Chemical Bonding (Advanced)

CBSE Science. Optional Advanced level: the octet rule, Lewis symbols, shared and lone pairs, incomplete, expanded and odd-electron molecules, the electron sea model. Every sheet has 20 questions in three sections and an answer key, and the numbers change every time.

Open a printable sample sheet Cheat sheet: formulas and key points

Sample questions

Real questions from this chapter, as the app sets them. Tap Answer to see the answer and working.

Section A · multiple choice

1.
How many dots surround the symbol Be in the Lewis symbol of beryllium (atomic number 4)?
1. 4
2. 2
3. 3
4. 6
Answer
(b) 2
configuration 2, 2: 2 valence electrons, one dot each
2.
How many electrons are there in the valence shell of the central silicon atom in SiH₄?
1. 8
2. 6
3. 4
4. 10
Answer
(a) 8
4 shared pairs and 0 lone pairs: 2 × 4 = 8
3.
The total number of valence electrons in one molecule of NH₃ is:
1. 9
2. 7
3. 8
4. 10
Answer
(c) 8
1 × 5 (N) + 3 × 1 (H) = 8

Section B · short answer

4.
For magnesium (atomic number 12), write (a) its electron configuration and (b) the number of dots in its Lewis symbol.
Answer
(a) 2, 8, 2; (b) 2
fill 2, 8, 8 …; the outer shell has 2
5.
How many pairs of electrons are shared between the two nitrogen atoms in N₂?
Answer
3
a triple bond

Section C · long answer

6.
Work out the Lewis structure of BH₃. For the central B atom, find (a) the number of shared pairs, (b) the number of lone pairs and (c) the electrons in its valence shell. (d) Does it obey the octet rule? (Yes or No)
Answer
(a) 3; (b) 0; (c) 6; (d) No
B has 3 valence electrons; 2 × (3 + 0) = 6

Fresh sheets for your child

In the app, every Chemical Bonding (Advanced) sheet is new: the app remembers the questions your child has already had and leaves them out. Print the sheet as a PDF, or use notebook mode and write the answers in a notebook.

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