Molecules

Molecules are group of two or more atoms held together by chemical bond. For example, two
hydrogen atoms and an oxygen atom are bound together to form water molecule. Trillions of
water molecules come together to form a water droplet. Not all molecules are as simple as
water molecules. For example, a DNA molecule that holds the code of life is a highly complex
molecule. As mentioned in Introduction to Biology subatomic particles come together to form
atoms, atoms combine to form molecules, molecules combine to form organelles, organelles
combine to form cells, cells combine to form tissues, tissues combine to form organs and so on.

There are two ways in which atoms can combine to form larger particles. One way is to fuse the
nuclei of atoms in what is known as fusion reaction. The product of such fusion reaction is the
formation of new elements. The other way is for atoms to share their electrons with other atoms
in what is called chemical reactions. The product of such reaction is the formation of molecules.