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Atomic StructureHave you ever wondered what water is made of? You may have seen many a times the symbol H2O and may have often wondered about its meaning. The symbol H2O represents a water molecule. Molecules are extremely small particles.
Isn't it interesting to know that small amounts of water, that you could hold on your palm, may contain more than 100,000,000,000,000,000,000,000 molecules (that is 100 times greater than billion times trillion!)? Water molecules are so small that we fail to see them even with very powerful microscopes.
Now let me tell you something more interesting. Molecules are made up of even smaller particles! These are called atoms. Each water molecule is made of three atoms, two hydrogen atoms and one oxygen atom. In fact every object in your surroundings is made of atoms. Atoms can be thought of as building blocks for all chemical matter.
There are more than 100 types of atoms; they are listed in a periodic table. But how do these atoms differ from one another? How is a hydrogen atom different from an oxygen atom? To answer these questions we have to learn about the particles that constitute an atom.
Atoms are primarily made of three particles; they are neutrons, protons and electrons. Neutrons and protons are present in the central part of the atom. This central part is called nucleus. Electrons are found outside and around the nucleus.
Protons, which are in the nucleus, are assigned a positive charge. The electrons have a charge opposite to that of a proton and hence assigned a negative charge. Neutrons are neutrally charged; i.e. they have no charge.
Atoms always have equal numbers of electrons and protons. Atomic number of an atom is the number of protons present in it. A periodic table arranges the types of atoms based on their atomic numbers (and chemical properties.. you will learn about this later).
Let us look at an oxygen atom now. It is denoted by the 'O' (the O in H2O is oxygen).
It contains 8 protons and 8 electrons. So the atomic number is 8. In addition to protons and electrons oxygen also has 8 neutrons.
Oxygen: Atomic number 8
Now what about the hydrogen atom? It is denoted by the symbol H (the H in H2O is hydrogen). Hydrogen has one electron and one proton, its atomic number is 1. It is the first element in the periodic table.
Hydrogen : Atomic number 1
Atomic Numbers & Atomic Weights