Question

Based on the VSEPR theory, which of the following would have a tetrahedral arrangement of electrons around the central atom?
a) CH4
b) H2O
c) CO2
d) NH3

Answer 1

Answer:

(A) CH₄ has a tetrahedral arrangement and is therefore correct.

VSEPR Theory:

VSEPR Theory (Valence Shell Electron Pair Repulsion Theory) is a chemical model used to predict the geometry of individual molecules from the number of electron pairs surrounding their central atoms. VSEPR Theory states that:

1. Electron pairs repel each other
2. Electron pairs arrange themselves to minimise repulsion
3. Shapes are determined by number of electron pairs

According to VSEPR Theory,  the tetrahedral arrangement of electrons around the central atom occurs when there are four electron groups around the central atom. Each group can be either a bonding pair or a lone pair of electrons.

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Among the options given:

a) CH₄ (methane) has a tetrahedral arrangement. It has four bonding pairs of electrons around the central carbon atom.

b) H₂O (water) has a bent or angular shape. It has four electron groups, but only two of them are bonding pairs, while the other two are lone pairs, resulting in a bent molecular geometry.

c) CO₂ (carbon dioxide) has a linear arrangement. It has two double bonds, and hence two electron groups around the central carbon atom, resulting in a linear molecular geometry.

d) NH₃ (ammonia) has a trigonal pyramidal arrangement. It has three bonding pairs of electrons and one lone pair around the central nitrogen atom, resulting in a trigonal pyramidal molecular geometry.

Therefore, the correct answer is (A) CH₄.

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