bond polarity(non-polar)

圖片參考：http://imgcld.yimg.com/8/n/HA04717316/o/701101010021413873434880.jpg

The "arrow" sign means the direction of dipole moment.
F is more electronegative than B and thus exert a force to withdraw electrons




圖片參考：http://imgcld.yimg.com/8/n/HA04717316/o/701101010021413873434891.jpg


圖片參考：http://imgcld.yimg.com/8/n/HA04717316/o/701101010021413873434892.jpg

F1 = F2sin30o + F3sin30oF1 = F2(1/2) + F3(1/2) F2cos30o = F3cos30o

∵ F1 = F2 = F3∴ ↑F = ↓F , ←F = →F

2011-01-01 14:09:17 補充：
non-polar: (1) electronegativity difference between atoms is zero or
(2) the vector sum of dipole moment in the molecule is zero

e.g. CH4

2011-01-01 14:11:56 補充：
But, I prefer you to remember the second feature because the first statement is incorrect.
For example, ozone(O3) electronegativity difference between atoms is zero, however, the vector sum of dipole moment in the ozone molecule is not zero and thus O3 is a polar molecule

"non-polar" can be applied to two aspects: bondings and whole molecule.
the difference in electronegativity of oxygen in ozone is indeed zero.
why it's polar is about the mode of bonding -- dative bond is involved.

這也頗為抽象
因為要學到amaths/maths(M2)入面既vector先會明白
dipole moment點樣cancel out