WBCS Preliminary (Chemistry): Chemical Bonding

• Atoms are made up of three smaller particles called protons, neutrons and electrons. The protons and neutrons are found in the nucleus of the atom. Protons have a single positive charge. This is called the Atomic Number of an atom. The Atomic Number tells us the number of electrons that the atom contains. It is these electrons that determine the chemical properties of the atom and the way it combines with other atoms to form specific compounds. Electrons have a single negative charge. Normally, atoms are electrically neutral so that the number of electrons is equal to the number of protons.
• Electrons orbit around the nucleus. Electrons cannot orbit the nucleus of an atom in any orbit. The electrons are restricted to specific paths called orbitals or shells. Each shell can only hold a certain number of electrons. When a shell is full, no more electrons can go into that shell. The key to the properties of atoms is the electrons in the outer shell. A complete outer shell of electrons is a very stable condition for an atom.
• Valency: Hydrogen is the simplest element. It has one electron. Its outer shell only holds two electrons. Valency can be simply defined as the number of Hydrogen atoms that an element can combine with. The atoms with full electron shells (Helium, Neon, Argon) are chemically inert forming few compounds. The atoms don't even interact with each other very much. These elements are gases with very low boiling points. The atoms with a single outer electron or a single missing electron are all highly reactive. Sodium is more reactive than Magnesium. Chlorine is more reactive than Oxygen. Generally speaking, the closer an atom is to having a full electron shell, the more reactive it is. Atoms with one outer electron are more reactive than those with two outer electrons, etc. Atoms that are one electron short of a full shell are more reactive than those that are two short.
• Chemical bonds are what hold atoms together to form the more complicated aggregates that we know as molecules and extended solids. The forces that hold bonded atoms together are basically just the same kinds of electrostatic attractions that bind the electrons of an atom to its positively-charged nucleus. chemical bonding occurs when one or more electrons are simultaneously attracted to two nuclei. .
• Mainly 3 Types of bonds can be present in Chemical Compounds.
  1. Electrovalent or Ionic Bond: It is formed by Transferring of Electrons between 2 Atoms. These types of bonds are mainly formed between Metals and Non - Metals. These compounds exist in solid form. These compounds have high boiling Point, Melting Point and thermal stability.
  2. Covalent Bond: It is formed by equal sharing of Electrons between 2 Atoms. This type of bond is mainly formed between non - metals. These compounds may be solid, liquid or gas. These compounds have low boiling Point, Melting Point and thermal stability in comparison to Ionic Bond.
  3. Co - Ordinate or Dative Bond : It is formed by unequal sharing of Electrons between 2 Atoms. This bond is also called as Semi - Polar bond since; it involves Electrovalency and Covalency both. These compounds may be solid, liquid or gas. These compounds are insoluble in H2O. These compounds do not conduct Electricity. These compounds have high B.P. than Covalent Compounds but less than Electrovalent Compounds.