Hydrogen and Helium

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HELIUM

CONTENTS

INTRODUCTION………………….….……………………

PROPERTIES……………………………….………………

OCCURRENCE……………………………………………

USES………………..………………………………………

BIBLIOGRAPHY……...……………………………………

INTRODUCTION

Heliums name comes from the Greek word “helios”, meaning sun. Helium is odourless and colourless and remains as a gas at room temperature; this chemical element is abbreviated as He. Helium has two protons in its nucleus whereas the atomic number of helium is 2 and is listed in group VIII of the periodic table. As a noble gas helium is almost chemically inert, unreactive. After hydrogen, helium is the most abundant element in the universe.

During an eclipse in 1868, French astronomer Pierre Janssen discovered helium. After Helium was proven to be an element it was named by a British chemist Sir Edward Frankland and British astronomer Sir Joseph Norman Lockyer. British chemist Sir William Ramsay, who discovered it in cleveite mineral containing uranium, isolated the gas from the outside world in 1895. Later in 1907 British physicist Sir Ernest Rutherford showed that the nuclei of the helium atoms contained positively charged nuclear particles also known as alpha particles.

PROPERTIES

Besides hydrogen, helium is the lightest of all gases. The atomic weight of helium is 4.0026. In phase helium I: Helium becomes a liquid at -268.9°C, phase helium II: below -270.98°C becomes a superfluid. Helium becomes solid at -272.2°C at pressures above 26 atmospheres, helium boils at -268.9°C and has a density of 0.1664 g/litre at 20°C and one atmosphere.

The stable isotopes of helium are a rare form of helium-3 and the most common form of helium-4. Isotopes from helium-5 to helium-10 are unstable and rapidly decay, these are only known from certain nuclear reactions and experiments with particle accelerators. Because helium’s’ electron shell is always full, making reactions with other elements is difficult and the resulting compounds would be unstable. However it is possible for some chemical reactions to occur under extreme pressure. Molecules of compounds with neon, and hydrogen have been spotted and other compounds have been suggested, like the combination of hydrogen, helium and iron. Due to helium’s abundance in the universe, such reactions existence, although rare - is important in Cosmology, study of the universe. Helium is found to be most difficult of all gases to liquefy and impossible to solidify at atmospheric pressure. Because of these properties, it is extremely useful for experimental work in producing and measuring temperatures close to absolute zero. It’s possible to cool helium close to absolute zero at normal pressure via removing vapour above the liquid. At a temperature a little above absolute zero super fluid helium, it’s transformed into a liquid with unique physical properties believed to result from quantum mechanical effects (description of particles that make up matter). This has no freezing point, and thickness is zero; passes through minute cracks and pores, and even sneaks up sides and over the lip of a container. Helium-3 has different properties when liquefied. Helium acts like a solid when it is cooled to near absolute zero. Some experiments show that at low temperatures solid helium has unusual properties that offer a possible new state of matter called super solidity. Scientists are still investigating the existence of super solidity. Helium when solid becomes rigid in a super solid position, but also show features of continuous flow similar to super fluidity.

OCCURRENCE
Helium makes up 9% of the universes atoms, where as hydrogen makes about 90%. Helium also makes 25% of the mass of the universe, hydrogen-73% and other heavier elements make up the remaining amounts. It is believed that following the big bang the event that began life, most of helium in the universe was created 13.7 billion years ago. The helium from then exists as gas in space and in stars. This helium...
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