Hello students in this lesson, let us learn about the discovery and occurrence of hydrogen. We know something about hydrogen by now that we that hydrogen is an element it is inflammable with a pop sound and so many more things, but have you ever wondered this hydrogen gas who must have discovered this gas, it was Robert boyle. So the first person to discover this gas was Robot boyle in the year 1672, Robert boyle did an experiment with metal and an acid and he found that is a colourless gas is given up, but there was nothing known about this gas after that. Then in 1766, there was another scientist called Henry Cavendish, Henry cavendish in the year 1766, studied this metal acid reaction and found out that the gas, that is evolved catches fire, that means it burns, it is combustible and it burns with the pop sound. So Henry cavendish named the gas as inflammable air. Inflammable means a substance that catches fire very soon. So inflammable air, it was termed as, then years later in 1783, in 1783 Antoine lavoisier, found out that hydrogen is a part of water molecule, water is made up of hydrogen and oxygen, so he found out that hydrogen as an important part of water, so he named the inflammable air as hydrogen, where the greek word hydro means ‘water’. So, initially the hydrogen gas was discovered by Robert boyle, he created hydrogen gas by mixing metal and acid, then further on studying this gas, Henry Cavendish named the gases in flammable air because hydrogen gas burns, it is combustible, than years later Antoine lavoisier in a 1783 name the gas as hydrogen gas because it is an integral part of water. Now coming back to Henry Cavendish, hydrogen is either an element compound or mixture, it was actually first recognized by Henry Cavendish, he said that hydrogen has elementary properties, it has properties of elements. So this is how hydrogen was discovered. Now let us move ahead and see the occurrence of hydrogen in our atmosphere as well as in the earth’s crust. Now let’s talk about the occurrence and when we talk about occurrence of hydrogen, hydrogen can either exist in the free state or it can exist in the combined state. In the combined state as it will always be mixed with something or the other when it is naturally occurring and in the free state as it it is naturally occurring in only hydrogen forms, so that’s a free state. So in the atmosphere and in the earth’s crust, hydrogen is founding little traces, it is not in much amount around us. So in the atmosphere, here I’m talking about the earth’s atmosphere, so it is only 0.01 percent of the atmosphere which is made up of hydrogen. Then we talk about earth’s crust, earth’s crust is made up of only 0.98 percent of hydrogen, then volcanic gases, from volcanic gases also we can get hydrogen, volcanic gases contain about 0.025% of hydrogen and the atmosphere in the sun and the stars, around the sun and the stars contain 1.1 percent of the hydrogen. So in the free state this is how hydrogen can exist and in so much of proportion. Now let’s come to the combined state, the first combine state in which hydrogen can occur is in the plant tissues, plant tissues are made up of hydrogen, carbon, oxygen, nitrogen, these elements, these are the main elements with which plant tissues are made, the compounds are made up of carbon, hydrogen, nitrogen and oxygen. Let’s come to the second part, the proteins in humans beat in animals, these proteins are that made up of hydrogen, nitrogen, carbon. So hydrogen is an integral part and beat any hydrocarbon, hydrocarbon are compounds containing hydrogen and carbon in them. All these hydrocarbons have hydrogen and carbon and they are the compounds which are present in almost all the organic compounds. Organic compounds come from plants and animals, living systems, so all these compounds are made up of hydrogen and carbon. So hydrogen is measurely found in the form of hydrocarbons in the combine state. It is also found in protein molecules. So this is how hydrogen occure in the free state as well as in the combine state and there is one more important combined state of hydrogen and that is water, so we get hydrogen in the form of water 2, where hydrogen is combined with oxygen. So finally we know that who discovered hydrogen and how is hydrogen occurring in the atmosphere.