Search for notes by fellow students, in your own course and all over the country.
Browse our notes for titles which look like what you need, you can preview any of the notes via a sample of the contents. After you're happy these are the notes you're after simply pop them into your shopping cart.
Document Preview
Extracts from the notes are below, to see the PDF you'll receive please use the links above
INTRODUCTORY
CHEMISTRY-CHM 50
Chapter 10
Chemical
Bonding
If you have any
funny chemistry
memes or jokes
to share with the
class please do
so ☺
Chemical Formulas
• A chemical formula
expresses the number and
types of atoms in a molecule
...
Writing Chemical Formulas
• The number of each type of atom in a molecule is
indicated with a subscript in a chemical formula
...
(H2O not H2O1)
• A molecule of the vitamin niacin has 6 carbon
atoms, 6 hydrogen atoms, 2 nitrogen atoms, and 1
oxygen atom
...
• Antifreeze has the chemical formula C2H4(OH)2
...
• Antifreeze has a total of 10 atoms
...
Atomic Elements
– exist in nature with single atoms as their basic units
...
Molecular Elements
– two atoms of the same element bonded together
“diatomic molecules”)
(called
3
...
4
...
• They are hydrogen (H2), nitrogen (N2), oxygen
(O2), and the halogens, F2, Cl2, Br2, and I2
...
Memorize these
7 elements!!!
Molecules vs
...
ex) H2O
Formula Unit
•Smallest unit of a substance composed of at least one metal atom
and at least one nonmetal atom
...
• We use one dot for each
valence electron
...
Here is the method for writing the
electron dot formula
...
• Core electrons are found close to the nucleus
...
• It is the valence electrons that are responsible
for holding two or more atoms together in a
chemical bond
...
• There are two ways in which an atom may achieve
an octet
...
• This “electrostatic attraction” is similar to the
attraction between opposite poles on two magnets
...
The
structure for NaCl,
ordinary table salt, is
shown here
...
How can Lewis
diagrams help?
K
K
K
P
K
K
K
3-
P
K3 P
23
Lewis Structures for Ionic Compounds
Example #2:
What is the Lewis Structure of Aluminium (Al) and Oxygen (O)?
Example #3:
What is the Lewis Structure of Strontium (Sr) and Sulfur (S)?
Lewis Structures for Molecular
Compounds
• In the beginning of the chapter, we drew electron
dot formulas for atoms
...
• We will now draw electron dot formulas for
molecules (also called Lewis structures)
...
25
Guidelines for Drawing Lewis
Structures of Molecules
1
...
2
...
3
...
4
...
(Make molecule as symmetrical as possible)
26
Guidelines for Drawing Lewis
Structures of Molecules (cont)
5
...
The only
exception is hydrogen which only needs two
electrons
...
If there are not enough electron pairs to provide
each atom with an octet, move a nonbonding
electron pair between two atoms that already
share an electron pair
...
Nonbonding electrons (lone pairs):
•Electrons that are only on one atom
...
(another trick is that usually the least electronegative element
that is not hydrogen is the central atom …more on this
later)
29
What is the Central Atom?
What is the central atom in each of the following
examples?
1
...
POCl2
3
...
First, count the total number of valence electrons: oxygen has 6 and
each hydrogen has 1 for a total of 8 electrons [6 + 2(1) = 8 e-]
...
The number of electron pairs is 4 [8/2 = 4]
...
Place 4 electron pairs around the
central oxygen atom
...
We can then place the two hydrogen
atoms in any of the four electron pair
positions
...
31
Electron Dot Formula for H2O
• To simplify, we represent bonding electron pairs
with a single dash line called a single bond
...
O H
H
32
Electron Dot Formula for SO3
1
...
24/2 = 12 pairs of valence electrons
3
...
4
...
5
...
6
...
Electron Dot Formula Examples
Draw the electron dot formula for a molecule of PI3
34
Electron Dot Formula Examples
Draw the electron dot formula for a molecule of
SiHClBrI
More Complicated Lewis Structures
Note: When there are too many atoms to fit around
the central atom, hydrogen usually goes on the
outside
...
• The double bond can be placed
between the sulfur and any of the 3 oxygen
atoms and the structural formula can be
shown as any of the following
...
37
Polyatomic Ions
• Single atoms with positive or negative charges
are called monoatomic ions
...
ex) NH4+
38
Electron Dot Formula for NH4+
1
...
We must subtract one electron for the positive charge
...
2
...
3
...
39
Electron Dot Formula for CO32What is the Electron dot formula for CO32- ?
Electron Dot Formula for SeO32What is the Electron dot formula for SeO32-?
Polar Covalent Bonds
• Covalent bonds result from the sharing of valence
electrons
...
• When one of the atoms holds the shared electrons
more tightly, the bond is polarized
...
42
Electronegativity
• Each element has an innate ability to attract
valence electrons
...
• Linus Pauling devised a method for measuring the
electronegativity of each of the elements
...
43
Electronegativity
• Electronegativity increases as you go left to right
across a period
...
44
Electronegativity Values
45
Electronegativity Differences
• Using the electronegativity values on your periodic table,
we see the electronegativity of H is 2
...
0
...
0 – 2
...
9), the bond in H – Cl is polar
...
This will give the Cl atom a slightly negative
charge and the H atom a slightly positive charge
...
• The negatively charged atom is indicated by the
symbol δ–, and the positively charged atom is
indicated by the symbol δ+
...
δ+
H – Cl δ–
47
Nonpolar Covalent Bonds
• What if two atoms in a covalent
bond have the same or similar
electronegativities?
• The bond is not polarized and it is
a nonpolar covalent bond
...
4, it is considered a
nonpolar bond
...
4
Nonpolar Covalent
H–C
0
...
0
Polar Covalent
H–F
> 2
...
Textbooks vary with these ranges
• The degree of bond
polarity is a continuous
function
...
a) B
P
b) C
S
c) H
Br
50
Coordinate Covalent Bonds
• A covalent bond resulting from one atom donating
a lone pair of electrons to another atom is called a
coordinate covalent bond
...
51
Coordinate Covalent Bonds
A oxygen atom can bond to a HIO molecule,
forming HIO2
...
Check Your Knowledge
Examples:
• classify bonds as nonpolar covalent, polar covalent or ionic
...
1
...
CO
3
...
• Atoms bond in such a way as to have eight
electrons in their valence shell – the Octet Rule
...
• Ionic bonds are formed between a cation and an
anion
...
55
Summary Continued
• Electron Dot Formulas helps us to visualize the
arrangements of atoms in a molecule
...
• Electronegativity is a measure of the ability of an
atom to attract electrons in a chemical bond
...
56
Homework
Chapter 5 Readings:
Sections 5
...
4 (pages 131–137)
Chapter 10 Readings:
Sections 10
...
5 and 10