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SS1: CHEMISTRY - 1ST TERM

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

In Covalent Molecules, atoms combine by sharing electrons.

Covalent molecules have a definite shape due to the fact that Covalent bonds are rigid and highly directional. But the Ionic bonds are not directional. Shapes of Covalent molecules are as follows:

1. Linear Shape

All diatomic molecules are Linear in shape e.g. H2, Cl2, O2, N2. Other Compounds that have a Linear shape are CO, HCl, HF, CO2, SO2, etc. A linear molecule is a molecule in which atoms are deployed in a straight line, and the bond angle is 180°C.

The Linear shape of Hydrogen, Oxygen, Nitrogen, and Chloride

(a) Hydrogen (H2)

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Single Covalent bond

(b) Oxygen (O2)

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Double Covalent bond

(c) Nitrogen (N2)

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Triple Covalent bond

 (d) Chloride (Cl2)

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Single Covalent bond

2. Tetrahedral Shape

This is a molecular shape that results when there are four bonds and no lone pairs around the central atom in a molecule. The atoms bonded to the central atom lie at the corners of a tetrahedron with a 109.5° angle between them.

The Covalent molecules that are tetrahedral in shape are methane (CH4), Tetrachloromethane (CCl4), Silicon tetrachloride (SiCl4), etc.

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Tetrahedral shape of a methane molecule

3. Angular Shape

Angular Shape is also called V-Shape. Water is the only covalent molecule that has an angular shape. The bond angle in water is 105°. A molecule of water has two pairs and two lone pairs of electrons. In a water molecule, the central atom is Oxygen 

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 The angular shape of the water

4. Trigonal Shape

Trigonal molecular shape results when there are three bonds around the central atom in a molecule. The bond angles are 120°.    

There are two types of Trigonal Shape

1. Trigonal Pyramidal Shape

2. Trigonal Planar Shape

1. Trigonal Pyramidal Shape

Trigonal pyramidal shape results when there are three bonds and one lone pair of electrons on the central atom in the molecule e.g. Ammonia (NH3) and Phosphine (PH3). In the Ammonia molecule, the three hydrogen atoms occupy the corners of the triangular base, with the lone pair of electrons occupying a large space at the apex. The bond angle between the two N-H bonds is approximately 107°.

Screen Shot 2021 01 17 at 6.10.31 PM Easy Resize.com 1

2. Trigonal Planar Shape

Trigonal Planar Shape results when a molecule has a central atom bonded to three surrounding atoms with no lone pair of electrons e.g. Phosphorus Chloride (PCl3), Aluminium Chloride (AlCl3), Boron trifluoride (BF3), Aluminium trihydride (AlH3), Sulphur (VI) Oxide (SO3), etc.

Theory Questions

1. (a) List two forces of attraction that can exist between covalent molecules

(b) Name the type of Intermolecular force of attraction in the following:

(i) Iodine Crystals 

(ii) Hydrogen Fluoride 

(iii) Argon

View Answer

2. (a) Give the reason why Hydrogen Fluoride is a liquid at room temperature, unlike Hydrogen Chloride

(b) Name the types of bonds within a water molecule and between water molecules.

View Answer

3. (a) Explain the term Metallic Bonding

(b) State the type of chemical bond between Aluminium atoms in a sheet of Aluminium

(c) Mention three physical properties of Metal

View Answer

4. Give two examples of each of the following Covalent molecules 

(a) Linear Shape – O2, HCl

(b) Tetrahedral Shape – CH4, SiCl4

(c) Trigonal Shape – NH3, SO3

(d) Trigonal Planar Shape – SO3, AlCl3

View Answer

5. (a) Given the boiling points of the following Hydrid     

Hydride   Boiling Point  
H2O  100°c
H2S-65°c 
HF20°c
HCl-85°c

State what is responsible for the high boiling point of H2O and HF

(b)Explain the following observations 

(i) Mg has a higher melting point than Na

 (ii) K is a better reducing agent than Na

View Answer

Theory Question 1

1. (a) List two forces of attraction that can exist between covalent molecules

i) Metalic bonding
ii) Intermolecular forces

(b) Name the type of Intermolecular force of attraction in the following:

(i) Iodine CrystalsVander Waals forces

(ii) Hydrogen Fluoride Hydrogen bond

(iii) ArgonVander Waals forces

Theory Question 2

2. (a) Give the reason why Hydrogen Fluoride is a liquid at room temperature, unlike Hydrogen Chloride

AnswerThis is attributed to the presence of hydrogen bonding in Hydrogen Fluoride as compared to Hydrogen chloride.

(b) Name the types of bonds within a water molecule and between water molecules.

Answer – Hydrogen bond

Theory Question 3

3. (a) Explain the term Metallic Bonding

AnswerMetallic bonding is the force that holds atoms together in a metal.

(b) State the type of chemical bond between Aluminium atoms in a sheet of Aluminium

Answer – Metallic bond

(c) Mention three physical properties of Metal

Theory Question 4

4. Give two examples of each of the following Covalent molecules 

(a) Linear Shape – O2, HCl

(b) Tetrahedral Shape – CH4, SiCl4

(c) Trigonal Shape – NH3, SO3

(d) Trigonal Planar Shape – SO3, AlCl3

Theory Question 5

5. (a) Given the boiling points of the following Hybrid     

Hydride   Boiling Point  
    H2O  1000c
    H2S-650
  HF200c
  HCl-850c

State what is responsible for the high boiling point of H2O and HF

AnswerThis is as a result of the presence of hydrogen bonding in these molecules.

(b)Explain the following observations 

(i) Mg has a higher melting point than Na

Answer – Magnesium shares two valence electrons in an electron cloud while sodium shares one. This suggests that magnesium has a stronger metallic bond than sodium. Hence, breaking the metallic bond in magnesium will require more energy; when compared to sodium. Thus, magnesium has a higher melting point than sodium.

 (ii) K is a better reducing agent than Na

Answer –  This is because potassium is far more reactive than sodium. Hence, a better reducing agent.

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