9th Class

      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 more...

         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 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 more...

        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.   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 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 more...

        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:

• All the matters are made up of smallest particles called atoms.
• Atom are indivisible and can neither be created, nor be destroyed.
• Atoms of same elements are identical in shape, size and mass.
• Atoms of different elements have different mass and chemical properties.
• Atoms always combine together in fixed proportion by mass to form the compound.
• In a given compound the relative more...

        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.             Lams of Chemical Combination The chemical reactions of two or more atoms to form new more...

      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.            Physical States of Matter For long time it is believed that the more...