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 configuration K L M N During chemical reaction Formed ion Valency Loses one electron Monovalent Gains or shares with one electron Monovalent Gains or shares with 2 electrons Divalent Loses 2 electrons Divalent Loses 3 electrons Trivalent

Some metals & their valencies MetalValency MetalValency MetalValency Lithium (Li)MonovalentCalcium (Ca)DivalentAluminum (Al)Trivalent Potassium (K)MonovalentMagnesium (Mg) DivalentGold ( Au)Trivalent Sodium (Na)MonovalentIron II (Fe)DivalentIron III ( Fe)Trivalent Silver (Ag)MonovalentLead ( Pb)Divalent Copper I (Cu)MonovalentCopper 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)MonovalentSulphur (S)Tetravalent Chlorine (Cl)MonovalentCarbon (C)Tetravalent Fluorine (F)MonovalentNitrogen (N)Pentavalent Bromine (Br)MonovalentPhosphorus (P)Pentavalent Iodine (I)MonovalentSulphur (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 valencyAtomic group valencyAtomic group valency Monovalent DivalentTrivalent Monovalent Divalent 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: StepsExamples 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

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 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) Metal oxidesNon-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