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STRUCTURE OF ATOM,[object Object]

Outline,[object Object],What is Atom ?,[object Object],The Structure of Atom,[object Object],Thomson’s Model,[object Object],Rutherford’s Model,[object Object],Bohr’s Model of Atom,[object Object],Valency,[object Object],Atomic Number & Mass Number,[object Object]

What is Atom,[object Object],Atom is a basic unit of matter,[object Object],Atom makes one element different from another,[object Object],Atom comes from the Greek word “átomos”, which means uncuttable, or indivisible (Dalton’s Law),[object Object]

Structure of Atom,[object Object],Discovery of two fundamental particles –,[object Object],Electrons & Protons,[object Object],Protons – Positively Charged ions,[object Object],Electrons – Negatively Charged ions,[object Object],Failure of Dalton’s atomic theory (Atom’s are indivisible),[object Object],Three models for structure of Atom,[object Object]

Thompson's Model Of An Atom,[object Object],Thompson proposed-,[object Object], Model of an atom to be similar to that of Christmas pudding. The electrons, in a sphere of positive charge, were like dry fruits in a spherical Christmas pudding.,[object Object],Positive Sphere,[object Object],Electron,[object Object],He thus proposed that-,[object Object],(i) An atom consists of a positively charged sphere and the electrons are embedded in it.,[object Object],(ii) The negative and positive charges of an atom are equal in magnitude. So, the atom as whole is electrically neutral.,[object Object]

Rutherford's Model of an Atom ,[object Object],Observation:,[object Object],Conclusion:,[object Object],Experiment: ,[object Object],Rutherford selected a gold foil as thinner layer as possible (nearly about 1000 Atoms thick),[object Object],He selected Alpha particles which are doubly charged HELIUM ion.,[object Object],It was expected that Alpha particles could be deflected by the sub-atomic particles in the gold atoms, as alpha particles were much heavier than proton. He did not expected to see a large deflection.,[object Object],Most of the space inside the atom is empty because most of the alpha particles passed through without getting deflected.,[object Object],Very few particles were deflected from their path indicating that positive charge of the atom occupies very little space.,[object Object],There is positively charged centre in an atom called nucleus in well define orbits. ,[object Object],The size of the nucleus is very small as compare to size of atoms.,[object Object],Most of the fast moving alpha particles past straight through the gold foil.,[object Object],Some of the alpha particles were deflected by the foil by small angles.,[object Object],Surprisingly 1 out of every 12000 particles appear to rebound. ,[object Object],The gold foil experiment was conducted under the supervision of Rutherford at the University of Manchester in 1909 by scientist Hans Geiger and undergraduate student Ernest Marsden. Rutherford, chair of the Manchester physics department at the time of the experiment, is given primary credit for the experiment, as the theories that resulted are primarily his work. Rutherford's gold foil experiment is also sometimes referred to as the Geiger-Marsden experiment.,[object Object]

Bohr's Model Of Atom,[object Object],Nucleus,[object Object],K shell,[object Object],L Shell,[object Object],M Shell,[object Object],In order to overcome the objection raised against Rutherford’s model of the atom, Neil Bohr put forward the following postulates about the model of the atom- ,[object Object],Only certain special orbit known as discrete orbit of an electron, are allowed inside an atom.,[object Object],(ii) While revolving in discrete orbits the electrons do not radiate energy.,[object Object]

Model of Hydrogen Atom,[object Object],Structure of AtomsDistribution of Electrons,[object Object],Model of Atom,[object Object]

Valency,[object Object],Is the Combining Capacity of an Element,[object Object],Determines how the atoms of one element combines with the atoms of another or same element to form a chemical compound,[object Object],Depends on the how the electrons are arranged in the outermost shell,[object Object],Bohr-Bury Scheme – Outermost shell of an atom can accommodate a max of 8 electrons,[object Object],Is either equal to the number of electrons in the outermost shell or number of electrons required to complete 8 electrons in the outermost shell,[object Object]

Valency of Some Elements,[object Object]

ATOMIC NUMBER,[object Object],Atomic number defined as the total number of protons present in the nucleus of an atom. It is denoted by Z.,[object Object],Atomic number of ,[object Object], Carbon is 6 because it has 6 protons in its nucleus.,[object Object],MASS NUMBER,[object Object],Atomic Notation,[object Object],Mass number defined as the sum of total number of protons and nucleons present in the nucleus of an atom. It is denoted by A.,[object Object],Mass number of nitrogen is 14 because it has 7 protons and 7 neutrons in its nucleus.,[object Object],In the notation for an atom, the atomic number, mass number and the symbol of the element are to be written as:,[object Object],Nitrogen atom,[object Object]

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