How do you arrange #NH_4^+, BF_3, H_2O, C_2H_2#, in increasing order of bond angle?

1 Answer
Jun 5, 2017

Answer:

Determine Geometry of each.
#NH_4^+ => theta_b = 109^o#
#BF_3 => theta_b = 120^o#
#H_2O => theta_b = 105^o#
#C_2H_2 => H - C-= C - H => theta_b = 180^o#

#H_2O < NH_4^+ < BF_3 < C_2H_2# about both carbon centers.

Explanation:

Geometry of HOH => #AX_2E_2# => Bent angular from an #AX_4# Tetrahedral Parent. The 2 free pair repel the 2 bonded pair to compress the bond angle from #109^o# in a tetrahedron to #105^o# => Bent Angular Geometry.

Geometry of #NH_4^+# is #AX_4# tetrahedral => #theta_b = 109^o#

Geometry of #BF_3# is #AX_3# Trigonal Planar #AX_3# => #theta_b = 120^o#

Geometry of #C_2H_2# is linear through two carbon centers.
=> #H - C-= C - H => theta_b = 180^o#