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Valency, , The combining capacity of the atoms or their, tendency to react and form molecules with, atoms of the same or different elements is, known as valency of the atom., , The electrons present in the outermost shell of, an atom are known as valence electrons., , For example, the number of electrons in the, outermost shell of hydrogen is 1, and in, magnesium is 2. So the valency of hydrogen is, 1 & magnesium is 2., , Atomic Number, , The number of protons found in the nucleus of, an atom is termed as the atomic number. It is, denoted by the letter ‘Z’., , Mass Number, , Protons and neutrons are present in the, nucleus, so the mass number is the sum of the, total of protons and neutrons., , Isotopes, , Isotopes are defined as the atoms of the same, element, having the same atomic number but, different mass numbers., , For example: Hydrogen have three Isotopes, , Isobars, , Atoms of different elements with different, atomic numbers, which have the same mass, number, are known as isobars., , For example, Calcium and Argon: both have the, same mass number — 40, , 20Ca*° and 18Ar*°, , 2022-01-14, From vivo Notes