0Atoms combine with each other to form various compounds. The smallest unit of a substance which can exist independently is called a molecule. So, atoms combine with each other to form molecules. These molecules can be formed through either ionic, metallic, covalent or hydrogen bonding.
The chemical behavior of any element depends upon the position of the element in the periodic table. The position of an element in the periodic table is related to its electronic configuration. So, the chemical reactivity of an element depends upon its electronics configuration, i.e., the chemical reactivity of an element depends upon the distribution of electrons in its atom.It has been found that the atoms having a total of 2,10,18,36,54, and 86 electrons are the most stable, i.e., such atoms do not show any chemical reactivity. These electrons configurations are those of the noble gasses, viz., Helium, Neon, Argon, Krypton, xenon, and Radon, respectively. These elements called noble gasses do not form compounds either among themselves or with other elements. Xenon, however, forms fluorides and oxyfluoride under controlled conditions. This non-reactivity of noble gasses is due to their stable electronic configurations.All other elements having less than eight electrons in their outermost shell (except helium which has been two electrons in its outermost shell) show a reasonable chemical activity.
IONIC BONDING
Ionic bonding occurs when atoms either gain or lose one or more valence electrons, resulting in the atom having either a negative or positive charge.
COVALENT BONDING
Instead of losing or gaining electrons, some atoms instead share electrons when they form molecules. Atoms that form bonds by this method, called covalent bonding, are usually non-metals. By sharing electrons, the resulting molecules are more stable than their previous components were, since this bond allows each atom to fulfill its electron requirements; that is, the electrons are attracted to the nuclei of each atom. Atoms of the same element can form single, double or triple covalent bonds, depending on the number of valence electrons they contain.
METALLIC BONDING
This type of bond occurs between metals. In metallic bonding, many atoms share valence electrons; this occurs because individual atoms only loosely hold their electrons. It is this ability of electrons to move freely between numerous atoms that give metals their distinctive qualities, such as malleability and conductivity. This ability to bend or be shaped without breaking occurs because the electrons simply slide over each other instead of separating. The ability for metals to conduct electricity also occurs because these shared electrons readily pass between atoms.
HYDROGEN BONDING
While ionic, covalent and metallic bonding is the main types of bonding used to form compounds and give them their unique qualities, hydrogen bonding is a very specialized type of bonding that only occurs between hydrogen and oxygen, nitrogen or fluorine. Since these atoms are much larger than a hydrogen atom, the electrons will tend to stay closer to the larger atom, giving it a slightly negative charge and the hydrogen atom a slightly positive charge. It is this polarity that allows water molecules to stick together; this polarity also allows water to dissolve many other compounds.
