Structure of Atom
Daltons atomic theory proposed that an atom is indivisible and can neither be created nor be destroyed. But after the discovery of subatomic particles such as electron, proton and neutron/ this theory failed. After that it became necessary to discover the structure of atoms. Many scientist proposed various models for atom. The different models of atoms are:: 
Introduction
In this chapter we will discuss about the structure of atoms and will explain the important properties of the atom and molecules. It was only in the 19th century we came to know that atom consists of sub atomic particles, called the charge of the atom. It consists of three subatomic particles, electron, proton, and neutron. The electrons are the negative charge particles, which was discovered by JJ. Thomsons in 1897.
Discovery of Electron
It was discovered by J.J. Thomson in 1897. In his experiment he took a discharge tube at very low pressure and passed electric current of high voltage through it.
Through the gap, a small beam of cathode rays got out of the area of the cathode and anode influence. Next, the beam passed through a long vacuum tube and fell on a fluoroscopic screen leaving there a fluorescent sign. In the vacuum tube, Thomson also put two metal plates connected to a battery. That way he could create voltage between the plates, where the beam had its path. The field was directed perpendicularly to the cathode rays beam. It emerged that under the influence of voltage the beam was deflected (the spot on the screen appeared in a different place. It was the final evidence that cathode rays consisted of charged particles otherwise the beam couldn't be deflected by the electric field. The direction of the deflection also shows the charge of the particles. It emerged to of the negative charge.
It was R.A. Millikan who first measure the charge on electron in 1909, by his famous oil drop experiment. The magnitude of charge on the electron is \[\mathbf{1}{{\mathbf{0}}^{\mathbf{-19}}}\,\mathbf{coulomb}\]. The relative charge of the electron is-1. The mass of the electron is found to be
\[\mathbf{9}\mathbf{.1\times 1}{{\mathbf{0}}^{\mathbf{-31}}}\,\mathbf{kg}\]. The relative mass of an electron is approximately equal to \[\frac{1}{1840}\] of the mass of the hydrogen atom.
Discovery of Proton
The proton was discovered by E. Goldstein in 1886. In his experiment he took a discharge tube and applied high voltage into it.
When he applied high voltage under low pressure, he observed a faint red glow on the wall behind the cathode. These rays were also called the canal rays. When these rays were allowed to pass through the charge plates placed above and below the discharge tube found that these rays were deflected towards the negative plate. He conclude that these rays must possess positive charge and hence were called protons. The charge on proton was found to be \[\mathbf{1}\mathbf{.6\times 1}{{\mathbf{0}}^{\mathbf{-19}}}\,\mathbf{coulomb}\] coulomb and the relative charge was + 1. The mass of proton was found to be \[\mathbf{1}\mathbf{.673\times 1}{{\mathbf{0}}^{\mathbf{-24}}}\,\mathbf{g}\]. The relative mass of proton was found to be 1 amu.
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Separating the Components of Mixtures
The different methods by which we can separate the components of mixtures are : Evaporation, Centrifugation, Decentation, Distillation, Fractional Distillation, Using separation funnel, Chromatography, and Sublimation. The method used is determined by the nature of mixtures. We will discuss each methods separately as below:
Evaporation
This methods is used to separate the dissolved material from the solvent. When we evaporate the solution, the solvent get evaporated and the solute is left behind. For example, we can separate the mixture of salt and water by this methods.
Centrifugation
In this method, when the mixture is spun rapidly, the denser particles are forced to settle at the bottom and lighter particles stays at the top. Therefore, can be separated from each other. For example, we can separate cream from milk by this method.
Decentation
In this method we can separate the insoluble solid from a liquid by allowing the solid to settle down and pouring out the liquid off it. For example, we can separate the mixture of sand and water or gravel and water etc.
Distillation
This method is used to separate a mixture of two liquid of different boiling points. In this method, we first heat the mixture of liquids and collect the vapour of the liquid/ which has low boiling points and evaporate first and then condensed it to get back the liquid.
Fractional Distillation
This method is used for separating the mixture of two or more liquids having different boiling points. It is done by using fractionating column. In this process distillates are collected in fractions, boiling at different temperatures.
Using Separating Funnel
This method is used to separate the mixture of two liquids, which are not miscible. In this method the mixture is put into the funnel and is allowed to settle. When it settles down the lighter liquid forms the upper layers and the heavier liquid forms the lower layers. The tap of the funnel is open and the lower layer is carefully drained out and thus, the liquids is separated.
Chromatography
This method is used to separate the mixture of solute formed by distribution of dissolved materials between two immiscible phases, in which one is movable and other is stationary. For example, we can separate the components of dyes by this method.
Sublimation
In this method the solid directly gets converted into gas without getting more... 
Compounds
It is a pure substance, in which two or more elements combine chemically together in a fixed proportion by mass to form the compound. The properties of compound are different from the properties of the elements.
