Chemistry Unit 2
(2013-2014)
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What is an ion?
Define ionic bond.
Define covalent bond.
Define valence electrons
Define Chemical Compound
Define binary compound (ionic or molecular)
Define ternary compound
Compound
• Are formed when two or more atoms join
together
• All molecules of a chemical compound have the
same types and number of atoms
• Why do atoms combine?
– To become stable (to fill outer electron shell)
• How do atoms combine?
– By gaining or losing electrons
– By sharing electrons
– By metallic bonding
Types of Compounds
• Binary ionic compound : two different elements, one is
metal the other is nonmetal.
KCl, NaCl,
• Binary molecular compound: two elements both are
nonmetals
Ex. H2O or NH3,
H2 is a molecular compound but it is not a binary
molecular compound
• Ternary ionic compound: three different elements, one
is metal the others are nonmetals.
KNO3 , Al(NO3)3 , C6H12O6
CHEMICAL BONDS
Page 602-614
A) IONIC BONDS:
- chemical bond between metal & non-metal
- electrons transfer takes place
B) COVALENT BONDS:
- chemical bond between two non-metals
- electron sharing takes place
C) METALLIC BONDS
- chemical bond between two metals
- positive charged metal ions are surrounded by cloud
of electrons. This is why metals are conductors. Pg.571
Intramolecular bonds
a) Ionic bonding: transfer of electron. It
occurs between metal and non metal.
Metal gives electron, non-metal takes
electron.
Why?
Ionic bond
Intramolecular bonds
b) Covalent bonding
Atoms share the electron
pairs.
It occurs between two
non-metals
Formation of covalent bond
METALLIC BOND
METALLIC BOND
• Monoatomic ion: It has only one atom
• Ex. Na1+
Cl1-
• Polyatomic ion: it has more than one atom
• Ex. NH4+
CO32-
Monoatomic ions
Monoatomic and polyatomic positive
ions
Monoatomic and polyatomic negative
ions
Oxidation number
• An oxidation number tells us how many
electrons an atom has gained, lost or shared
to become stable.
For ionic compound the oxidation number is the
same as the charge on the ion.
• Ex. Na has 1+ its oxidation number is 1+
• Cl has 1- so its oxidation number is 1-
What is the oxidation number of Fe in the
compound Fe2S3 ?
What is the oxidation number of Cu in the
compound CuO ?
Writing Formulas
1- Write the symbol of the element or polyatomic ion that has
the positive charge. (Hydrogen, ammonium, NH+ and all
metals have positive charge)
2- Write the symbol of the element or polyatomic ion that has
the negative charge. (Nonmetals other than hydrogen and
polyatomic ions other than NH4+ Have negative charge)
3- The charge (without the sign) of one ion becomes the
subscript of the other ion.
What is the chemical formula for lead (II) oxide?
What is the name of KOH?
• What is the formula for lithium nitride
• Li1+
N3• Li1+ + N3-
Li3N1
or
Li3N
• What is the formula for calcium chloride?
Writing names
(ionic compounds)
1- Write the names of the positive ion.
2- Using the Table 2, check to see if the positive ion is capable of
forming more than one oxidation number. If it is, determine the
oxidation number of the ion from the formula of the compound.
Overall charge is zero and the negative ion has only one possible
charge. Write the the charge of the positive ion using roman
numerals in parentheses after the ion’s name.
3- Write the root name of the negative ion. The root name is the first
part of the element’s name. Ex. Chlorine chlor-, oxygen ox4- Add the ending –ide to the root.
Ex. BaF2 is named barium fluoride
Writing names
(molecular compounds)
• Write the name of the first element. If its
subscript is more than one add appropriate
Greek prefix to the name.
• Write the root name of the second element
with the –ide ending. If its subscript is more
than one add appropriate Greek prefix to the
name.
• Ex. NO, NO2, N2O, N2O5
Chemical equations
• Why do scientists use chemical equations?
It is easier to write/shorter than the words
It gives the states (gas, liquid, solid) of the
matter
What are the reactants? What are the products?
C6H12O6 + 6O2 ---------- 6CO2 + 6H2O
• What information does this chemical equation
give you?
Zn(s) + 2HCl(aq)
H2 (g) + ZnCl2 (aq)
States of matter for each substances involved.
How much of each atom and each substances
What is the law of conservation mass?
• The mass of the reactants must equal the
mass of the products, mass is not created or
destroyed.
Zn(s) + 2HCl(aq)
H2 (g) + ZnCl2 (aq)
In the equation above, how much H2 gas was produced if 22 g of
Zn reacts with 15 g of HCl and 28 g of ZnCl2 remains?
Zn(s) + 2HCl(aq)
22 g
28 g
15 g
Reactants: 22+15=37
Products: 22+?=37
?= 37-28= 9 g
H2 (g) + ZnCl2 (aq)
?g
Coefficient and Subscripts
• Coefficients represent the number of units of each
substance taking part in a reaction.
4NO2 coefficient number of NO2 is 4, means there are
4 NO2 molecule.
• Subscript: is a digit in a chemical formula that
represents the number of atoms or ions occurring in
the substance.
Ex: NO2 subscript of oxygen is 2, means there are two
oxygen atom in the compound.
Balancing a Reaction
1- Write a chemical equation for the reaction
2- Count the atoms in the reactants and the
products.
3- Chose coefficients that will bring the equation
closer to balanced.
4- Recheck the numbers of each atom on each
side of the equation.
5- Repeat steps 3 and 4 until the equation is
balanced.
Balancing a Reaction
• HgO(s)
Atoms
Hg (l) + O2
HgO(s)
Hg (l) + O2
Hg
1
1
O
1
2
Which coefficient can we use to balance it?
Can we change subscripts? NO
Atoms
2HgO(s)
2Hg (l) + O2
Balance the following equations.
1- Mg(s) + O2
MgO
2- Li(s) + H2O
LiOH + H2
Why do the equations need to be
balanced?
• Because of the law of conservation of mass
which states that;
the mass of the reactants must be = the mass of the product