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INTRODUCTION
Only a few elements, particularly the noble gases, exist as individual atoms. Most atoms are joined by chemical bonds to other atoms.
Chemical bonds are forces that hold the atoms together in a molecule. They are a result of strong intramolecular interactions among the atoms of a molecule. The valence (outermost) electrons of the atoms participate in chemical bonds.
When two atoms approach each other, these outer electrons start to interact. Although electrons repel each other, they are attracted to the protons within atoms. The interplay of forces results in the formation of bonds between the atoms. The main types of chemical bonds are ionic bond, covalent bond, hydrogen bond, and metallic bond .
A bond between two atoms depends upon the electronegativity difference between the atoms. If the electronegativity difference is significantly high, the atoms transfer electrons to form ions and thereby form an ionic bond. If the electronegativity difference is zero or small, then the atoms combine to form covalent bonds.
Elemental hydrogen exists as molecules, each consisting of 2H atoms linked by a chemical bond. Because hydrogen molecules contain 2H atoms, they are said to be diatomic and are denoted by the chemical formula H2. The H atoms in the H2 molecule are held together by a covalent bond made up of 2electrons, each contributed by one of the H atoms, and shared between the atoms.