The three isotopes of carbon are ₆¹²C, ₆¹³C, ₆¹⁴C. Since  the isotopes of an element contain the same number of electrons, they have identical electronic configuration. Thus, all the isotopes of an element show identical chemical properties. Since the masses of the isotopes of an element are slightly different, therefore, their physical properties (like density, melting point, boiling point, etc.) are slightly different.

Radioactive isotopes

Some isotopes are unstable due to the presence of extra neutrons in their nuclei. The isotopes which are unstable and emit various types of radiations are called radioactive isotopes. The radiations are emitted in the form  of  alpha particles, beta  particles and gamma rays. Example of radioactive isotopes: Carbon-14, Sodium-24, Cabalt-60, Arsenic-74, Iodine-131, and Uranium-235.They emit  high energy radiations which are harmful to human beings. Therefore, these radioactive isotopes should be used very carefully.

Applications of Radioactive Isotopes

• They are used as fuel in nuclear reactors of nuclear power plants for generating electricity. Uranium-235 is used for this purpose. Radioactive isotopes like Uranium-235 and Plutonium-239 are also used for making nuclear bombs.
• They are used in medicine to detect the presence of tumors and blood clots in the body. A small amount of the radioactive compound (called tracer) is either injected into the body or is given orally. It accumulates in the area of the tumor or blood clot. The extra position of the accumulated tracer can be determined with the help of the instrument, the Geiger Counter. Arsenic-74 is used to detect the presence of tumors and Sodium-24 is used for blood clots.
• They are used in the treatment of cancer (radiotherapy). High energy gamma radiations emitted by Cobalt-60 are used to bum cancerous cells.
• They are used to determine the activity of the thyroid gland. This helps in the treatment of diseases like goitre.
• They are used to detect leakages in underground oil pipelines, gas pipelines and water pipes. A solution of the radioactive substance is introduced in the pipeline.

This solution leaks out from any crack that might be present and is detected with the help of the Geiger Counter.

Isobars

Atoms of different elements having different atomic numbers but same mass number (atomic mass) are called isobars. Isobars have different number of protons but the total of the protons and neutrons in their nuclei is the same. For example , Argon (₁₈⁴⁰Ar)  and Calcium (₂₀⁴⁰Ca) are isobars.

Ions

A positively or negatively charged atom (or group of atoms), formed by the loss or gain of electrons by the atom, is known as an ion. Ions contain an unequal number of electrons and protons and are of two types:

• Cation: A positively charged ion is known as a cation. It is formed by the loss of one or more electrons by an atom. Example: Sodium ion, Na⁺, Calcium ion, Ca²⁺, Aluminum ion, Al³⁺. All metal atoms form cations as they can lose electrons easily Lithium ion batteries are used in mobile phones.
• Anion: A negatively charged ion is known as an anion. It is formed by the gain of one or more electrons by an atom. Example: Chloride ion, Cl^-, and Oxide ion, O^2-. The ions of all non-metals are anions (except hydrogen ion and ammonium ion, which are cations).

Some if the common ions are given in the table below.

Ionic Compounds

The compound which are made up of ions are called Ionic compounds. Sodium chloride (common salt), copper sulphate, and potassium nitrate are examples of ionic compounds. These compounds are formed by the combination between metals and non-metals.

The valency of an ion is equal to the charge on the ion. While writing the formula of an ionic compound, the number of cations and anions is adjusted so that the total number of positive charges is equal to the total number of negative charges. Thus the formula for Magnesium chloride is MgCl₂. From the above table since Mg ion has charge +2 and Cl ion has charge -1 two Cl ions are needed with one Mg ion, thus giving it the formula MgCl₂.

Gram Atomic Mass and Gram Molecular Mass

The amount of a substance for which mass in grams is numerically equal to its atomic mass is called gram atomic mass of that substance. For example, the atomic mass of carbon is 12u, so its gram atomic mass is 12 grams. The gram atomic mass of a substance represents the mass of 1  mole  of atom (6.023 x 10²³ atoms) of that substance.

The molar mass of a substance is the mass of 1 mole of that substance. The unit of molar mass is grams per mole. The molar mass of an element has 6.023 x 10²³ atoms of the element in it. The molar mass of an element is equal to the gram atomic mass of the element expressed in g/mol.

The amount of a substance whose mass in grams is numerically equal to its molecular mass is called gram molecular mass of that substance. The molecular mass of water (H₂O) is 18u, so its gram molecular mass is 18 grams. The gram molecular mass of a substance represents the mass of 1 mole of molecules (6.023 x 10²³ molecules) of that substance.

The mole concept

 Mole is a link between the mass of atoms (or molecules) and the number of atoms (or molecules). A group of 6.023 x 10²³ particles (atoms or molecules) of a substance is called a mole of that substance.

For examples,

• 1mole of nitrogen atoms (N) = 6.023 x 10²³ nitrogen atoms.
• 1mole of nitrogen molecules (N₂) = 6.023 x 10²³ nitrogen molecules
• The number, 6.023 x 10²³, which represents a mole, is known as Avogadro's Number.
• Number of moles of atoms = Mass of element in grams/ Gram atomic mass of element (or molar mass of element)
• Number of moles of molecules = Mass of substance in grams/ Gram molecular mass of substance (or molar mass of substance)

Ionic Compounds

The compound which are made up of ions are called Ionic compounds. Sodium chloride (common salt), copper sulphate, and potassium nitrate are examples of ionic compounds. These compounds are formed by the combination between metals and non-metals.

The valency of an ion is equal to the charge on the ion. While writing the formula of an ionic compound, the number of cations and anions is adjusted so that the total number of positive charges is equal to the total number of negative charges. Thus the formula for Magnesium chloride is MgCl2. From the above table since Mg ion has charge +2 and Cl ion has charge -1 two Cl ions are needed with one Mg ion, thus giving it the formula MgCl₂.

Gram Atomic Mass and Gram Molecular Mass

The amount of a substance for which mass in grams is numerically equal to its atomic mass is called gram atomic mass of that substance. For example, the atomic mass of carbon is 12u, so its gram atomic mass is 12 grams. The gram atomic mass of a substance represents the mass of 1  mole  of atom (6.023 x 10²³ atoms) of that substance.

The molar mass of a substance is the mass of 1 mole of that substance. The unit of molar mass is grams per mole. The molar mass of an element has 6.023 x 10²³ atoms of the element in it. The molar mass of an element is equal to the gram atomic mass of the element expressed in g/mol.

The amount of a substance whose mass in grams is numerically equal to its molecular mass is called gram molecular mass of that substance. The molecular mass of water (H₂O) is 18u, so its gram molecular mass is 18 grams. The gram molecular mass of a substance represents the mass of 1 mole of molecules (6.023 x 10²³ molecules) of that substance.

The mole concept

Mole is a link between the mass of atoms (or molecules) and the number of atoms (or molecules). A group of 6.023 x 10²³ particles (atoms or molecules) of a substance is called a mole of that substance.

For examples,

• 1 mole of nitrogen atoms (N) = 6.023 x 10²³ nitrogen atoms.
• 1mole of nitrogen molecules (N₂) = 6.023 x 10²³ nitrogen molecules
• The number, 6.023 x 10²³, which represents a mole, is known as Avogadro's Number.
• Number of moles of atoms = Mass of element in grams/ Gram atomic mass of element (or molar mass of element)
• Number of moles of molecules = Mass of substance in grams/ Gram molecular mass of substance (or molar mass of substance)