size of bond angles?

[ChemSiddiqui]

hi i was just wondering how is it so that without any mentioned calculations did my chemistry book have the structure of methane with labelled bond angle? can any 1 tell me how to calculate bond angles? is there any formula to calculate it. help me please.

thnx

[jarmenkill]

methane has 4 electrons groups so it has a 109 28' angel between CH bonds.

for 3 groups of electrons we will have 120 degree(s) angel.(and so 3 bonds are in a plate) for example see BF3

for more info see VSEPR theory