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Chemistry - Unit 4

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Mark Holcomb

on 20 February 2015

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Transcript of Chemistry - Unit 4

Unit 4
1 2 3 4 5 6 7 8
Exception
Question: Why do elements bond?
Answer: To satisfy the octet rule!
Octet rule
– atoms will gain, lose, or share electrons to obtain a full valence shell (2 for 1st shell, 8 for all other shells)

Carbon would like to: Nitrogen would like to: Oxygen would like to:
Gain 4
Gain 3
Gain 2
(H and He follow the Duet Rule)
+1 +2 +3 4 -3 -2 -1 0
+/-
Charges for Each Group
Determining Charges from Valence Electrons
Is it easier for...
Li to lose 1 electron or gain 7?
Mg to lose 2 electrons or gain 6?
Al to lose 3 electrons or gain 5?
C to lose 4 electrons or gain 4?
N to lose 5 electrons or gain 3?
O to lose 6 electrons or gain 2?
F to lose 7 electrons or gain 1?
Ne to lose any electrons?
Keep in mind...
Electrons have a NEGATIVE charge
Chapter 2 & 3 Review
DON'T FORGET!!!
Chemical compounds are vastly different from the elements that make them up!!
Ex. Sodium (Na) is a soft silver colored solid metal that is explosively reactive with air and water. Chlorine (Cl ) is a green poisonous gas. BUT when bonded together, sodium chloride (NaCl) is an edible white crystalline solid.

2
+ =
Sodium metal + Chlorine Gas Sodium Chloride
(Table Salt)
Explosive!!!
Poison!!!
Food???
2Na + Cl 2NaCl
2
NOTE: You MUST know how they bond so you can write formulas and reactions (Unit 5).

+
Hydrogen Gas + Oxygen Gas Water
2H + O 2H O
2 2
2
Ex. Hydrogen (H ) is a low-density colorless explosive gas. Oxygen (O ) is a colorless reactive gas needed for breathing. BUT when bonded together, water (H O) is a clear liquid.

2
2
2
Valence Electrons
are electrons in the outermost shell.
Lewis Dot Diagram
Types of Bonding
+1 +2 +3
4

-3 -2 -1 0
+/-
+
-
Think of the Periodic Table as a bar magnet .
+
-

Left side is positive
Right side is negative
Opposites attract!!!
Therefore, elements of the opposite charge like to attract!!!
?
Metalloids...
Below
the stairstep line are more
metal
than
non-metal
.
Above
the stairstep line are more
non-metal
than
metal
.
Ionic Bonding Covalent Bonding Metallic Bonding
Metal
+
Non-metal

Non-Metal
+
Non-Metal

Metal
+
Metal

Binary Polyatomic
(2 different elements) (3 or more different elements)
Use Greek prefixes to name!
Mono-
Di-
Tri-
Tetra-
Penta-

Hexa-
Hepta-
Octa-
Nona-
Deca-

1
2
3
4
5

6
7
8
9
10

Metals Form Alloys
Metals do not combine with metals. They form
Alloys
which is a solution of a metal in a metal.
Examples are steel, brass, bronze and pewter.

Don't forget the "-ide"!!!
Has a Transition Metal
The metal is NOT a Transition Metal
The metal is NOT a Transition Metal
Calculate the charge of the metal & represent it with a roman numeral.
Name the metal and non-metal and change the ending of the non-metal to "-ide"
Name the metal and the polyatomic ion as given. (Look at chart)
IONIC BOND
Bond formed by the transfer of electrons
A positive charged ion is attracted to a negative charged ion.
Involves a transfer of electrons.
Metals form + ions, nonmetals form – ions, thus an ionic bond forms between a metal and a non-metal.
+ charged ions called cations
- charged ions called anions.

1 V.E. 7 V.E.
8 V.E. 8 V.E.
Ionic bond
– electron from Na is transferred to Cl, this causes a charge imbalance in each atom. The Na becomes (Na+) and the Cl becomes (Cl-), charged particles or ions.

COVALENT BOND
Bond formed by the sharing of electrons
Between nonmetallic elements of similar electronegativity.
Formed by sharing electron pairs
Stable non-ionizing particles, they are not conductors at any state
Examples: O , CO , C H , H O, SiC
NOTE: Bonds in all the polyatomic ions and diatomics are all covalent bonds

2 2 2 6 2
Non-polar
Covalent Bonds
2 Types of Covalent Bonds
Polar
Covalent Bonds
When electrons are shared EQUALLY.
H or Cl
2 2
NO PULL!!!
When electrons are shared but shared UNEQUALLY.
HCl or HF
PULL!!!
E.N. Difference
<0.4
E.N. Difference
0.5 to 2.0
Water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen.
(3.5 - 2.1 = 1.4)
Oxygen has an E.N. of 3.5.
The E.N. difference between two Oxygens is zero. (3.5 - 3.5 = 0)
Metallic Bond
Bond found in metals; holds metal atoms together very strongly
Formed between atoms of metallic elements
Electron cloud around atoms
Good conductors at all states, lustrous, very high melting points
Examples: Na, Fe, Al, Au, Co

Binary Examples:
NaCl
KF
MgCl
MgO
Ca N
2
2
3
Cations
Anions
on the left
on the right
+
-
Polyatomic Examples:
Na SO
KMnO
KNO
Ca(OH)
Li CO
2 4
4
3
2 3
2
1 2 3
1... 2...3!
Three different elements!
Ha ha ha...
Let's Try Bonding Some Elements!!!
Sodium with Chlorine
Sodium with Oxygen
Lithium with Chlorine
Calcium with Chlorine
Calcium with Oxygen
Lithium with Nitrogen
Calcium with Nitrogen
Neutral compounds always have an overall neutral charge.
There are only two different ions in each ionic compound. (one + and one -)
The
positive ion
is ALWAYS listed and named first,
negative ion
second.
Formulas are symbols and subscripts. The subscript tells how many of each atom are in the compound. (NEVER put charges or roman numerals in a formula)

