basic chemistry notes and chemistry topics
basic chemistry notes for competitive exams – ELEMENTS, COMPOUNDS, MIXTURES, ATOMIC STRUCTURE, OXIDATION AND REDUCTION.
ELEMENTS — chemistry topics
- An element may be defined as a substance which is made by the same type of atoms and it can neither be broken into nor built from two or more simpler substance by any known physical or chemical methods, e.g., copper, silver, hydrogen, carbon, oxygen, nitrogen, gold, iron etc.
- A compound may be defined as a substance which contains two or more elements combined in some fixed proportion by weight and which can be decomposed into two or more elements by any suitable method.
- The properties of a compound are entirely different from those of the elements from which it is made.
- Some common examples of compounds are water, sugar, salt, aspirin, chloroform, alcohol and ether.
- A material containing two or more elements or compounds in any proportion is a mixture.
- The components of a mixture can be separated by physical means like filtration, sublimation, and distillation.
ATOMIC STRUCTURE – basic chemistry notes
- Atom is the smallest part of the element that takes part in a chemical reaction. The Atom of an element can not is changed into that of another element by a chemical or physical means. It does not exist in the free state.
- A molecule is the smallest part of an element or compound that is capable of existing Independently.
ATOMIC WEIGHT (OR ATOMIC MASS) – chemistry topics
- The atomic mass of an element is the number of times its atom is heavier than 1/12th of the mass of carbon (C12) atom.
- The unit used to measure atomic mass called atomic mass unit, i.e., amu.
- The electron is a fundamental particle of an atom which carries a unit negative charge. It was discovered by J.J. Thomson in 1897.
- It is a fundamental particle of an atom carrying a unit positive charge. It was discovered by Rutherford and Goldstein in 1886.
- It is a fundamental particle of an atom carrying no charge. It was discovered by Chadwick in 1932.
- The atoms of the same element having different mass numbers are called isotopes.
- Elements having the same atomic mass but differ in atomic number are called isobars.
- Elements having the same number of neutrons are called isotones.
OXIDATION AND REDUCTION – basic chemistry notes
- Oxidation is a process in which a substance adds on oxygen or hydrogen. In modern terms, oxidation is the process in which a substance loses electrons.
- The reduction is a process in which a substance adds on hydrogen or loses oxygen. In modern terms, a reduction is a process in which a substance gains electrons.
- Oxidation and reduction always occur simultaneously. If one substance is oxidized, another is reduced. The reaction in which this oxidation-reduction process occurs is called a redox reaction.
- Oxidizing agents are substances which bring about the oxidation of other substances, e.g., Potassium Permanganate, Potassium Dichromate, Nitric Acid, Hydrogen Peroxide, etc.
- Reducing agents are substances which bring about the reduction of other substances, e.g., hydrogen sulfide, hydrogen, carbon, sulfur dioxide, etc.
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