Compounds
Chapter 2
1
Types
yp of Matter
„
Homogeneous matter has the same
appearance, composition, and properties
throughout.
throughout
„
Heterogeneous matter has visibly different
phases which can be seen
seen, or properties that
vary through the substance.
2
Classification of Matter
3
Classification of Matter
„
A mixture is two or more pure substances that can
be separated by physical changes or method.
„
Pure substances have a distinct set of physical
and chemical properties and cannot be separated
by physical changes.
4
Pure Substance
„
A compound is a pure substance that can be
decomposed by a chemical change or method into
two or more elements. Two or more elements
together.
„
An element is a pure substance with its own set of
physical and chemical properties that cannot be
decomposed into simpler substances. Simplest form
of matter.
matter (Chapter One)
5
Classifyy
„
Water
„
Al i
Aluminum
foil
f il
„
Air
„
Oxygen
yg
„
Cake
6
Why do Atoms Combine?
„
To mimic or acquire the stability of the
noble gases.
„
Stability is due to number of valence
electrons noble gases contain
contain.
„
Atoms off elements
At
l
t will
ill acceptt or give
i
away electrons to become more stable.
7
Reactivityy of Elements
„
What will elements do to have the same number of electrons
as the noble gases?
„
What will Sodium do?
(b)
11p
p+
11 e-
Na
Æ
(c)
11p
p+
10 e-
Na+ + e8
Reactivity of Elements
„
What will potassium do?
19
p+
19
e-
Potassium Atom
… In
general:
„ M1A
- 1e
1 -
Argon has 18 e-
19 p+
18 e-
Potassium Ion (K+)
Cation
Æ M1A+1 + 1e9
Formation of Ions
„
„
What about Magnesium?
What’s the closest noble g
gas to magnesium?
g
Neon has 10 e-
12 p+
12
e-
-2e12 p+
10 e-
Magnesium Ion (Mg+2)
Magnesium Atom
Cation
„
M2A Æ M2A+2 + 2e10
Where do the electrons go?
g
„
„
Must find an element that might need some extra
electrons.
What will bromine do? Who’s the closest noble
gas?
Krypton has 36 e-
35 p+
35
+ 1e-
e-
35 p+
36 e-
Bromide Ion (Br-)
Bromine Atom
Anion
„
X7A + 1e- Æ X7A-1
11
Formation of Monatomic Ions
Group 1A-3A Metals Group 5A-7A Nonmetals
Na → Na+ + 1 e-
N + 3 e- → N3-
Ca → Ca2+ + 2 e-
S + 2 e- → S2-
Al → Al3+ + 3 e-
F +
Cations
Lose or give
awayy electrons
e- → F Anions
Accept
electrons
Cation + Anion = Ionic Compound
12
Ionic Compounds
„
Form when electrons are transferred from
one element
l
t to
t the
th other.
th
„
Metals – give away electrons and become
cations
„
Nonmetals – accept electrons from metals
13
To write the formula of the ionic compound first predict the
charge of each element and then write the neutral formula.
Positive has to cancel negative. Practice the following:
a) Ions that come from elements sodium and fluorine
b) Ions that come from elements calcium and bromine
c) Ions that come from elements magnesium and nitrogen
14
Naming Ionic Compounds
„
Write the name of the cation (metal ion). The name of a
cation is the same as the metal name.
„
Write the name of the anion (nonmetal ion) by
changing the ending of the element name to ide.
ide
Ca2+ = calcium ion
S2- = sulfide ion
Name the previous exercise
15
Transition Metals
„
„
As metals they give away electrons.
Theyy g
give away
y a variable number of electrons
from:
„
„
„
„
1e- to 7e-
For most transition metals the highest number of
electrons corresponds to the roman numeral in
th column.
the
l
Most common charges are +2 and +3.
G the
Get
h charge
h
off the
h metall ffrom the
h anion
i to
which it’s combine.
16
Exceptions
p
to the Variable Charges
g
„
Three exceptions:
… Ag
gives away 1e- to form Ag+
… Zn
gives away
g
y 2e- to form Zn+2
… Cd
gives
g es away
a ay 2e
e- to form
o Cd+2
17
Predict the Correct Chemical Formula for:
„
Co+3 and sulfide
„
A) CoS
„
Cadmium and iodide
„
A) CdI
b) Co2S
b) CdI2
c) Co3 S2
c) Cd2I
d) Co2 S3
c) Cd2I3
18
Naming
g Ionic Compounds
p
of Transition Metals
„
Add the charge of the metal as a Roman
numeral in parenthesis. cobalt (II) fluoride.
What is the name of FeCl2
„
Mn2O3
„
a) Magnesium (II) oxide
c) Manganese (III) oxide
b) manganese (II) oxide
d) manganese oxide
19
Polyatomic
y
Ions
„
Group of elements that together have a charge.
20
A few more p
polyatomic
y
ions
„
Group of elements that together have a charge.
ClO4- Perchlorate Æ One more O: Charge is the same
ClO3- Chlorate “Parent” polyatomic ion (looks like Nitrate)
ClO2- Chlorite Æ One less O: Charge
g is the same
ClO- or OCl- ---> Hypochlorite One less O: Charge is the same
21
What’s the Chemical Formula?
