atomic number

Representative elements are those elements whose inner shells are complete and whose outer shell (valency shell) has 1 to 7 electron..

The rules used for the calculation of oxidation number of an atom in a molecule are: The oxidation number of an element in the free or elementary state is always zero. For example, oxidation numbers of helium in He, hydrogen in H 2 , oxygen in O 2 , iron i..

The total number of protons and neutrons present in one atom of an element is known as its mass number. Mass number = number of protons + number of neutrons It can also be said that: Mass number = Atomic number..

The number N A , given by N A = 6.023x10 2 3 mol - 1 is called Avogadro's number, named after Italian scientist Amadeo Avogadro (1776-1856), who suggested that all gases contain the same number of atoms or molecules when they occupy the same volume under..

Atomicity is the number of atoms of an element present in one molecule of that element. They can be monoatomic (He), diatomic (H 2 ), triatomic (O 3 ) and polyatomic (S 8 ..

The radius of a Hydrogen atom is equal to 1 × 10 -1 angstrom. Write this number in standard form. => 0.01 or 0.001 or 0.0001 or 0.1..

The diameter of an atom is 0.0000000125 cm. Which one of the following shows this number in scientific notation? => 1.25 × 10 - 8 cm or 1.25 × 10 - 10 cm or 12.5 × 10 - 8 cm or 125 × 10 - 8 cm..

The distance from the centre of the nucleus to the outermost shell of an atom is called the atomic radius of that atom. Electrons in the same period progressively increase from left to right, as the atomic number increases, e.g., in the 3 rd p..

The distance from the centre of the nucleus to the outermost shell of an atom is called the atomic radius of that atom (Fig. 2.1..

Isotopes - It is interesting to note that atoms of a given atomic number can have different number of neutrons. Some examples are listed belo..