Some Basic Concepts of Chemistry

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Hydrogen

 

1. Hydrogen is the lightest element known since it has an atomic mass of 1.0079
2. Hydrogen resembles Group 1 elements because it has electronic configuration (1s1) similar to alkali metals and can loose one electron to form unipositive ions
3. Hydrogen also resembles elements of group 17 (Halogens) because hydrogen just like halogens needs just one electron to acquire the configuration of the nearest noble gas i.e. Helium
4. Hydrogen has three isotopes – Protium, deuterium and tritium

5. In elemental form Hydrogen exists as a diatomic molecule H2 and is called dihydrogen
6. Water gas is name given to the mixture of carbon monoxide and hydrogen. Water gas is also called synthesis gas or syngas
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Redox Reactions

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1. Redox reactions are those reactions in which oxidation and reduction takes place simultaneously
2. Classical view of redox reactions

  •  Oxidation is addition of oxygen / electronegative element to a substance or removal of hydrogen / electropositive element from a substance
  •  Reduction is removal of oxygen / electronegative element from a substance or addition of hydrogen / electropositive element to a substance

3. Redox reactions in terms of Electron transfer

  •  Oxidation is defined as loss of electrons by any species
  •  Reduction is defined as gain of electrons by any species

4. In oxidation reactions there is loss of electrons or increase in positive charge or decrease in negative charge
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Classification of Elements

1. Johann Dobereiner classified elements in group of three elements called triads.
2. In Dobereiner’s triad the atomic weight of the middle element is very close to the arithmetic mean of the other two elements.
3. Dobereiner’s relationship is referred as Law of triads.
4. Since Dobereiner’s Law of triads worked only for few elements, it was dismissed.
5. Chancourtois arranged elements in order of increasing atomic weights and made a cylindrical table of elements.
6. John Newland arranged the elements in the increasing order of atomic weight and noted that the properties of the every eighth element are similar to the first one. This relationship is called as “Law of octaves”
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Chemical Bonding

                                                             Chemical Bonding and Molecular Structure

1. The attractive force which holds together the constituent particles (atoms, ions or molecules) in chemical species is known as chemical bond.
2. Tendency or urge atoms of various elements to attain stable configuration of eight electrons in their valence shell is cause of chemical combination.
3. The principle of attaining a maximum of eight electrons in the valence shell or outermost shell of atoms is known as octet rule.
4. Electronic Theory: Kossel-Lewis approach to chemical Bonding: Atoms achieve stable octet when they are linked by chemical bonds. The atoms do so either by transfer or sharing of valence electrons...

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Atomic Structure

Structure Of Atom

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