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Delhi

Essentials Of Chemistry

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Published in: Chemistry
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Descriptions of matter, element, atom, molecule, atomic mass, atomic number, anions, cations, atomicity etc. 

Chandrasekhar / Hyderabad

10 years of teaching experience

Qualification: M.Sc, B.Sc

Teaches: Mathematics, Physics, All Subjects

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  1. 1 ESSENTIALS OF CHEMISTRY MATTER, ITS MASS, PARTICLES , ATOMS, MOLECULES, SUBSTANCES, ATOMIC MODEL, POSTULATES , ELECTRONS, PROTONS, NEUTRONS, ORBITS , VALENCY ETC. WE SEE A LARGE VARIETY OF THINGS AROUND US , WHICH HAVE DEFINITE SHAPE ,SIZE AND MASS. ANYTHING WHICH HAS MASS AND OCCUPIES SPACE IS CALLED MATTER. MASS IS THE QUANTITY OF MATTER IN A GIVEN SAMPLE. MATTER CONSISTS OF LARGE NO OF VERY SMALL PARTICLES , CALLED ATOMS. ELEMENTS ARE MADE UP OF ATOMS. EACH ELEMENT IS CHARACTERIZED BY MASS OF ITS ATOMS. THE PHENOMENON OF CHANGE OF MATTER FROM ONE PHYSICAL STATE TO ANOTHER PHYSICAL STATE AND BACK TO ITS ORIGINAL STATE BY ALTERING THE CONDITIONS OF TEMPERATURE AND PRESSURE , IS CALLED INTER CONVERSION OF MATTER EG. LIQUID CONVERTING TO ICE AND ICE CONVERTING BACK TO LIQUID MATTER GENERALLY IS IN THE FORM OF SOLIDS, LIQUID S AND GASES.. SOLIDS HAVE DEFINITE SHAPE AND VOLUME, LIQUIDS HAVE INDEFINITE SHAPE BUT DEFINITE VOLUME, GASES HAVE INDEFINITE SHAPE AND VOLUME. MELTING : THE PROCESS OF CONVERSION OF SOLID INTO LIQUID BY ABSORBING HEAT ENERGY IS CALLED MELTING. EX. CONVERSION OF ICE INTO WATER. MELTING POINT : THE TEMPERATURE AT WHICH A SOLID CONVERTS INTO LIQUID IS CALLED MELTING POINT. MELTING POINT OF ICE IS 00 C AT latm PRESSURE.
  2. 2 FREEZING: THE PROCESS OF CONVERSION OF LIQUID INTO SOLID BY RELEASING HEAT ENERGY IS CALLED FREEZING. EX. CONVERSION OF WATER INTO ICE. FREEZING POINT : THE TEMP AT WHICH A LIQUID CONVERTS INTO SOLID IS CALLED FREEZING POINT. THE FREEZING POINT OF WATER IS 00 CAT latm PRESSURE. BOILING: THE PROCESS OF CONVERSION OF LIQUID INTO GAS BY ABSORBING HEAT ENERGY IS CALLED BOILING. EX . CONVERSION OF WATER INTO WATER VAPOUR. BOILING POINT: THE TEMPERATURE AT WHICH A LIQUID CONVERTS INTO GAS IS CALLED BOILING POINT. EX. THE BOILING POINT OF WATER IS 1000 c AT latm PRESSURE ATOMS IN A MATTER OR ELEMENT ARE FURTHER SUBDIVIDED INTO 3 SUB ATOMIC PARTICLES NAMELY, ELECTRON,PROTON AND NEUTRON. ELECTRON WAS DISCOVERED BY JJ THOMPSON. IT IS A NEGATIVELY CHARGED PARTICLE. THE CHARGE OF ELECTRON IS -1.602X10-19c. MASS OF ELECTRON IS 9.1XIO-31KG OR .00055 amu PROTON WAS DISCOVERED BY GOLDSTEIN. IT IS A POSITIVELY CHARGED PARTICLE. THE CHARGE OF PROTON IS 1.602X10-19c. MASS OF PROTON IS 1.672XIO-27KG OR 1.0072 amu NEUTRON WAS DISCOVERED BY JAMES CHADWICK. IT IS NEUTRAL. IT HAS NO CHARGE. MASS OF NEUTRON IS 1.675X10 27KG OR 1.0086 amu AN ATOM ESSENTIALLY CONTAINS 2 PARTS. NUCLEAR PART , WHICH CONTAINS PROTONS AND NEUTRONS , EXTRA NUCLEAR PART THAT CONTAINS ELECTRONS REVOLVING ROUND THE NUCLEUS IN AN ORBIT. TOTAL MASS OF ATOM IS CONCENTRATED AT THE CENTRE. PROTON AND NEUTRON ARE CALLED AS NUCLEONS. THE NUCLEUS OF AN ATOM IS POSITIVE LY CHARGED BECAUSE OF THE PRESENCE OF PROTONS AND ATOM AS A WHOLE IS NEUTRAL BECAUSE OF THE PRESENCE OF ELECTRONS AROUND THE NUCLEUS WHICH ARE EQUAL TO NO., OF PROTONS INSIDE THE NUCLEUS. ATOMIC NO IS z=N0. OF PROTONS = NO. OF ELECTRONS.
