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When talking about atoms, Dalton's name comes first. According to Dalton all matter is made of tiny indivisible particles, which are called atoms. That is, an atom is that part of matter that cannot be broken. As we divide a matter, it reaches a point where it can no longer be divided. This is the atom. All matter is made up of these atoms. But with the development of technology, the concept of atom has changed.

Many bricks are used to build a wall. Comparing these bricks with atoms helps us to understand what an atom is. Although the atom is not as big as a brick. In fact, atoms are so small that they cannot be seen with the naked eye. However, if we think of walls as matter, then the atom is a brick. It is said only for ease of understanding.

Along with the development of science and technology, we are introduced to the smallest particles of an atom. Now we know that atom consists of neutrons protons electrons. These particles have mass and charge. Proton and neutron have almost equal mass. The mass of an electron is thousands of times less than the mass of a proton. But electrons and protons carry equal and opposite charges even though their masses are so small and so large.

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Along with the development of science and technology, we are introduced to the smallest particles of an atom. Now we know that atom consists of neutrons protons electrons. These particles have mass and charge. Proton and neutron have almost equal mass. The mass of an electron is thousands of times less than the mass of a proton. But electrons and protons carry equal and opposite charges even though their masses are so small and so large. A proton acquires a positive charge and an electron acquires a negative charge. A neutron is charge neutral

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Protons and neutrons are held together in the center of the atom. The center of an atom is called the nucleus. Electrons reside outside the atom's nucleus and move around. This occurs for protons and electrons of opposite charge. Electrons revolve around the nucleus because protons have a positive charge and electrons have a negative charge.

We know that positive charge and negative charge attract each other. Protons and electrons also attract each other in the same way. This force of attraction holds the elements of an atom together. Since an atom has equal number of protons and electrons, it has no net charge. A proton has the same charge as an electron, so its total charge will be zero. But atoms that have extra electrons or no electrons have a net charge. If an atom has two electrons opposite to one proton, the two electrons will have twice the charge of the proton. If there are no electrons then only protons will have charge. That is why this type of atom has a net charge. These are called ions. Ions carry negative charge or positive charge. As a result they attract each other

To know more about the mass of atoms, it is necessary to know how atoms are measured. The unit of atomic mass is amus. The mass of an atom is very small, so its units are also small. One amus is one twelfth of the mass of one carbon 12. This is a small number expressed as 1.66 x 10'-27 kg.

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Isotopes of an element have different numbers of neutrons in their nucleus

All isotopes of one element have identical chemical properties. This means it is difficult to separate isotopes from each other by chemical processes. However, the physical properties of the isotopes, such as their masses, boiling points, and freezing points, are different. Isotopes can be most easily separated from each other using physical processes. source

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A hydrogen atom that has a nucleus has a mass of 1.008 amu. A hydrogen atom that has two neutrons in its nucleus for a single proton has a mass of 2.014 amu. It is called deuterium. Again, the nucleus of a hydrogen atom has three neutrons for a single proton. Their mass is 3.016 amu. They are called tritium. All these isotopes of hydrogen have one electron each.

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The sum of the number of protons and neutrons in the nucleus is the mass number of that element. Different isotopes of an element have different mass numbers because they have different numbers of neutrons in their atomic nuclei. Hydrogen is labeled as H1, deuterium as H2 which is clearly visible in the above diagram.

Atomic numbers are used to distinguish elements. The modern periodic table of elements shows the various elements arranged in increasing order of atomic number as shown in the figure below.

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Scientists always use this periodic table. By referring to the atomic number, they know how many protons and neutrons are in the nucleus of that element. So this table is useful in several ways. Like helium 2 means a helium atom contains 2 protons. Gold has an atomic number of 79, which means it has 79 protons in its nucleus. There are currently 118 elements in the periodic table. Everyone from students to scientists use the periodic table

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Source NASA 's website

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