For example, the elements like hydrogen and oxygen are found in gaseous state, but when they combine to form water, it turns to liquid state. Similarly if we heat iron filing and sulphur powder, a black compound of iron sulphide is formed. Now, if we bring a bar magnet near the compound we find that it is not attracted by the iron in the compound so formed. The other example, if we add carbon disulphide to the sulphur, we find it is not dissolved in it, which shows that sulphur is not showing its property. Thus, we can say that the properties of compound is entirely different of the it’s elements forming it.
Properties of Compound
Following are the properties of compound:
Solutions
It is a homogenous mixture of two or more substance in which one substance is liquid. It consists of two parts, solvent and solute. The solvents are that part of solution in which something has been dissolved and the substance which has been dissolved into it, is called the solute. For example, in the solution of salt and water, salt is solute as it is dissolved in water and water is solvent.
The solution is basically of two types, such as saturated and unsaturated. Saturated solutions are those in which no more solute can be dissolved. On the other hand, the solution in which more solutes can be dissolved are called the unsaturated solution. The amount of solute present in the saturated solution at the given temperature is called its solubility.
The concentration of solution is defined as the amount of solute presents in the given volume of solvent.
Concentration of solution \[=\,\frac{Mass\,of\,solute}{Mass\,of\,solution}\]
Percentage by mass \[=\,\frac{Mass\,of\,solute}{Mass\,of\,solution}\times 100\]
Percentage by volume \[=\,\frac{Volume\,of\,solute}{Volume\,of\,solution}\times 100\]
Properties of Solution
Introduction
In our daily life we come across several types of matters in our surroundings. It is very difficult to say which of the matters is pure. Even the eatables, which we purchase from the market is not found to be pure and is adulterated with undesirable materials that are harmful for us. The pure substance is the substance which are made up of only one type of atoms or particles. All the matters are divided into two categories as mixture and pure substance.
Mixture
When two or more different types of substance are mixed together, not in any fixed proportion, it is called mixture. Mixture is of two types Homogenous and heterogenous mixtures. In mixtures the components cannot be separated by physical means.
Homogenous Mixture
The mixture having uniform composition is called the homogenous mixture. If we dissolve sugar or salt in water, it gets dissolved completely in water and particles of sugar are not visible to us our naked eyes. Hence it is a homogenous mixture. It has no visible boundaries of separation between various constituents and usually exist in one phase.
(1) Air is a mixture of gas in gas.
(2) Aerated water \[(C{{O}_{2}}+{{H}_{2}}O)\] is a mixture of gas in liquid.
(3) Kerosene, petrol, alcohol, water, etc are mixture of liquid in liquid.
(4) Alloys such as bronze, steel, brass etc are mixture of solid in solid.
(5) Sugar solution, salt solution are mixture of solid in liquid.
(6) Amalgamated Zinc is a mixture of liquid in solid.
(7) Adsorption of hydrogen gas in palladium is a mixture of gas in solid.
Heterogenous Mixture
The mixture having non uniform composition are called heterogenous mixture. In this case, each constituent particles are visible in our naked eyes. We can separate them by physical means. For example if we mix rice, sand and pulse the mixture will be heterogenous and each constituent is visible in our naked eyes and we can separate them either by hand picking or any other means.
Properties of Mixture
Following are the properties of mixtures:
Which one of the following is a homogenous mixture?
(a) Salt solution
(b) Muddy water
(c) Chalk in water
(d) more... 
Atomic Mass
It is the mass of an atom of an element or it is defined as the quantity of mass equal to the one twelfth of the mass of an atom of carbon 12.
Relative Atomic Mass
It is defined as the number of times an element of an atom is heavier than one twelfth of an atom of carbon 12.
Relative atomic mass \[=\frac{\text{Mass of one atom of the element}}{\frac{1}{12}\times \text{Mass of one atom of C}-\text{12}}\]
Gram Atomic Mass
The atomic mass of an element expressed in gram is called the gram atomic mass of that element.
Molecules
Molecules are the smallest particle of the substance, element or compound which can exist in Free State under the normal condition of temperature and pressure. The total number of atoms, of all types, present in one molecule of a substance is called its atomicity.
For example:
Atomicity of \[{{O}_{2}}\] is 2 and that of \[C{{O}_{2}}\] is 3. There are different types of molecules. The molecules having only one kind of atom is called monoatomic molecules, such as \[He,\,Ne,\,\,Ar\] etc.
The molecules containing two atoms are called diatomic molecules, such as \[{{O}_{2}},\,\,{{H}_{2}},\,\,C{{l}_{2}}\] etc.
The molecules containing three atoms are called triatomic molecules, such as \[C{{O}_{2}},\,\,{{O}_{3}},\,\,{{H}_{2}}O,\,\,N{{O}_{2}}\] etc.
The molecules containing four atoms are called tetratomic molecules, such as \[{{H}_{2}}{{O}_{2}},\,\,N{{H}_{3}},\,{{P}_{4}}\] etc.
The molecules containing five atoms are called pentatomic molecules, such as \[NH{{O}_{3}},\,C{{H}_{4}}\] etc.
