Hydrogen is the most abundant element in the universe. It is present in combined state as water, coal, animal and vegetable matter. Chemistry is intended to make students accustomed to the properties, reactions, uses of hydrogen and other relative factors of hydrogen. Hydrogen is the first element in the periodic table and the lightest element with just one proton and one electron. Besides, hydrogen is an essential element as it is the most common item that makes up more than 80 per cent of the mass of the entire universe. All organic compounds contain hydrogen as an essential constituent. Hydrogen has three isotopes. Therefore if you are a student of chemistry, it is vital to know all about this element.