Writing Formulas
Example:
+1

-1
= 0
NaCl

+2

-2
= 0
CaO

+2

-1
= 0
MgCl

+2

-3
=0
Ca N
(x2)
(x3) (x2)
2
3 2
*In Short: Use roman numerals for ALL metals EXCEPT group 1, 2 and Al, Zn, Ag
When do I use Roman Numerals?
Use Roman Numerals for all
Transition Metals
EXCEPT Zn and Ag. (Zn is always +2 & Ag is always +1)
Aluminum (Al) looks like a transition metal but it's charge is always +3.
Tin (Sn)
&
Lead (Pb)
are not
Transition Metals
but they WILL receive a Roman Numeral for their charge.
+1
+1
+1
+1
+1
+1
+2
+2
+2
+2
+2
+2
+3
+2
+1
All other Metals MUST have a Roman Numeral!!!
(All other "pink" elements)
So... Let's say I want to bond Lithium and Sulfur together?
Do I just squish the element symbols together like this:
LiS
NO!!!
The overall charge must equal ZERO!!!
LiS
+1

-2
=
-1
So how can you make it a neutral charge?
Li S
2
+1

-2
= 0
(x2)
Now they're bonded properly...
but wait! There's an easier way...
Criss-Cross Method
Cross the value of the charges to get the appropriate subscripts THEN simplify to lowest whole number ratio.
Li S
+1

-2
Li S
2
Ca S
+2

-2
Ca S
2 2
CaS
REDUCE!!!
We never write a subscript of 1.
NaCl
Na O
LiCl
CaCl
CaO
Li N
Ca N
2
2
3
3 2
NaCl
Na O
LiCl
CaCl
CaO
Li N
Ca N
2
2
3
3 2
Name these Ionic Compounds from earlier.
Sodium Chloride
Sodium Oxide
Lithium Chloride
Calcium Chloride
Calcium Oxide
Lithium Nitride
Calcium Nitride
*Remember the Criss-Cross Method only works with Ionic Compounds.
Drop the sign!!!
Na - sodium ion
Zn - zinc ion
Cu - copper (I) ion
Fe - iron (III) ion
Mn - manganese (VII) ion
Sn - tin (IV) ion
+
+2
+1
+3
+7
+4
No Roman Numeral
Name the metal and non-metal and change the ending of the non-metal to "-ide"
CuBr
NiO
FeN
Cu S

2
2
Copper (II) bromide
Nickel (II) oxide
Iron (III) nitride
Copper (I) sulfide
After the charge of the Transition Metal is identified, then name the anion.
Fe O

FeO

Fe O

FeO
2
2
2 3
?

-2
= 0
(x2)
?

-2
= 0
?

-2
= 0
?

-2
= 0
(x2) (x3)
(x2)
Or
2
x
+ (
-2
) = 0
2
x
=+2
x
=+1
Fe
= +1
Iron (I) oxide
Iron (II) oxide
Iron (III) oxide
Iron (IV) oxide
Or
x
+ (
-2
) = 0
x
=+2
Fe
= +2
Or
2
x
+ 3(
-2
) = 0
2
x
=+6
x
=+3
Fe
= +3
Or
x
+ 2(
-2
) = 0
x
- 4

= 0
x
=+4
Fe
= +4
Name the following Ionic Compounds
THE ROMAN NUMERAL IS NOT THE SUBSCRIPT!!!
Polyatomic ions have given names you must memorize
(see handout)

Na SO
KClO
Ca(CN)
NaOH
Li CO
2 4
2
2 3
Name the following polyatomic compounds:
Sodium sulfate
Potassium hypochlorite
Calcium cyanide
Sodium hydroxide
Lithium carbonate
Fe(CN)
CuOH
Sn(CO )
Au(ClO )
CoSO
Name the following polyatomic compounds:
Iron (II) cyanide
Copper (I) hydroxide
Tin (IV) carbonate
Gold (II) chlorate
Cobalt (II) sulfate
2
3 2
3 2
4
Name the following Covalent Compounds:
The prefix "Mono-" is NOT used on the first element.
NO
N O
CO
CO
H O
C H
2
2
2
2 4
4 8
Nitrogen
di
oxide
Di
nitrogen
tetr
oxide
Carbon
mon
oxide
Carbon
di
oxide
Di
hydrogen
mon
oxide
Tetra
carbon
octa
hydride
Covalent compounds DO NOT use the Criss-Cross Method.
Formula Mass
Formula weight is the sum of the atomic masses.
Example: CO
Mass of C + O + O
12.011 + 15.994 + 15.994
43.999amu

2
Practice
Compute the mass of the following compounds round to nearest hundredth & state type of bond:
NaCl


C H


Fe (CO )
2 6
2 3 3
Please don't...
22.99 + 35.45 = 58.44amu;
Ionic Bond
24.02 + 6.06 = 30.08amu;
Covalent Bond
2(55.85) + 3(12.01 + (3x16.00)) = 291.73amu;
Ionic Bond
Now do them backwards!
Ionic VS Covalent
High melting point.
Low melting point.
High boiling point.
Low boiling point.
Usually crystalline
Solid, liquid or gas.
solid.
Conducts electricity
Poor electrical

when melted.
conductors in all phases.
Mostly soluble in
Mostly insoluble in

water.
water.
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