▁of ▁bond ed ▁electrons ▁and ▁two ▁un shared ▁l one ▁pairs . ▁ ▁T etra hed ral : ▁T etra - ▁sign ifies ▁four , ▁and ▁- hed ral ▁rel ates ▁to ▁a ▁face ▁of ▁a ▁solid , ▁so ▁" t etra hed ral " ▁literally ▁means ▁" h aving ▁four ▁faces ". ▁ ▁This ▁shape ▁is ▁found ▁when ▁there ▁are ▁four ▁b onds ▁all ▁on ▁one ▁central ▁atom , ▁with ▁no ▁extra ▁un shared ▁electron ▁pairs . ▁ ▁In ▁accord ance ▁with ▁the ▁V SE PR ▁( val ence - shell ▁electron ▁pair ▁rep ulsion ▁theory ), ▁the ▁bond ▁angles ▁between ▁the ▁electron ▁b onds ▁are ▁ar cc os ( − ) ▁= ▁ 1 0 9 . 4 7 ° . ▁For ▁example , ▁m eth ane ▁( CH 4 ) ▁is ▁a ▁t etra hed ral ▁mole c ule . ▁▁ ▁Oct ah ed ral : ▁Oct a - ▁sign ifies ▁eight , ▁and ▁- hed ral ▁rel ates ▁to ▁a ▁face ▁of ▁a ▁solid , ▁so ▁" oct ah ed ral " ▁means ▁" h aving ▁eight ▁faces ". ▁The ▁bond ▁angle ▁is ▁ 9 0 ▁degrees . ▁For ▁example , ▁sul fur ▁hex a flu or ide ▁( SF 6 ) ▁is ▁an ▁oct ah ed ral ▁mole c ule . ▁ ▁Tr ig onal ▁py ram idal : ▁A ▁trig onal ▁py ram idal ▁mole c ule ▁has ▁a ▁py ram id - like ▁shape ▁with ▁a ▁tri angular ▁base . ▁ ▁Un like ▁the ▁linear ▁and