Hybridization and sigma/pi bonds (HL)
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Flip to reveal answersHow does a σ (sigma) bond form?
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Question
How does a σ (sigma) bond form?
Answer
By **head-on (end-to-end)** overlap of orbitals, with electron density **along the bond axis**. Every single bond is a σ bond.
Question
How does a π (pi) bond form?
Answer
By **sideways** overlap of two parallel **p orbitals**, with electron density **above and below** the bond axis.
Question
How many σ and π bonds in a single, double and triple bond?
Answer
Single = **1 σ**; double = **1 σ + 1 π**; triple = **1 σ + 2 π**. Every multiple bond has exactly **one** σ.
Question
What is hybridization?
Answer
The **mixing** of an atom's atomic orbitals (1 s + some p) into a set of equal-energy **hybrid orbitals**, one per electron domain.
Question
sp³ — domains, shape, π bonds?
Answer
**4** domains (1 s + 3 p), **tetrahedral**, 109.5°, **0** π bonds (all single bonds).
Question
sp² — domains, shape, π bonds?
Answer
**3** domains (1 s + 2 p), **trigonal planar**, 120°, leaves **1** p orbital → **1 π** bond.
Question
sp — domains, shape, π bonds?
Answer
**2** domains (1 s + 1 p), **linear**, 180°, leaves **2** p orbitals → **2 π** bonds.
Question
How do you deduce an atom's hybridization?
Answer
**Count its electron domains** (σ bonds + lone pairs): 4 → sp³, 3 → sp², 2 → sp.
Question
How do you count σ and π bonds in a molecule?
Answer
**σ = total number of bonds** between atoms; **π = (number of doubles) + 2 × (number of triples)**.
Question
Why do π bonds restrict rotation?
Answer
The two p orbitals must stay **parallel** to overlap; twisting breaks the π bond, so a C=C cannot rotate → causes **cis–trans isomerism**.
Question
Hybridization of each C in ethene, CH_{2}=CH_{2}?
Answer
Both are **sp²** (3 domains each), trigonal planar; the C=C is 1 σ + 1 π.
Question
Hybridization of the C≡N carbon in a nitrile?
Answer
**sp** — it has 2 electron domains (the triple bond + one single bond), so it is linear.
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