Answer:
[tex]\boxed{\text{$\sigma$(sp-sp$^{3}$); 180$^{\circ}$}}[/tex]
Explanation:
(a) Hybridization of orbitals
See the Lewis structure of propyne in the first diagram below.
C1 is directly bonded to two other atoms (H and C2) so it is sp hybridized.
C2 is directly bonded to two other atoms (C1 and C3) so it is sp hybridized.
C3 is directly bonded to four other atoms (C2 and 3 H) so it is sp³ hybridized.
(b) C2-C3 Sigma Bond
See the atomic and molecular orbitals in the second picture below.
C3 is using its hybrid atomic orbitals to form sigma molecular bonds. The C2-C3 sigma bond is formed by the overlap of the C2 sp atomic orbital with the C3 sp³ atomic orbital to make a σ(sp-sp³) molecular orbital.
(c) Bond angles
C1 and C2 are sp hybridized. Since the angle between sp orbitals is 180°, all atoms directly attached the C1 and C2 must be in a straight line. The C-C-C bond angle is 180°.
