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5. Three fundamental particles of an atom are: Electrons, protons and neutrons
6. Valance Shell: It is the outermost shell of an atom, where the outermost electrons are present that involve in bonding
Radioactivity: It is the spontaneous emission of radiation in the form of particles or high energy photons resulting from a nuclear reaction. A substance that contains unstable atomic nuclei is considered to be radioactive
Atomic mass: It is the mass of the atom, i.e., the mass of the protons and neutrons combined
Nucleons: They are the constituents of the atom's nucleus, i.e., protons and neutrons
Electronic configuration: It is the representation of the arrangement of electrons distributed among the orbital shells and sub-shells
7. Dalton's main 5 postulates:
Five main points of Dalton's atomic theory
1. Elements are made of extremely small particles called atoms.
2. Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.
3. Atoms cannot be subdivided, created, or destroyed.
4. Atoms of different elements combine in simple whole-number ratios to form chemical compounds.
5. In chemical reactions, atoms are combined, separated, or rearranged
8 a) The atom has a nucleus at its centre and the whole mass is concentrated at it centre. Also, The nucleus has a positive charge
b) The main drawback of Rutherford's atomic model is: His atomic model failed to explain about the stability of electrons in a circular path. As per Rutherford's model, electrons revolve around the nucleus in a circular path. But, the electrons will lose energy and fall into the nucleus. And this leads to the instability of the atom.
9. The observations made by Rutherford were: A major fraction of the α-particles bombarded towards the gold sheet passed through it without any deflection, and hence most of the space in an atom is empty.
10. Mass Number of Ne= 20
no. of neutrons= 20-10 = 10
electronic configuration= 1s² 2s² 2p⁶ (or) 2, 8 (in k and l shells)
Mass no. of Mg = 24
no. of neutrons= 24-12= 12
electronic configuration= 1s² 2s² 2p⁶ 3s² (or) 2, 8, 2
Mass no. of Cl= 35
No. of neutrons= 35-17 = 18
electronic configuration= 1s² 2s² 2p⁶ 3s² 3p⁵ (or) 2, 8, 7
Mass no. of K= 39
No. of neutrons= 39-19= 20
electronic configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s²
please refer to the attachment for their structures
11. a) Isotopes are elements that have same atomic number but different mass number. The existence of isotopes because he said all atoms of a given element are identical have the same mass size and chemical properties.
b) variable valency is the phenomenon of atoms that tend to form both positive and negative charges
eg HCl, Cl has negative charge, in Cl₂O₇ is has positive charge. Chlorine can obtain -1, +3, +5 and +7 oxidation states
and Sulphur, It can attain -2, +2, +4 and +6 oxidation states
12. Since the atomic number is similar to the number of electrons, there are 11 electrons in Na atom and there are 23 - 11 = 12 protons in Na atom
13. please refer the second attachment
14. The rule is also known as Aufbau's principle
electrons orbiting one or more atoms fill the lowest available energy levels before filling higher levels (e.g., 1s before 2s).
15. Atomic number = no. of protons= 4
mass number = No. of protons + no of neutrons = 5 + 4 = 9
16. They differ by the mass and no. of neutrons in them. Protium= no neutron and mass no= 1
Deutrium: mass number= 2 and contains one neutron
Tritium: mass number= 3 and contains 2 neutrons also is radioactive
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