of a 1s orbitaland a 2s orbital.

1s 2s

A boundary surface encloses the region

where the probability of finding an electron

is high

on the order of 90-95%

7/30/2019 01_01_06

9/44

Each orbital is characterized by a unique

set of quantum numbers.

The principal quantum numbernis a wholenumber (integer) that specifies the shell and is

related to the energy of the orbital.

The angular momentum quantum numberisusually designated by a letter (s,p, d, f, etc)

and describes the shape of the orbital.

Quantum Numbers

7/30/2019 01_01_06

10/44

s Orbitals are spherically symmetric.

The energy of an s orbital increases with the

number ofnodal surfaces it has.

A nodal surface is a region where the probability

of finding an electron is zero.

A 1s orbital has no nodes; a 2s orbital has one;

a 3s orbital has two, etc.

s Orbitals

7/30/2019 01_01_06

11/44

No two electrons in the same atom can have

the same set of four quantum numbers.

Two electrons can occupy the same orbitalonly when they have opposite spins.

There is a maximum of two electrons per orbital.

The Pauli Exclusion Principle

7/30/2019 01_01_06

12/44

1s 2s 2p

H

He

Principal quantum number (n) = 1

Hydrogen Helium

Z= 1 Z= 2

1s 1 1s 2

First Period

7/30/2019 01_01_06

13/44

p Orbitals are shaped like dumbells.

Are not possible forn = 1.

Are possible forn = 2 and higher.

p Orbitals

7/30/2019 01_01_06

14/44




There are three p orbitals for each value

ofn (when n is greater than 1).

p Orbitals

7/30/2019 01_01_06

15/44






p Orbitals

7/30/2019 01_01_06

16/44






p Orbitals

7/30/2019 01_01_06

17/44

Principal quantum number (n) = 2

1s 2s 2p

Be 4

B 5

C 6

Li 3

Z

Second Period

7/30/2019 01_01_06

18/44

1s 2s 2p

O 8

F 9

Ne 10

N 7

Z

Second Period

7/30/2019 01_01_06

19/44

1.2

Ionic Bonds

7/30/2019 01_01_06

20/44

An ionic bond is the force of electrostaticattraction between oppositely charged ions

Cl

(anion)

Na+ (cation)

Ionic Bonding

7/30/2019 01_01_06

21/44

Ionic bonds are common in inorganic chemistry

but rare in organic chemistry.

Carbon shows less of a tendency to form cationsthan metals do, and less of a tendency to form

anions than nonmetals.

Ionic Bonding

7/30/2019 01_01_06

22/44

7/30/2019 01_01_06

23/44

In 1916 G. N. Lewis proposed that atoms

combine in order to achieve a more stable

electron configuration.

Maximum stability results when an atom

is isoelectronic with a noble gas.

An electron pair that is shared betweentwo atoms constitutes a covalent bond.

The Lewis Model of Chemical Bonding

7/30/2019 01_01_06

24/44

Covalent Bonding in H2

H . H.

Two hydrogen atoms, each with 1 electron,

can share those electrons in a covalent bond.

H: H

Sharing the electron pair gives each hydrogen

an electron configuration analogous to helium.

7/30/2019 01_01_06

25/44

Covalent Bonding in F2

Two fluorine atoms, each with 7 valence electrons,

can share those electrons in a covalent bond.

Sharing the electron pair gives each fluorine an

electron configuration analogous to neon.

..

..F. F.: :

..

..

F: F: :..

..

..

..

7/30/2019 01_01_06

26/44

The Octet Rule

The octet rule is the most useful in casesinvolving covalent bonds to C, N, O, and F.

F: F: :..

..

..

..

In forming compounds, atoms gain, lose, orshare electrons to give a stable electron

configuration characterized by 8 valence

electrons.

7/30/2019 01_01_06

27/44

C .. .

.F:..

...

Combine carbon (4 valence electrons) and

four fluorines (7 valence electrons each)

to write a Lewis structure for CF4.

: F:..

..

C: F:....

: F:

..

..: F:

..

..

The octet rule is satisfied for carbon and

each fluorine.

Example

7/30/2019 01_01_06

28/44

It is common practice to represent a covalent

bond by a line. We can rewrite

: F:..

..C

: F:..

..

: F:..

..: F:..

..

..

CF

F

F

F

..

......: :

: :

: :

..

as

Example

7/30/2019 01_01_06

29/44

1.4

Double Bonds and Triple Bonds

7/30/2019 01_01_06

30/44

C: : :O..

:O..

: : C :O..

O..

:

: : :N:C:H :NCH

Carbon dioxide

Hydrogen cyanide

Inorganic Examples

7/30/2019 01_01_06

31/44

Ethylene

Acetylene: : :C:C:H H CCH H

C: :C..

H : :..

H

HH

C C

H H

HH

Organic Examples

7/30/2019 01_01_06

32/44

7/30/2019 01_01_06

33/44

An electronegative element attracts electrons.

An electropositive element releases electrons.

Electronegativity

Electronegativity is a measure of the ability

of an element to attract electrons toward

itself when bonded to another element.

7/30/2019 01_01_06

34/44

1.0

Na

0.9

Li Be B C N O F

1.5

Mg

1.2

2.0

Al

1.5

2.5

Si

1.8

3.0

P

2.1

3.5

S

2.5

4.0

Cl

3.0

Electronegativity increases from left to right

in the periodic table.

Electronegativity decreases going down a group.

Pauling Electronegativity Scale

7/30/2019 01_01_06

35/44

The greater the difference in electronegativity

between two bonded atoms; the more polar the

bond.

Generalization

nonpolar bonds connect atoms of

the same electronegativity

HH :N N:F:....F: ....

7/30/2019 01_01_06

36/44

The greater the difference in electronegativity

between two bonded atoms; the more polar the

bond.

Generalization

polar bonds connect atoms ofdifferent electronegativity

:O C

F:..

..H

O..

..H

H O:.. ..

7/30/2019 01_01_06

37/44

Electrostatic potential maps show the charge

distribution within a molecule.

Electrostatic Potential Maps

Red is negative charge;

blue is positive.

F:

..

..H

Solid

surface

7/30/2019 01_01_06

38/44





blue is positive.

F:

..

..H

Transparent

surface

7/30/2019 01_01_06

39/44





blue is positive.

F:..

..

H

LiH

7/30/2019 01_01_06

40/44

7/30/2019 01_01_06

41/44

The order in which the atoms of a

molecule are connected is called its

constitution orconnectivity.

The constitution of a molecule mustbe determined in order to write a

Lewis structure.

Constitution

7/30/2019 01_01_06

42/44

Condensed structural formulas

Lewis structures in which many (or all)

covalent bonds and electron pairs are

omitted.

H

O

C C C

H H H

H

HH : :

H

can be condensed to:

CH3CHCH3

OH

(CH3)2CHOHor

7/30/2019 01_01_06

43/44

Bond-line formulas

CH3CH2CH2CH3 is shown as

CH3CH2CH2CH2OHis shown as OH

Omit atom symbols. Represent

structure by showing bonds between

carbons and atoms other thanhydrogen.

Atoms other than carbon and hydrogen

are called heteroatoms.

7/30/2019 01_01_06

44/44

Bond-line formulas

H Cl

C

C

H2C

H2C

CH2

CH2

HH

is shown as

Cl

Omit atom symbols. Represent

structure by showing bonds between

carbons and atoms other than

hydrogen.

Atoms other than carbon and hydrogen

Documents

01_01_06