- CHEMICAL FORMULAE
- MOLECULAR MASS
- AVOGADRO CONSTANT OR AVOGADRO NUMBER
- LAW OF CONSERVATION OF MASS
- LAW OF DEFINITE PROPORTIONS
- STRUCTURE OF THE ATOM
- THOMSON’S MODEL OF ATOM
- RUTHERFORD’S MODEL OF ATOM
- BOHR’S MODEL OF ATOM
- ATOMIC NUMBER
- Mass Number
- CHEMICAL REACTIONS & EQUATIONS
- CHEMICAL EQUATION
- TYPES OF CHEMICAL REACTION
- COMBINATION REACTION
- DISPLACEMENT REACTION
- OXIDATION AND REDUCTION
Distillation – 02
- A charged particle is known as ion.Ionic bond, also called electrovalent bond, type of linkage formed from the electrostatic attraction between oppositely charged ions in a chemical compound. Such a bond forms when the valence (outermost) electrons of one atom are transferred permanently to another atom. The atom that loses the electrons becomes a positively charged Ion (Cation), while the one that gains them becomes a Negatively Charged Ion (Anion). A brief treatment of ionic bonds follows.
- A chemical formula of a compound demonstrations its constituent elements and the number of atoms of each combining element.
- The chemical formula of a compound is the symbolic representation of its Composition.
- The combining capacity of an element is known as its ‘VALENCY.’
- The molecular mass of a substance is calculated by taking the sum of the atomic masses of all the atoms in a molecule of respective substance.
For example, the molecular mass of water is calculated as −
- Atomic mass of hydrogen = 1u
- Atomic mass of oxygen = 16 u
- The water contains two atoms of hydrogen and one atom of oxygen.
- Molecular Mass of Water is = 2 × 1+ 1×16 = 18 u (u is the symbol of molecular mass).
Formula Unit Mass
- The formula unit mass of a substance is calculated by taking the sum of the atomic masses of all atoms in a formula unit of a compound.
AVOGADRO CONSTANT OR AVOGADRO NUMBER
- Avogadro was an Italian scientist who had given the concept of Avogadro Number (also known as Avogadro Constant).
- The number of particles (atoms, molecules, or ions) present in 1 mole of any substance is fixed, and its value always calculated as 6.022 × 1023.
- In 1896, Wilhelm Ostwald had introduced the concept of ‘mole;’ however, mole unit was accepted to provide a simple way of reporting a large number in 1967.
LAW OF CONSERVATION OF MASS
- During a chemical reaction, sum of the masses of the reactants and products remains unchanged, which is known as the ‘Law of Conservation of Mass.’
LAW OF DEFINITE PROPORTIONS
- In a pure chemical compound, its elements are always present in a definite proportion by mass, which is known as the ‘Law of Definite Proportions.’
STRUCTURE OF THE ATOM
- By 1900, it was discovered that the atom was not a simple, indivisible particle, but rather it contains sub-atomic particles.
- J.J. Thomson discovered the sub-atomic particle namely ‘Electron.’
- J.J. Thomson was the first person who proposed a model for the structure of an atom.
- In 1886, E. Goldstein discovered the presence of new radiations in a gas discharge and named them canal rays.
- Another positively charged sub-atomic particle was discovered with experiments of canal rays and named it proton.
THOMSON’S MODEL OF ATOM
- Thomson proposed that an atom consists of a positively charged sphere and the electrons (negative charge) are embedded in it (as shown in the image given below).
- Further, Thomson said that the negative and positive charges are equal in magnitude. Thus, the atom as a whole is electrically neutral.
RUTHERFORD’S MODEL OF ATOM
- E. Rutherford is popular as the ‘Father’ of nuclear physics.
- Rutherford is largely known for his work on radioactivity and the discovery of the nucleus of an atom with the gold foil experiment (as shown in the image given below.
- Rutherford said that in an atom, there is a positively charged center known as the nucleus. Rutherford said that nearly all the mass of an atom exists in in the nucleus. According to Rutherford, the electrons revolve around the nucleus in well-defined orbits.
BOHR’S MODEL OF ATOM
- Neils Bohr further extended Rutherford’s model and improved his drawbacks.
- According to Bohr, only certain special orbits known as discrete orbits of electrons, are allowed inside the atom. Bohr said that electrons do not radiate energy while revolving in discrete orbits. Bohr named orbits or shells as energy levels (as shown in the image given below).
