Chemistry Short Questions And Answer For Exam Preparation
Chemistry short Questions and Answer for Exam Preparation
Atomic Number and Mass Number
Atomic number:The number of protons or electrons in the nucleus is called the atomic number.It is represented by ‘Z’.
Mass Number:The total number of protons and neutrons is called the mass number or the nucleon number.It is represented by ‘A’ and it determines the mass of the nucleus.
Relative Atomic Mass and Atomic Mass Unit
Atomic Mass Unit :The atomic mass unit is the mass equa to 1/12th of the
mass of a C atom.
Relative Atomic Mass Unit :The relative atomic mass (Ar) of an element is defined as the average relative mass of an atom of the element compared with an atom of 12C taken as 12 atomic mass units.
The average mass of an element in atomic mass units is known as its atomic mass.
Empirical and Molecular Formula
Chemical Formula :A chemical formula is a shorthand notation of a compound.
Types of Chemical Formula
There are three types of chemical formulae:
A shorthand notation for the molecule of a substance in terms of the symbols.It also represents the actual number of atoms of each element present in one molecule of thaat substance.
The simplest formula of a substance which gives the relative number of atoms of each element present in the molecule of that substance is called as empirical formula.
Formula Mass of Substance
Formua mass of a substance is equal to the sum of the atomic masses of all the atoms present in the empirical formula.
Relative Molecular Mass and Formula Mass
Relative Molecuar Mass(Mr) :The relative molecular mass(Mr) of a substance is the average relative mass of its molecule as compound with the mass of a 12C atom taken as 12 units.
Molecular Mass(M) :
The average mass of a molecule of a substance in atomic mass unit is called its moecular mass(M).
Formula Mass :The average mass of a formula unit of a substance in atomic mass units is called its formula mass.
Molar Mass :
The average mass of one mole of any material is called its molar mass.
The common chemical species are ions,molecular ions,free radicals and neutral molecules.
A species having positive or negative charge is called an ion.
Types of ions
There are two types of ions:
1.Postive ion or Cation
2.Negative ion or Anion
1.Positive ion or Cation
When atom lose one or more electrons,positive ions are formed.Cations may have +1,+2,+3,+4 charges.
2.Negative ions or Anion
When one or more electrons are added to an isolated neutral atom,negative ions are formed.Anions may have -1,-2.-3 charges.
Any molecular species having positive or negative charge is called molecular ion.
Formula Unit :A formua unit,as the name implies,is one unit,where atom,ion or molecule corresponds to given formula.
A free radical is a molecule,an atom or an ion containing odd number of electrons.