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Sunday, January 19, 2014

Definition of a Molecule and mole

Definition of a Molecule

Molecules are formed when two or more atoms are held together by chemical bonds.

Molecules Formed by Covalent Bonds

For example, the oxygen molecule consists of two atoms of oxygen. In the case of oxygen, the bond that holds the two atoms together is known as a covalent bond, and here is how it works.
The oxygen atom has 8 each of protons, neutrons, and electrons. The protons and neutrons are found in the center of the atom, known as the nucleus, and the electrons surround the nucleus in layers, or shells. The oxygen atom has 2 electrons in its first shell, and 6 in its second and outer shell. However, in chemistry, there exists the octet rule, which states that atoms generally strive to have 8 electrons in their outer shell. The oxygen therefore is 2 electrons away from a complete outer shell. When it binds with another oxygen atom, they can share two pairs of electrons and so each will have 8. When atoms share electrons like that, they form a molecule through a covalent bond.

Molecules Formed by Ionic Bonds

Molecules can also be formed through other kinds of chemical bonds, for example, an ionic bond. An example this is sodium chloride, or table salt. In an ionic bond, one atom has a much greater ability to attract electrons than the other atom. In this case, the chlorine, which is only 1 electron short of a complete outer shell, will steal that electron from the sodium, which has only 1 outermost electron. This turns the sodium into a positively charged ion, and the chlorine into a negatively charged ion, and the two atoms end up being held together by an electrostatic charge.

Meaning of a Mole

Now what is a mole? A mole is simply a counting number, much like a dozen. When we say "dozen", we mean 12; well, when we say "a mole" we mean 6.022 x 10 to the 23. Moles make it easier to quantify chemical substances. The periodic table lists the weights of all the elements in grams per mole.

Examples of Finding Molar Mass

For example, oxygen has molar mass of 16, which means 6.022 x 10 to the 23 atoms of oxygen weigh 16 grams. Hydrogen has a molar mass of 1. To find out the molar mass of a molecule, such as water, we need to add up the molar masses of the atoms it is composed of. Since water has two atoms of hydrogen and 1 atom of oxygen, its molar mass is 18 grams per mole.

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