Chemistry

• Chemical bond


  Mutual electrical attraction between the nuclei and valence electrons of different atoms that bind the atoms together
• Chemical bonding


  • Atoms form compounds by gaining, losing or sharing electrons
• Types of bonding


  • Ionic or electrovalent bond
  • Covalent bond
• Ionic or electrovalent bond

  1. Metals lose valence electrons

  2. Non-metals gain valence electrons

  3. Forming balanced electron configuration
• Ionic compounds


  • Sodium chloride crystal
  • Magnesium fluoride
• Ionic radius


  Distance between the centre of the ions
• Covalent bond


  Sharing of electron pairs
• Covalent compounds


  • CO₂
  • CH₄
  • H₂O
  • H₂C=CH₂
• Properties of ionic and covalent bonds

  • Ionic bonding: Combination of metals and non-metals, Metals form positive ions, Non-metals form negative ions, High melting and boiling points, Electrolytes
  • Covalent bonding: Combination of non-metals, Maximum number of bonds equals number of electrons in outer shell, Individual molecules, Molecular structure, Macromolecular structure, Low melting and boiling points, Non-electrolytes, Soluble in organic solvents, Insoluble in water
• Acids have a pH less than 7, while bases have a pH greater than 7.
• A solution with a pH of 7 is neutral (pure water).
• Acid

  A substance which dissolves in water producing H+ as the only positive ion. An acid is a hydrogen ion(proton) donor
• Classes of acids

  • Organic acids
  • Inorganic acids
• Dilute acid

  Acid produced when a large amount of water is added to a small amount of acid
• Concentrated acid

  Acid produced when only a little amount of water is added to a relatively large amount of acid
• Strong acid

  Acid which ionize completely in aqueous solution and have a high concentration of H+
• Strong acids

  • HCl
  • H2SO4
  • HNO3
• Weak acid

  Acid which ionize or dissociate partially(slightly) in aqueous solution and have low concentration of hydrogen ions
• Basicity of an acid

  The number of replaceable hydrogen ions,H+ in molecule of an acid
• Physical properties of acids

  • Sour taste
  • Turn blue litmus paper red
  • Corrosive in nature especially strong acid
• Reaction of acid with metals

  Acid reacts with some metals to liberate hydrogen gas
• Reaction of acids with Base and Alkalis

  Dilute acids react with bases and alkalis to form salts and water (known as NEUTRALIZATION REACTION)
• Reaction of acids with Trioxocarbonate (iv) and hydrogen trioxocarbonate (iv)

  Acid reacts with CO32-or HCO3- to liberate carbon (iv) oxide (CO2)
• Methods of preparing acids

  • Dissolving an acid anhydride in water
  • Combination of constituent elements
  • Heating Hydrogen gas and bromine vapour
  • Displacement of weak or volatile acid from its salt by a strong acid
• Uses of acids

  • Hydrochloric acid
  • Tetraoxosulphate (vi) acid
  • Trioxonitrate (v) acid
  • Acetic acid (ethanoic)
  • Tartaric
  • Citric acid
  • Fatty acids
• Neutralization is the reaction of an acid with a base to form a salt and water
• Chemical properties of acids

  • Reaction of acid with metals
  • Reaction of acids with Base and Alkalis
  • Reaction of acids with Trioxocarbonate (iv) and hydrogen trioxocarbonate (iv)
• Base

  A substance which will neutralize an acid to yield salt and water only. It is either an oxide or hydroxide of a metal
• Alkali

  A basic hydroxide which is soluble in water
• Strength of an alkali

  The degree of its ionization in water
• Strong alkalis

  • Potassium hydroxide, sodium hydroxide, calcium hydroxide, strontium hydroxide
• Weak alkali

  • Aqueous ammonia
• Physical properties of bases

  • Soapy to touch
  • Bitter taste
  • Turn red litmus blue
  • Concentrated form are corrosive
  • Electrolytes
• Methods of preparing bases

  • Combustion of a reactive metal in air
  • Reaction of metals with water (steam)
  • Decomposition of metal hydroxides by heating
  • Precipitation or double decomposition reaction
  • Dissolution of metallic oxides in water
• Reaction of metallic hydroxide with heat

  Metallic hydroxide decomposes to form metal oxide and water
• Reaction of alkali with ammonium salts

  Alkali reacts with ammonium salts in the presence of heat to liberate ammonia gas
• Uses of bases

  • NaOH as drying agent
  • Making soap
  • Neutralizing soil acidity
  • Toothpaste production
  • Making mortar, plaster of Paris, white wash and cement
  • Sugar refining
  • NH4OH as cleanser and grease solvent
  • NH3 in making fertilizers and detergents
• pH

  Hydrogen ion index, a number-scale used to express the degree of acidity or alkalinity of a solution
• pH scale

  • 1-3 (Very acidic)
  • 4-5 (Weak acid)
  • 6 (Very weak acid)
  • 7 (Neutral)
  • 8 (Very weak base)
  • 9-10 (Weak base)
  • 11-14 (Very basic)
• Logarithmic pH scale

  Introduced by Sorensen in 1909 to eliminate the inconvenience encountered when using negative indices and to give room for wide range of [H+]and [OH-] concentrations