CBSE Class 9 Chemistry-Structure of an Atom (2). Learning the important concepts is very important for every student to get better marks in examinations. The concepts should be clear which will help in faster learning. The attached concepts made as per NCERT and CBSE pattern will help the student to understand the chapter and score better marks in the examinations.
TOPICS OF CHAPTER:-
CHAPTER 2: STRUCTURE OF ATOM:
1. Energy of electron in H-atom, En = -2.18 x 10 -18 / n2 Jatom-1
2. Energy of electron in H-like species atom, En = -2.18 x 10 -18 z2 / n2 Jatom-1
3. Angular momentum of electron, mvr = nh/2π
4. de- Broglies wavelength, λ = h / mv or λ = h / p
5. Plank’s equation E = hϑ
6. Einstein equation , E = mc2
7. Wave number( )=1/ λ = RH[1/n12 – 1/n22]
8. Isotopes: These are the atoms of the same element having the same atomicnumber but different mass number.e g 1H1,1H2,1H3
9. Isobars: Isobars are the atoms of different elements having the same massnumber but different atomic number.
e g 18Ar40 , 20Ca40
10. Isoelectronic species: These are those species which have the same numberof electrons.
11. Electromagnetic spectrum:-It is a continuous spectrum. It consists of a range of electromagnetic radiations arranged in the order of increasing wavelengths or decreasing frequencies.
12. Spectroscopy:-The study of emission or absorption spectra is referred as spectroscopy.
13. o Emission spectrum: The spectrum of radiation emitted by a substance that has absorbed energy is called an emission spectrum.
14. o Absorption spectrum : The spectrum obtained when radiation is passed through a sample of material. The sample absorbs radiation of certain wavelengths. The wavelengths which are absorbed are missing and come as dark lines.
15. Bohr’s model for hydrogen atom:
a. An electron in the hydrogen atom can move around the nucleus in a circular path of fixed radius and energy. These paths are called orbits orenergy levels. These orbits are arranged concentrically around the nucleus.
b. As long as an electron remains in a particular orbit, it does not lose or gain energy and its energy remains constant.
c. When transition occurs between two stationary states that differ in energy, the frequency of the radiation absorbed or emitted can be calculated
d. An electron can move only in those orbits for which its angular momentum is an integral multiple of h/2π The radius of the nth orbit is given by rn =52.9 pm x n2 /Z energy of electron in nth orbit is ;
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