In our environment, we see iron nails, sulphur roll, copper wire, aluminium sheets, etc. we also breathe in oxygen (air) to stay alive. These substances: iron, sulphur, copper and oxygen, are referred to as elements.
Elements are substances that cannot be separated into simpler substances.
Any substance that contains only one kind of an atom is known as an element. Salt is made up of the elements sodium and chloride. Water is made up of the elements hydrogen and oxygen.
Each element is represented by a unique symbol. The notation for each element can be found on the periodic table of elements.
The elements can be divided into three categories that have characteristic properties: metals, nonmetals, and semimetals. Most elements are metals, which are found on the left and toward the bottom of the periodic table. A handful of nonmetals are clustered in the upper right corner of the periodic table. The semimetals can be found along the dividing line between the metals and the nonmetals.
Elements are made up of atoms, the smallest particle that has any of the properties of the element. John Dalton, in 1803, proposed a modern theory of the atom based on the following assumptions.
|1. Matter is made up of atoms that are indivisible and indestructible.|
|2. All atoms of an element are identical.|
|3. Atoms of different elements have different weights and different chemical properties.|
|4. Atoms of different elements combine in simple whole numbers to form compounds.|
|5. Atoms cannot be created or destroyed. When a compound decomposes, the atoms are recovered unchanged.|
These are the first 20 elements and their symbols, listed in order-
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