Chemistry

Matter in Our Surroundings

Elements

An element is a substance which cannot be split up into two or more simpler substances by the usual chemical methods of applying heat,light or electric energy. For example, hydrogen is on element because it cannot be split up into two or more simpler substances by the usual methods of carrying out chemical reactions by applying heat, light or electricity. Similarly, oxygen is an element because it cannot be broken down into simpler substances bv chemical methods. ()n the other hand, water is not .111 element because it can be split up into two simpler substances, hydrogen and oxygen, by electricity
An element cannot be split up into two (or more) simpler substances because it is made of only one kind of atoms. This gives us another definition of an element which can be stated as follows : An element is a substance which is made of only one kind of atoms. For example, copper metal is made of only one kind of atoms called 'copper atoms', so copper metal is an element (see figure 5). Similarly, iron metal is made of only iron atoms, so iron metal is also an element (see Figure It is clear from the above discussion that an element is made of same kind of atoms. In other words, all the atoms of an element are identical.The atoms of different elements differ in size and composition.
There are 115 elements known at present, out of which 92 elements occur in nature, while the remaining 23 elements have been prepared artificially. Every substance in this world is made up of one or more of these elements. Some of the common elements are : ludrogen, helium, oxygen, nitrogen, carbon, sulphur.phosphorus, chlorine, bromine, iodine, sodium, potassium, magnesium, calcium, aluminium, copper, silver,gold, zinc, iron, silicon, tin and mercury'. Diamond and graphite are also elements. They are the allotropic forms of carbon element. Each element is represented by a separate symbol.
Elements can be solids, liquids or gases. Some elements are solids, some elements are liquids whereas other elements are gases at the room temperature. For example, sodium and carbon elements are solids,mercury and bromine elements are liquids, whereas hydrogen and oxygen elements are gases, at the room temperature. In fact, majority of the elements are solids. Eleven elements are gases whereas only two elements (mercury and bromine) are liquids at the room temperature.
Most of the materials around us are made up by the combination of two or more elements. For example, water is a common material which is made up of two elements: Hydrogen and Oxygen. Similarly, sugar is a common material which is made up of three elements: Carbon, Hydrogen and Oxygen.Just as 26 letters of the 'English alphabet7 combine in various different ways to make a very large number of words, in the same way, a few elements combine together in various different ways to make an extremely large number of materials and objects. Even the human body is made up of complex compounds formed by the combination of only certain elements. For example, the human body contains 65% oxygen element,18% carbon element, 10% hydrogen element, 3% nitrogen element, 2% calcium element and 2% other elements.

Notes

Matter in Our Surroundings - Notes

1. 9. Non-Metals Have Low Densities.