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SS1: CHEMISTRY - 1ST TERM

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  1. Introduction to Chemistry and Laboratory Apparatus | Week 1
    5 Topics
    |
    1 Quiz
  2. Nature of Matter | Week 2
    3 Topics
    |
    1 Quiz
  3. Separation Techniques I | Week 3
    1 Topic
  4. Separation Techniques II | Week 4
    5 Topics
    |
    1 Quiz
  5. Particulate Nature of Matter I | Week 5
    5 Topics
    |
    1 Quiz
  6. Particulate Nature of Matter II | Week 6
    9 Topics
    |
    1 Quiz
  7. Symbols, Formulae & Oxidation Number | Week 7
    7 Topics
    |
    1 Quiz
  8. Laws of Chemical Combination | Week 8
    4 Topics
    |
    1 Quiz
  9. Chemical Equation & Chemical Combination (Chemical Bonding) I | Week 9
    4 Topics
    |
    1 Quiz
  10. Chemical Combination (Chemical Bonding) II | Week 10
    4 Topics
    |
    1 Quiz
  11. Chemical Combination (Chemical Bonding) III & Shapes of Covalent Molecules | Week 11
    3 Topics
    |
    1 Quiz

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Topic Content:

  • Arrangement of Particles in an Atom
  • Energy Levels and Maximum Number of Electrons
  • Electronic configuration of the 1st 20 Elements
  • Theory Questions

In 1913, a scientist Niels Bohr forwarded his own model of the atom based on the quantum mechanics originally developed by Planck.

He proposed that the model of an atom consists of an extranuclear part known as an electron which is located in spherical orbits (shell) around the nucleus. The orbit/energy level is designated by Letters ( K, L, M, N). These labels correspond to the principal quantum numbers 1, 2, 3, 4… respectively.

bhors atom model

Energy Levels and Maximum Number of Electrons:

 

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Theory Question 1

1. (a) Give two reasons to show that matter exists in form of particles

Answer:

Osmosis – This is the movement of water molecules from a more dilute solution to a more concentrated solution via a semi-permeable membrane. For example, when beans are placed in a glass of water, they would begin to swell after some days. This explains that water molecules are composed of tiny particles.

Dissolution of solid in liquid – This is more evidence that matter exists in the form of particles. When a cube of sugar is dissolved in water, the sugar dissociates into particles which spread within the liquid.

 

(b). Define the following, giving two examples in each case 
(i) Atom (ii) Molecule (iii) Ion

Answer:

(i) An atom is the smallest particle of an element which can take part in a chemical reaction. e.g. Oxygen (O).

(ii) A molecule is the smallest particle of a substance that can normally exist separately and still retain the chemical properties of that substance. e.g. oxygen molecule (O2).

(iii) An ion is any atom or group of atoms which possesses an electric charge. e.g. oxygen (O2+).

Theory Question 2

What are the contributions of the following scientists in the constituents of the atom (i) J.J Thompson (ii) Robert Millikan (iii) Ernest Rutherford (iv) James Chadwick (v) Henry Mosely (vi) Neil Bohr

Answer:

i. J. J. Thompson – Discovery of electron

ii. Robert Millikan – Discovered the charge in neutron via the Millikan oil-drop experiment.

iii. Ernest Rutherford – He proposed the nucleus theory of an atom

iv. James Chadwick – Discovery of neutron

v. Henry Mosely – He suggested that the number of protons in the nucleus is a fundamental characteristic of an atom.

vi. Neil Bohr – He proposed that the model of an atom consists of an extranuclear part called an electron.

Theory Question 3

(a) Name the three particles of an atom, their charges, mass and their position in the atom 

Answer:

Particles Location Charge Mass
Proton Nucleus Positive (+) 1
Electron Shell Negative (-) \(\frac{1}{1840}\)
Neutron Nucleus Nil (Neutral) 1

 

(b) Draw a simple model of an atom

Answer:

bhors atom model

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