Hydrogen

 Hydrogen is the lightest element. It is by far the most abundant element in the universe and makes up about about 90% of the universe by weight. Hydrogen as water (H₂O) is absolutely essential to life and it is present in all organic compounds. Hydrogen is the lightest gas. Hydrogen gas was used in lighter-than-air balloons for transport but is far too dangerous because of the fire risk (Hindenburg). It burns in air to form only water as waste product and if Hydrogen could be made on sufficient scale from other than fossil fuels then there might be a possibility of a Hydrogen economy.

Note that while normally shown at the top of the Group 1 elements in the periodic table, the term "alkaline metal" refers only to Group 1 elements from lithium onwards.

Table: Information About Hydrogen

Name: Hydrogen Symbol: H Atomic number: 1 Atomic weight: 1.00794 (7)  Standard state: gas at 298 K CAS Registry ID: 1333-74-0

Group in periodic table: 1 Group name: (none) Period in periodic table: 1 Block in periodic table: s-block Colour: colourless Classification: Non-metallic

Isolation: In the laboratory, the small amounts of hydrogen gas may be made by the reaction of calcium hydride with water.

CaH₂ + 2H₂O → Ca(OH)₂ + 2H₂

This is quite efficient in the sense that 50% of the hydrogen produced comes from water. Another very convenient laboratory scale experiment follows Boyle's early synthesis, the reaction of iron filings with dilute sulphuric acid.

Fe + H₂SO₄ → FeSO₄ + H₂

There are many industrial methods for the production of hydrogen and that used will depend upon local factors such as the quantity required and the raw materials to hand. Two processes in use involve heating coke with steam in the water gas shift reaction or hydrocarbons such as methane with steam.

CH₄ + H₂O (1100°C) → CO + 3H₂

C(coke) + H₂O (1000°C) → CO + H₂

In both these cases, further hydrogen may be made by passing the CO and steam over hot (400°C) iron oxide or cobalt oxide.

CO + H₂O → CO₂ + H₂

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IUPAC Nomenclature of Organic Compounds Introduction

Study Material for Class XI, Chemistry, Organic Chemistry is available for all. Download  it for free. 
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Quantum Number : XI CBSE

Chemistry is mostly the study of electron interactions between atoms and molecules. Understanding the behavior of the electrons in an atom is an important part of understanding chemical reactions. Early atomic theories used the idea that an atom's electron followed the same rules as a mini solar system where the planets were electrons orbiting a center proton sun. Electric attractive forces are much stronger than gravitational forces, but follow the same basic inverse square rules for distance. Early observations showed the electrons were moving more like a cloud surrounding the nucleus rather than an individual planet. The shape of the cloud, or orbital, depended on the amount of energy, angular momentum and magnetic moment of the individual electron. The properties of an atom's electron configuration are described by four quantum numbers: n, l, m, and s.

The first is the energy level quantum number, n. In an orbit, lower energy orbits are close to the source of attraction. The more energy you give a body in orbit, the further 'out' it goes. If you give the body enough energy, it will leave the system entirely. The same is true for an electron orbital. Higher values of n mean more energy for the electron and the corresponding radius of the electron cloud or orbital is further away from the nucleus. Values of n start at 1 and go up by integer amounts. The higher the value of n, the closer the corresponding energy levels are to each other. If enough energy is added to the electron, it will leave the atom and leave a positive ion behind.

The second quantum number is the angular quantum number, l. Each value of n has multiple values of l ranging in values from 0 to (n-1).This quantum number determines the 'shape' of the electron cloud. In chemistry, there are names for each values of l. The first value, l = 0 called an s orbital. s orbitals are spherical, centered on the nucleus. The second, l = 1 is called a p orbital. p orbitals are usually polar and form a teardrop petal shape with the point towards the nucleus. l = 2 orbital is called a d orbital. These orbitals are similar to the p orbital shape, but with more 'petals' like a clover leaf. They can also have ring shapes around the base of the petals. The next orbital, l=3 is called an f orbital. These orbitals tend to look similar to d orbitals, but with even more 'petals'. Higher values of l have names that follow in alphabetical order.

The third quantum number is the magnetic quantum number, m. These numbers were first discovered in spectroscopy when the gaseous elements were exposed to a magnetic field. The spectral line corresponding to a particular orbit would split into multiple lines when a magnetic field would be introduced across the gas. The number of split lines would be related to the angular quantum number. This relationship shows for every value of l, a corresponding set of values of m ranging from -l to l is found. This number determines the orbital's orientation in space. For example, p orbitals correspond to l=1, can have m values of -1,0,1. This would represent three different orientations in space for the twin petals of the p orbital shape. They are usually defined to be p_x, p_y, p_z to represent the axes they align with.

The fourth quantum number is the spin quantum number, s. There are only two values fors, +½ and -½. These are also referred to as 'spin up' and 'spin down'. This number is used to explain behavior of individual electrons as if they were spinning in a clockwise or counterclockwise. The important part to orbitals is the fact that each value of m has two electrons and needed a way to distinguish them from one another.

These four numbers, n, l, m and s can be used to describe any electron in a stable atom. Each electron's quantum numbers are unique and cannot be shared by another electron in that atom. This property is called the Pauli Exclusion Principle. A stable atom has as many electrons as it does protons. The rules the electrons follow to orient themselves around their atom are simple once the rules governing the quantum numbers are understood.

Atomic Theory: An Overview.

In chemistry and physics, atomic theory is a theory of the nature of matter, which states that matter is composed of discrete units called atoms, as opposed to the obsolete notion that matter could be divided into any arbitrarily small quantity. It began as a philosophical concept in ancient Greece and India and entered the scientific mainstream in the early 19th century when discoveries in the field of chemistry showed that matter did indeed behave as if it were made up particles.
The name "atom" (from the Greek word atomos, which means "indivisible"[1]) was attributed to the basic particle that constituted a chemical element, because the chemists of the era believed that these were the fundamental particles of matter. However, around the turn of the 20th century, through various experiments with electromagnetism and radioactivity, physicists discovered that the so-called "indivisible atom" was actually a conglomerate of various subatomic particles (chiefly, electrons, protons and neutrons) which can exist separately from each other. In fact, in certain extreme environments such as neutron stars, extreme temperature and pressure prevents atoms from existing at all. The field of science which studies subatomic particles is particle physics, and it is in this field that physicists hope to discover the true fundamental nature of matter.
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