![]() These can thus flow and expand more than solids when heated The molecules have moderate intermolecular force of attraction which is lesser than solids. The molecules have very strong intermolecular force of attraction due to which they are rigid, and expand very less on heating The molecules are very loosely packed and hence gases have no definite shape, no definite volume, very low density and very high compressibility Density of liquids is slightly lesser than solids and therefore they are slightly more compressible than solids The molecules are loosely packed hence liquids do not have definite shape and take the shape of the container. The molecules are closely packed and therefore solids have a definite shape, definite volume, high density and negligible compressibility Though atom is composed of sub-atomic particles, yet it is the smallest particle, which takes part in chemical reactions. Such atoms of different elements, which possess same mass, are called isobars.Ītom is the smallest unit, which takes part in chemical reactions. For example, relative mass of calcium and argon is same (40 a.m.u.). There are certain atoms of different elements, which possess same relative masses. Such atoms of the same element, which possess different masses, are called isotopes.Ītoms of different may be similar in one or more respects. For example, we have two different types of atoms of chlorine, with relative masses 35 a.m.u. Atoms of same element may possess different relative masses. It has been found that an atom has a complex structure and is composed of sub-atomic particles such as electrons, protons and neutrons.Ītoms of the same element may not be similar in all respects. The main modifications made in this theory are as follows :Ītom is no longer considered to be indivisible. It did not make any distinction between ultimate particle of an element that takes part in reactions (atom) and ultimate particle that has independent existence (molecule). It failed to explain Gay Lussac’s law of combining volumes. It failed to explain the nature of forces that bind together different atoms in a molecule. It could not explain how and why atoms of different elements combine with each other to form compound-atoms or molecules. It failed to explain how atoms of different elements differ from each other, i.e., it did not tell anything about structure of the atom. The main failures of Dalton’s atomic theory are : Matter is made up of extremely small, indivisible particles called atoms.Ītoms of same substance are identical in all respects, i.e., they possess same size, shape, mass, chemical properties, etc.Ītoms of different substances are different in all respects, i.e., they possess different sizes, shapes, masses, chemical properties, etc.Ītom is the smallest particle that takes part in chemical reactions.Ītoms of different elements may combine with each other in a fixed, simple, whole number ratio to form compound atoms.Ītoms can neither be created nor destroyed, i.e., atoms are indestructible. The main points of Dalton’s atomic theory are as follows:
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