  3. 3 ATOMIC MASS = A = NO. OF PROTONS + NO. OF NEUTRONS = Z+N NO OF NEUTRONS = A Z THE ELECTRONS ARE REVOLVING AROUND THE NUCLEUS IN SPECIFIC ORBITS OR SHELLS WITH HIGH SPEEDS. THESE ARE DENOTED BY OR 1 2 3 4 THE ORBITS OF ELECTRONS AROUND THE NUCLEUS OF AN ATOM THE ARRANGEMENT OF ELECTRONS IN VARIOUS SHELLS OF AN ATOM OF AN ELEMENT IS CALLED ELECTRONIC CONFIGURATION. THE INCREASING ORDER OF ENERGIES OF VARIOUS SHELLS IS ELECTRONS OCCUPY LOWER ENERGY LEVEL FIRST.
  4. 4 THE MAX NO. OF ELECTRONS PRESENT IN A SHELL OF AN ATOM OF AN ELEMENT IS 2n2. WHERE n IS THE ORBIT NO. OR SHELL NO. K HAS 2 ELECTRONS, L HAS 8 ELECTRONS , M HAS 18 ELECTRONS ETC. THE LAST SHELL OF AN ATOM THAT CONTAINS ELECTRONS IS CALLED OUTERMOST SHELL OR VALENCE SHELL. THE ELECTRONS PRESENT IN VALENCE SHELL ARE CALLED VALENCE ELECTRONS . ATOMS WHICH HAVE SAME ATOMIC NO BUT DIFFERENT MASS NO ARE CALLED AS ISOTOPES.. EX : IH ,1H3 ATOMS OF DIFFERENT ELEMENTS HAVING SAME MASS NUMBER BUT DIFFERENT ATOMIC NO ARE CALLED ISOBARS. EX: 18Ar40,20Ca40 ATOMS OF DIFFERENT ELEMENTS HAVING SAME NO OF NEUTRONS ARE CALLED ISOTONES. EX: 9F19,10Ne20 MOLECULE : THE UNIT OF MATTER THAT RESULTS WHEN 2 OR MORE ATOMS ARE JOINED TOGETHER IS CALLED MOLECULE. MOLECULES ARE MADE UP OF ATOMS OF SAME OR DIFFERENT ELEMENTS. MOLECULES ARE REPRESENTED BY A CHEMICAL FORMULA . THUS CHEMICAL FORMULA TELLS NO. OF ATOMS OF VARIOUS ELEMENTS PRESENT IN THE MOLECULE. EX: 1-12, 1-120, NH3 HCL IH IS ONE H ATOM, 11-12 IS ONE HYDROGEN MOLECULE. 2NH3 IS 2 AMMONIA MOLECULES. ATOMICITY : NO. OF ATOMS PRESENT IN A MOLECULE OF AN ELEMENT IS CALLED ITS ATOMICITY. EX 02 ATOMICITY OF OXYGEN MOLECULE IS 2 AS IT CONTAINS 2 ATOMS OF OXYGEN IN OXYGEN MOLECULE.
  5. 5 HOMO ATOMIC MOLECULES MOLECULES WHICH ARE MADE UP OF ATOMS OF SAME ELEMENT ARE CALLED HOMO ATOMIC MOLECULES. EX. 1-12 02, P4 HETERO ATOMIC MOLECULES MOLECULES WHICH ARE MADE UP OF ATOMS OF DIFFERENT ELEMENTS ARE CALLED HETERO ATOMIC MOLECULES. EX. HCL, NaCl, 1-120 IONS OR RADICALS AN ATOM OR GROUP OF ATOMS OF SAME OR DIFFERENT ELEMENTS HAVING POSITIVE OR NEGATIVE CHARGE IS CALLED ION OR RADICAL. IONS CAN BE CLASSIFIED INTO TWO TYPES DEPENDING ON THE NATURE OF CHARGE PRESENT ON THEM. CATION : AN ATOM OR GROUP OF ATOMS WHICH HAS POSITIVE CHARGE IS CALLED CATION OR ELECTROPOSITIVE ION. WHEN ONE OR MORE ELECTRONS ARE REMOVED FROM AN ATOM OR A MOLECULE THEN IT LEADS TO THE FORMATION OF CATION.THE POSITIVE CHARGE ON THE CATION IS EQUAL TO THE NO. OF ELECTRONS REMOVED DURING ITS FORMATION. EX. Na ATOM LOSES AN ELECTRON TO BECOME SODIUM ION. Na+ Na+ (2,8 11p,10e) + lip,lle) (loss of electron) le- ANION : AN ATOM OR GROUP OF ATOMS WHICH HAS NEGATIVE CHARGE IS CALLED ANION OR ELECTRONEGATIVE ION. WHEN ONE OR MORE ELECTRONS ARE ADDED TO AN ATOM OR A MOLECULE THEN IT LEADS TO THE FORMATION OF ANION.THE NEGATIVE CHARGE ON THE ANION IS EQUAL TO THE NO. OF ELECTRONS ADDED DURING ITS FORMATION. EX. CHLORINE GAINS ONE ELECTRON TO BECOME CHLORIDE ION Cl- CI(2,8,7 17p,17e) + (gain of electron) le- 17p,18e)
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