The number of sigma and pi bonds in benzene, respectively, is:
- A.12 and 3
- B.3 and 3
- C.6 and 3
- D.9 and 3
Correct answer
Explanation
The correct answer is A, 12 and 3. Benzene has the formula C6H6 and a ring of six carbon atoms, each carrying one hydrogen. Count the sigma bonds first: six carbon-carbon bonds around the ring and six carbon-hydrogen bonds give twelve sigma bonds. The ring also carries three carbon-carbon double bonds in the Kekule structure, and since every double bond is one sigma plus one pi, the extra component is three pi bonds. Option B is wrong because three counts only the pi bonds twice over and ignores the twelve sigma framework. Option C is wrong because six counts only the carbon-carbon sigma bonds and leaves out the six carbon-hydrogen bonds. Option D is wrong because nine is simply a distractor with no basis in the structure. The general rule to carry into the exam is that a single bond is one sigma, a double bond one sigma and one pi, and a triple bond one sigma and two pi.
Read the full article: Chemical Bonding and Reactions: Types, Rules and Facts
Practice Questions
View allWhich of the following is NOT a double displacement reaction?
- A.BaCl2 + H2SO4 → BaSO4 + 2HCl
- B.2H2 + O2 → 2H2O
- C.CuSO4 + H2S → CuS + H2SO4
- D.NaOH + HCl → NaCl + H2O
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In a double displacement reaction two compounds exchange their ions, so both reactants must be compounds. Here hydrogen and oxygen are elements combining to form a single product, water, which makes it a combination reaction and also a combustion and redox reaction, but certainly not a double displacement.
Read the full explanation →Which among the following compounds has a double bond?
- A.Ethane
- B.Methane
- C.Acetylene
- D.Ethylene
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Ethylene, also called ethene, has the formula C2H4, and its two carbon atoms share two pairs of electrons, which is a carbon-carbon double bond made of one sigma and one pi bond; it is the simplest alkene.
Read the full explanation →Which of the following is an amphoteric oxide?
- A.Aluminium oxide
- B.Iron (II) oxide
- C.Magnesium oxide
- D.Carbon dioxide
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An amphoteric oxide reacts with both acids and bases to give a salt and water. Aluminium oxide dissolves in hydrochloric acid to give aluminium chloride and in sodium hydroxide to give sodium aluminate, so it behaves as a base in one case and as an acid in the other.
Read the full explanation →Which of the following is used as a catalyst in the hydrogenation of vegetable oil?
- A.Pb
- B.Ni
- C.H2
- D.He
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Vegetable oils contain unsaturated fatty acids with carbon-carbon double bonds, and when hydrogen is passed through the oil at about 60 degrees Celsius in the presence of finely divided nickel, the double bonds add hydrogen and become saturated, turning the liquid oil into semi-solid vanaspati.
Read the full explanation →A chemical bond formed by the complete transfer of electrons from one atom to another is called a:
- A.Covalent bond
- B.Ionic bond
- C.Coordinate bond
- D.Hydrogen bond
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In an ionic or electrovalent bond a metal atom loses one or more electrons to a non-metal atom; the metal becomes a positive ion and the non-metal a negative ion, and the electrostatic attraction between the two holds the compound together, as in sodium chloride and magnesium oxide.
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