Download The valency

Chemical compounds
lesson-2 unit-1
Made by:
Dr. Niveen Fawzy
The valency
• During chemical reactions atoms try to reach
the stable state by:
-Loosing their outermost electrons (in case of metals)
-Gaining a no. of electrons to complete the outer shell
by (8) electrons (in case of non-metals)
-Sharing a no. of electrons with other atoms (in case
of non-metals)
• The valency:
• It’s the no. of electrons that an atom gains or loses or
shares during a chemical reaction
• N.B: The outermost electrons of an atom determines
its valency
Element
Atomic
no.
Electronic
During
configuration
chemical
K
L M
N reaction
Formed Valency
ion
11
2
8
1
-
Loses one
electron
Monovalent
17
2
8
7
-
Gains or shares
with one electron
Monovalent
8
2
6
-
-
Gains or shares
with 2 electrons
Divalent
12
2
8
2
- Loses 2
electrons
Divalent
13
2
8
3
- Loses 3
Trivalent
Some metals & their valencies
Metal
Valency
Metal
Valency
Metal
Valency
Lithium (Li)
Monovalent
Calcium (Ca)
Divalent
Aluminum (Al)
Trivalent
Potassium (K)
Monovalent
Magnesium
(Mg)
Divalent
Gold ( Au)
Trivalent
Sodium (Na)
Monovalent
Iron II
Divalent
Iron III ( Fe)
Trivalent
Silver (Ag)
Monovalent
Lead ( Pb)
Divalent
Copper I (Cu)
Monovalent
Copper II
(Cu)
Divalent
Mercury (Hg)
Divalent
(Fe)
Some metallic elements have more than one
valency such as:
Copper I Monovalent
Copper II Divalent
Iron I Monovalent
Iron II Divalent
• Some non-metals & their valencies:
Non-metals
Valency
Non-metal
valency
Hydrogen (H)
Monovalent
Sulphur (S)
Tetravalent
Chlorine (Cl)
Monovalent
Carbon (C)
Tetravalent
Fluorine (F)
Monovalent
Nitrogen (N)
Pentavalent
Bromine (Br)
Monovalent
Phosphorus (P)
Pentavalent
Iodine (I)
Monovalent
Sulphur (S)
Hexavalent
Sulphur (S)
Divalent
Oxygen (O)
Divalent
Nitrogen (N)
Trivalent
Phosphorus (P)
Trivalent
Give reason:
Atomic group (Radical)
• Its properties: It’s a set of atoms of different
elements joined together , behave like one atom
during a chemical reaction , having its own valency
& doesn’t exist solely
Atomic
group
valency Atomic
group
valency Atomic
group
valency
Monovalent
Divalent
Trivalent
Monovalent
Divalent
Monovalent
Monovalent
Monovalent
Chemical formula
• It’s a formula that represents the number & types of
atoms in a molecule
• Steps to write a chemical formula for a compound:
Steps
1- Write name of compound with
words
2- Write symbol of element or atomic
group
3- Write valency under each symbol
4- Exchange their valencies & simplify
them
5- We don’t write the valency if it
equals one
Examples
Write the chemical formula of:
•
•
•
•
Write the chemical formula of the following &
no. of elements & no. of atoms of each
1- Aluminum carbonate
2- Copper carbonate
3- Sodium nitrate
4- Calcium sulphate
5- Hydrogen chloride
Types of compounds
• Compounds can be classified acc. to their properties into:
1- Acids
2- Bases
3 -Oxides
4- Salts
First: Acids & Bases (alkalis)
Acids
Bases (alkalis)
Notice that:
Classification of acids
• Acids are classified acc. to their strength(degree of
Ionization):
Strong acids
Weak acids
Acids are classified acc. To their stability (Bp &
difficulty of its decomposition):
Stable acids
Unstable acids
Sulphuric acid is the most
stable acid due to its high
boiling point
Carbonic acid
• Warning:
• Never touch acids or bases with bare hands as they
have corrosive effect on skin
• Sodium hydroxide is also called (caustic soda)
• Calcium hydroxide is also called (lime water)
• If we have 2 test tubes , one containing acid & the
other base we can distinguish them by using litmus
paper
Oxides & its classification
• They are compounds resulted from combination
between oxygen& an element (metal & non-metal)
Metal oxides
Non-metal oxides
Salts
• They are compounds resulted from the combination of a
positive ion or ( positive atomic group) with a negative atomic
group or ( a negative non-metal ion except oxygen)
• Formation of salts
Positive ion
with negative
ion
Positive ion
with negative
atomic group
Positive
atomic group
with negative
ion
Positive
atomic group
with negative
atomic group
Classification of mineral salts
Salts dissolved
(soluble) in water
Salts undissolved
(insoluble) in water
NB.
-Salts exists in earth crust or is dissolved in
water
-They are variant in taste ,color ,smell , solubility
in water
Model answers of book pages
25,26
•
•
•
•
Question (2):
(A):
Answer in slide no. 11
(B): Give reason:
• 1- Because acids produce positive hydrogen ions ,
while bases produce negative hydroxide ions
• 2- Because during chemical reactions potassium
atom loses one electron , while oxygen atom gains
or shares with 2 electrons
• 3- Because oxygen is divalent , while sodium is
monovalent