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

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 (Fe) Divalent Iron III ( Fe) Trivalent

Silver (Ag) Monovalent Lead ( Pb) Divalent

Copper I (Cu) Monovalent Copper II (Cu)

Divalent

Mercury (Hg) Divalent

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

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:

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)

Notice that:

Classification of acids• Acids are classified acc. to their strength(degree of

Ionization):

Stable acids Unstable acids

Sulphuric acid is the most stable acid due to its high boiling point

Carbonic acid

Acids are classified acc. To their stability (Bp & difficulty of its decomposition):

• 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)

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

Classification of mineral salts

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