Post on 18-Jan-2016
IPC 03B Chemical Bonding
Number of Valence ElectronsValence Electrons: Are electrons in the highest
energy level.
The noble gases have 8 electrons.
Gro
up
1 h
as 1
v.e
-
Gro
up
2 h
as 2
v.e
-
Gro
up
13
has
3 v
.e-
Gro
up
17
has
7 v
.e-
Gro
up
18
has
8 v
.e-
Valence electrons are represented using dot diagrams.
Valence electrons (dots) are placed around the four sides of the element symbol.
Electrons (dots) begin to pair up only when no more single spaces are left.
Octet Rule: atoms will gain, lose, or share e- in order to have 8 valence e- and become
stable.
Exception: the first energy level only needs 2 valence electrons to be stable.
So, Helium is stable and will not bond with other atoms.
Stable Atoms
Atoms with less than 8 valence electrons are not very stable.
Atoms with 8 valence electrons are very stable. Helium is stable with two electrons.
Chlorine has 7 valence electrons (not stable).
Chlorine gains an electron to have 8 valence electrons (stable).
Are these elements stable?
A neon atom is stable because it has an octet (8 valence e-).
A sodium atom is unstable because it has only one valence e-.
Stable atoms have full valence shells.
Lithium atoms have 3 e-. Since the 1st energy level only holds 2 e-, lithium has 1 valence e-.
If lithium loses that electron, it will have a full valence shell with 2 e- and an oxidation number of +1.
Li Li +
Net Ionic Charges
Metals will lose electrons to form positive ions.
Nonmetals will gain electrons to form negative ions.
Groups/Families
Group Number Group Name Valence Electrons Oxidation Number
1 Alkali Metals 1 +1
2 Alkaline Metals 2 +2
3-12 Transition Metals 2 Vary
13 Boron Family 3 +3
14 Carbon Family 4 +/4
15 Nitrogen Family 5 3
16 Oxygen Family 6 2
17 Halogens 7 1
18 Noble Gases 8 0
Chemical Bonds
Compounds are made up of more than one atom.
When atoms combine to make molecules, they form chemical bonds.
Types of Bonds:Ionic BondsCovalent BondsMetallic Bonds
Ionic Bonding
Ions: atoms with a positive (+) or negative (-) charge.
Metals tend to lose electrons to form positive ions called cations.
Chloride ion
Sodium ion
• Nonmetals tend to gain electrons to form negative ions called anions.
Bond Formation:
opposite charges attract
electrons are transferred from a metal atom to a nonmetal atom
+11-11
+11-10
+17-17
+17-18
Oxidation Numbers
No
Ion
s!
-1
Write the charges on your periodic table!
6 Steps to Writing Ionic Compounds
1. Identify the (+) ion and the () ion.
2. Write the symbols with their charges.
3. Cross the charges.
4. Remove the charges.
5. Simplify the numbers.
6. Remove the “1”s and write the formula.
1. Magnesium Sulfide
2. Mg+2 S-2
3. Mg-2 S+2
4. Mg2 S2
5. Mg1 S1
6. MgS
______________(+) ion
_________() ion
see periodic table
Both #’s are divisible by
2.
Metal first; then
nonmetal.
Tutorial
Practice Steps
Sodium Chloride
Aluminum Sulfide
1. Identify the (+) ion and the () ion.
2. Write the symbols with their charges.
3. Cross the charges.
4. Remove the charges.
5. Simplify the numbers.
6. Remove the “1”s and write the formula.
Na+1 Cl-1
__________(+) ion
__________() ion
Na-1 Cl+1 Na1Cl1
NaCl
Al+3 S-2Al-2 S+3 Al2S3
Al2S3
_____________(+) ion
__________() ion
Reason: Total Charges = ZeroAluminum Sulfide
Al3+ S2-
S2-Al3+
S2-
Need 2 Al+3 ions
Al2S3
+6 + -6 = 0
Al+3 S-2
-2 +3Need 3 S-2 Ions
Polyatomic Ions (EOC)
Combining Atoms
Positive ions must cancel the negative ions to make a neutral molecule.
Ca2+
-1
-1
Ca(OH)2
If you need more than one polyatomic ion, use ( ).
Aluminum Sulfate
Al3+
Al3+
Need 2 Al+3 ions
Al2(SO4)3
+6 + -6 = 0
Al+3 (SO4)-2
-2 +3Need 3 SO4
-2 Ions
Put ( )’s around the polyatomic ions so you don’t get the numbers confused.
Properties of Ionic Compounds (Salts)
solid, crystalline structure
high melting point
Made up of metal w/ nonmetal
hard or brittle (not malleable)
conduct electricity when melted or dissolved
nonconductor as a solid
Some soluble in water
Covalent Bonding in Action
Covalent Bonding
•Covalent Bond: Shared pair of electrons between two nonmetals.•Covalent compounds are called molecular compounds.
Atoms share electrons in order to get 8 valence electrons. (Remember the Octet Rule) (Exception: only 2 e- for H)
Diatomic Elements7- Up
Diatomic means “2 atoms” These 7 elements exist in
nature as diatomic molecules (covalently bond).
H2 (g) O2 (g) F2 (g) Br2 (l) I2 (s) N2 (g) Cl2 (g)
“HOFBrINCl”
Greek Prefixes
Prefix Meaning
Mono- 1
Di- 2
Tri- 3
Tetra- 4
Penta- 5
Hexa- 6
Hepta- 7
Octa- 8
Nona- 9
Deca- 10
Don’t use prefix “mono” on the first element, only on the second.
Certain vowel combinations are not allowed: oo and aoEx. Don’t write tetraoxide; do write tetroxide.
Naming Molecular Compounds
1) First Nonmetal: (Greek prefix + element name)
2) Second Nonmetal: (Greek prefix + element root + -ide ending)
Practice:
1. CCl4
2. SO3
3. N2O
4. P2O5
5. CO2
6. SF6
Carbon Tetrachloride
Sulfur Trioxide
Dinitrogen monoxide
Diphosphorous pentoxide
Carbon Dioxide
Sulfur Hexafluoride
Writing Molecular Compounds
1) nonmetal with nonmetal: Write the element symbol followed by the Greek prefix as a subscript for both elements.
Practice:
1. Dinitrogen tetroxide
2. Carbon monoxide
3. Sulfur dioxide
4. Phosphorus pentachloride
N2O4
CO
SO2
PCl5
Type of Chemical Bond
Ionic Bonds have ions!Metal & NonmetalPolyatomic ion & NonmetalPolyatomic ion & Polyatomic ionAttraction between pos. & neg. ions
Covalent Bonds have nonmetals!Nonmetal & NonmetalSharing of electrons
Metallic Bonds (free e-)
Metallic BondThe metal is held together by the strong forces of attraction between the positive nuclei of the metallic cation and the “free floating” valence electrons known as a “Sea of Electrons”.
Sea of Electrons