The molecules of an atom contains same kind of atoms. For example \[{{O}_{2}},\,\,{{H}_{2}},\,C{{l}_{2}}\] are all molecules of the atoms.
The molecules of the compound contains atoms of different elements. For example \[C{{O}_{2}},\,\,{{H}_{2}}O,\] etc.
Molecular Mass
The molecular mass of a substance is defined as the sum of atomic mass of all the atoms present in the substance.
For example:
The molecular mass of \[C{{O}_{2}}=1\times 12+2\times 16=44\,\,\text{amu}\].
Gram Molecular Mass
The molecular mass of the substance expressed in gram is called the gram molecular mass.
Mole Concept
A mole is a unit for expressing the smallest unit of matter, such as proton, electron, atoms, ions, etc. The number of atoms present in one gram atom of an element is equal to the \[6.023\times {{10}^{23}}\]. Thus one mole of a substance is equal to \[6.023\times {{10}^{23}}\] atoms. This constant is also called the Avogadro's constant or
Avogadro’s number. Hence we can define mole as the amount of substance which contains same number of particles as the number of carbons atoms present in 12g of C-12 isotopes of carbon.
Thus, 1 mole = gram atomic mass of atom \[=6.023\times {{10}^{23}}\] atoms more... 
Atoms
According to modern atomic theory, an atom is the smallest particle of elements. It takes parts in the chemical reaction and maintains its identity throughout all physical and chemical changes. Since the atoms of elements are quite reactive, they do not exist in Free State except for noble gases. All the atoms consist of subatomic particles called electron, proton and neutron. The number of electrons and protons in an atom is always found to be the same. The electron revolve around the nucleus in a fixed orbit and the proton and the neutron are present in the nucleus of an atom. The atoms are very smaller is size and cannot be seen by the naked eyes. The size of an atom is measured by its radius called the atomic radius. The atomic radius of smallest atom Hydrogen is 0.37 x 10-10 m or 0.037 nm. 1 nm = 10-9 m.
The atoms are normally denoted by symbols. It was Daltons who introduced the use of symbol to denotes the atoms of different elements. Dalton's symbol for some of the elements are given below:
| Element | Symbol |
| Hydrogen |  |
| Carbon |  |
| Oxygen |  |
| Nitrogen |  |
| Sulphur |
Dalton's Atomic Theory
John Dalton provided the basic theory about the nature of matter. He used the idea of divisibility of matter and called the smallest particle of matter as atoms. It was based on the theory of chemical combination. He also provided the explanation on laws of conservation of mass and laws of constant proportion. According to Daltons atomic theory all the matters is composed of smallest particles called atom.
The postulates of this theory are:
Merits of Dalton Atomic Theory
To form water. Hydrogen and oxygen combine in the ratio 1:8. Find the mass of oxygen required to react completely with 3 g of hydrogen.
(a) 4 g
(b) 8 g
(c) 16 g
(d) 24 g
(e) None of these
Answer: (D)
Introduction
All the matters found in this universe are made up of small particles called atoms. The idea of divisibility of matters came into light around 500 BC. An Indian Philosopher, Maharishi Kanad, in his postulate said that if we go on dividing the padarth till it is not any more divisible, then we come across the particles which is not further divisible is called parmanu. This smallest parmanu in Greek word is called atom, which means indivisible. All this explanation was based on philosophical consideration and not on experimental work, till the end of eighteenth century, when perhaps the first scientific defination of atoms came into existence and difference between element and compound was established.
Laws of Conservation of Mass
This law was given by A. Lavoisier. He states that during a chemical reaction mass can neither be created nor be destroyed. For example:
\[CaC{{O}_{3}}\,\text{(rectant}\,100g)\to CaO\,(56g)+C{{O}_{2}}\,(44g)\,\text{(product)}\]
Thus we see that total mass of reactant is equal to the total mass of product. A practical example of this is: take a piece of ice cube and measure its weight. Put it in a flask and leave it to melt. When it melts completely again measure its weight. You will find the weight in both the case is approximately same. Thus we can say that the law of conservation of mass is also valid in case of physical change.
For example:
Take some amount of iron filing and sulphur powder of desired weight. Put them in a china dish and heat it. The compound so formed is iron sulphide and measure its weight. We find that the weight in both the case is approximately same. Thus we can say that law of conservation of mass is also valid for chemical change.
Introduction
Everything in this universe is made up of matter. All the things we see in our surroundings occupies space, and has certain mass and volume. Early Indian philosopher used to says that, matters are classified in the form of five basic elements, called panch tatva. These panch tatva includes air, water, earth, sky and fire. According to them everything whether living or non living is made up of only these five things. But modern classification is based on the physical and chemical properties of the matter. Chemistry deals with the study of matters. It involves many aspects of matters which are based on its classification and on the chemical composition into three main categories namely elements, compounds and metalloids.
Characteristics of Particles of Matter
The different characteristics of particles of matter are:
