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 12 mass of a C atom. 6 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. Atomic Mass 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: 1.Molecular Formua 2.Empirical Formula 3.Structural Formula Molecular Formula 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. Empirical Formula 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. Chemical Species The common chemical species are ions,molecular ions,free radicals and neutral molecules. Ion 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. Molecular Ion 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. Free Radical A free radical is a molecule,an atom or an ion containing odd number of electrons. Reply With Quote
Posted on: Sat, 22 Mar 2014 15:40:05 +0000
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