- Bohr represented these orbits or shells are by the letters K, L, M, N,… or the numbers, n = 1,2,3,4,….
In 1932, J. Chadwick discovered a new sub-atomic particle i.e. neutron.Neutron has no charge and a mass nearly equal to that of a proton. Neutrons are present in the nucleus of all atoms, except hydrogen.
Electrons Distributed in Different Orbits (Shells)
- The maximum number of electrons that can be present in a shell is given by the formula 2n2.
- ‘n’ is the orbit number or energy level index, i.e. 1, 2, 3,….
- According to the given formula −
- First orbit i.e. K-shell will be = 2 × 12 = 2
- Second orbit i.e. L-shell will be = 2 × 22 = 8
- Third orbit i.e. M-shell will be = 2 × 32 = 18
- Fourth orbit i.e. N-shell will be = 2 × 42 = 32
- Likewise, the maximum number of electrons that can be accommodated in the outermost orbit is 8.
- Electrons are not filled in a given shell, unless the inner shells are filled. It means, the shells are filled in a step-wise manner; starting from inner shell to outer shell.
- The electrons, those are present in the outermost shell of an atom, are known as the valence electrons.
- According to Bohr-Bury model, the outermost shell of an atom can have a maximum of 8 electrons.
- The total number of protons, present in the nucleus of an atom, is known as atomic number. The number of protons of an atom determines the atomic number. Atomic number is denoted by ‘Z’. Protons and neutrons collectively are known as nucleons.
- The sum of the total number of protons and neutrons, present in the nucleus of an atom, is known as mass number.
- Atoms of different elements with different atomic numbers, which have the same mass number, are known as Isobars. E.g. calcium’s atomic number is 20and argon’s atomic number is 18; further, the number of electrons in these atoms is different, but the mass number of both these elements is 40.
CHEMICAL REACTIONS & EQUATIONS
- A process in which one or more chemical substances react with other chemical substance and converted to one or more different substances is known as chemical reaction.
- A chemical equation is the symbolic demonstration of a chemical reaction; it is represented through symbols and formulae. E.g.
Magnesium + Oxygen = Magnesium Oxide
Mg + O2 = MgO
- The substances magnesium and oxygen are known as reactants and the result of reaction, i.e., magnesium oxide is known as product.
- Remember, the total mass of the elements present in the products of a chemical reaction has to be equal to the total mass of the elements present in the reactants.
- The number of atoms of each element always remains same, before and after the chemical reaction.
TYPES OF CHEMICAL REACTION
- Following are the major types of chemical reaction −
- Combination Reaction
- Decomposition Reaction
- Displacement Reaction
- Let’s discuss each of them in brief −
- When two or more substances (i.e. elements or compounds) react to form a single product, such reaction is known as combination reaction. E.g.
(Quick lime) (Slaked lime)
- As illustrated in the above reaction, calcium oxide and water reacted (or combined) to form a single product, known as calcium hydroxide.
- The chemical reaction in which heat is also released along with the formation of product is known as exothermic chemical reactions.
- The reaction, in which a single reactant breaks down into simpler products, is known as a decomposition reaction.
- In the above given reaction, Ferrous Sulphate Crystals (i.e. FeSO4, 7H2O), when heated, it loses water and the color of the crystals changes. Finally, it decomposes into ferric oxide (Fe2O3), sulphur dioxide (SO2) and sulphur trioxide (SO3).
- The reaction, in which an element displaces or removes another element, is known as displacement reaction. E.g.
Fe(s) + CuSO4(aq)→FeSO4(aq)+Cu(s)
(Copper sulphate) +(Iron sulphate)
- In the above given reaction, iron displaced copper from copper sulphate solution and forms Iron sulphate.
OXIDATION AND REDUCTION
- If a substance gains oxygen during a reaction, it is known as oxidation. On the other hand, in a reaction, if a substance loses oxygen, it is known as reduction. E.g.
- In the above given reaction, the copper oxide loses oxygen and hence reduced (i.e. reduction); on the other hand, hydrogen gains oxygen and hence oxidized (i.e. oxidation).
When a metal is attacked by substances found in the immediate environment, such as moisture, acids, etc., it is known as corrosion. E.g. the black coating on silver, the green coating on copper, etc.,
- When fats and oils are getting oxidized, the process is known as rancidity. Their smell, taste, color, etc. also change; likewise, it made food unsafe for consumption.