Summary

1.    Dalton in 1808 published his work under the name Dalton's Atomic Theory.

2.    The fundamental particles in an atom are electrons, protons and neutrons. Electrons are negatively charged particles, protons are positively charged particles and neutrons are neutral particles.

3.    Protons and neutrons are found in the nucleus of an atom. Electrons move around the nucleus in regions called shells or energy levels.

4.    The atomic number of an element is the number of protons in the nucleus of an atom; it determines the identity of an element.

5.    The mass number is the sum of the number of protons and the number of neutrons in the nucleus.

6.    Isotopes are atoms of same element that have the same atomic number' (number of protons) but different number of neutrons.

7.    Substances which give off invisible rays that affect photographic plates in the same way as light does are called radio-active substances and the phenomenon is termed as Radio-activity. The radiation from Radioactive, substances are of three types (a) Alpha particles or helium nuclei (b) Beta particles or electrons and (c) gamma rays or high energy x-rays.

8.    According to Rutherford atomic model, an atom consists of small dense, and positively "charged centre, called nucleus, which is surrounded by electrons at relatively greater distance from it.

9.    Neil Bohr proposed a model of the atom in which the electrons in a hydrogen atom moves around the nucleus in fixed orbits. The line spectrum is only produced when an electron jumps from higher orbit to lower orbit.

10. An electronic configuration is a particular distribution of electrons among the different shells of an atom.

 

 
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