„
Boron hydroxide
„
Palladium (IV) hypochlorite
„
Ammonium sulfite
22
From Formulas to Names
„
Fe2(SO4)3
„
a. iron (II) sulfate
„
Pb(NO3)4
b. iron (III) sulfite
c) iron sulfate
d. iron (III) sulfate
23
Properties of Ionic Compounds
•Solids
Solids at Room Temperature
•High Melting and Boiling Point
•When dissolved in water the
solutions
l ti
are conductors
d t
off
electricity.
•Strongest type of
intermolecular force: ion-ion
24
Sharing
of Electrons
25
Lewis Dot Structures
Valence electrons are represented as dots around the symbol of an
element. Electrons are not paired unless necessary
Noble gases have eight valence electrons in their outer shell or energy level.
26
The Octet Rule
„
Atoms want to have eight electrons in the outer shell,
as the stable noble g
gases.
„
Atoms may gain, lose or share electrons to obtain
eight electrons in the outer shell.
„
Hydrogen and helium can hold only two electrons in
their outer shell.
„
What is the Lewis structure of fluoride?
27
Covalent Compounds
p
„
Share electrons to complete their octet.
„
Formed by nonmetals interacting or attracted to
other nonmetals.
„
The bond forms by overlap of electron clouds.
„
Represented as a tug-of-war or holding hands.
„
Simplest representation is a molecule
28
C
Covalent
l tC
Compounds
d
H
Î
„
H
+
„
F
+
F
Î
„
O
+
O
Æ
Reason for the existence of diatomic elements
29
Covalent Bonds
„
Single
Si
l Covalent
C
l t Bond
B d - Sharing
Sh i off ttwo
electrons between two atoms.
„
Double Bond – Sharing of four electrons
between two atoms.
„
Triple Bond – Sharing
g of six electrons between
two atoms.
30
Number of Covalent Bonds Formed by
Nonmetal Atoms
Lewis Dot Structure
Number of Bonds:
4
3
2
1
0
Lone Pair or Nonbonding Electrons – not used in bond
31
Naming Covalent Compounds
„
„
Unlike ionic compounds nonmetals combine to
other nonmetals in different proportions.
CO
vs.
CO2
„
carbon monoxide vs. carbon dioxide
„
We need prefixes to indicate how many.
32
N i C
Naming
Covalent
l tC
Compounds
d
1
2
3
4
5
mono
di
tri
tetra
penta
6
7
8
9
10
hexa
hepta
p
octa
nona
deca
Only for covalent compounds
33
Let’s
Let
s Try It!
N
Name
each
h bi
binary molecule
l l
a) BF3
b)) SCl6
c) CoI2
d) P2O5
34
Lewis Structure
What molecules look like in
Three Dimensions
Three-Dimensions
Lewis Structure Drawings
„
„
„
„
„
„
Calculate total number of valence electrons.
Connect all atoms to the central atom with single bonds.
Subtract valence electrons used (2e- /bond)
Complete the octet of outside atoms using lone pairs.
If left over electrons available, give to central atom.
Check that central atom has a complete octet. If less than
eight electrons, take two electrons from outside atom and
form a double bond.
Formal Charges
g
For each atom
„ F.
F C.
C = Column
Col mn # - (# dots + # bonds)
„
„
Expanded octet – Larger atoms in period 3
or below can accommodate more than 8 e-
GRAMS AND MOLES
Mass of Chemical Compounds
p
„
„
Formula or Molecular Weight is the sum of the
atomic mass of the elements in the formula
formula.
Sodium chloride (NaCl) has a formula weight of
58.5 amu
Na+
Cl-
NaCl
22.99 amu
35.45 amu
58.44 amu
amu = atomic mass unit is the mass of an atom
39
Avogadro’s
Avogadro
s Number of Molecules
„
1 molecule is at microscopic
p level
„
1 mole is at macroscopic level
„
1 mole = 6.02
6 02 x 1023 atoms or molecules
1 mole is the most important unit of measurement
for chemists because the relation exist within
chemical formulas or chemical equations.
q
40
Molar Mass
„
The mass (in grams) of one mole (6.02 x1023 ) of
substance.
„
Molar mass can be used to convert between the number
of moles of a particular compound and its mass.
6.02x1023
Atoms or Molecules
„
1 mole
Molar Mass in grams
What is the molar mass of silver nitrate?
41
„
How
o many
a y moles
o es o
of ssilver
e nitrate
aea
are
e used if 85
85.7
grams are used in an experiment?
„
A) 0.505 mol
b) 1.98 mol
c) 0.557 mol
d) 0.331 mol
How many molecules of silver nitrate are in the
above
b
question?
ti ?
„
„
42
Practice
What is the mass of 0.315 moles of sodium bicarbonate?
How many moles of sodium bicarbonate are in 24.54 g of it?
a) 2061 mol
b) 0.092 mol
c) 0.292 mol
d) 1 mol
H many molecules
How
l l off sodium
di
bicarbonate
bi b t are contained
t i d in
i 24.54g?
24 54 ?
43