Predicting Shapes of Molecules

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Presentation transcript:

Predicting Shapes of Molecules VSEPR Valence Shell Electron Pair Repulsion Theory

Why not the shape of ionics?

Linear (straight line) Any 2 atom molecule is linear O2 H2 HCl . . . etc.

Steps to predicting shapes Draw the dot structure Count the electron domains surrounding the central atom Single bonds count as one Double and triple bonds count as one lone electron pairs (unbonded) count as one

Determine the category (electron geometry) based on regions of electron domains 2 domains - Linear 3 domains – trigonal planar 4 domains - tetrahedral 5 domains – trigonal bipyramidal 6 domains - octahedral http://safeshare.tv/w/BUalxrqbEK

FINALLY Name the shape of the molecule (molecular geometry) based on the arrangement of the ATOMS Lone pairs are repulsive and force the bonded electrons together and reduce the bond angles AND change the shape

Practice… Shape & bond angles? H2Se Bent w/ ~1050 angles CH2Cl2 Tetrahedral w/ 109.5o angles PCl3 Trigonal pyramidal w/ 107o angles

Types of Covalent MOLECULES POLAR vs. NON-POLAR

non-polar Have symmetrical electron distributions. IF THERE ARE POLAR bonds, they all cancel each other out.

Polar molecules (a.k.a. Dipoles) Occurs because of a polar bond between 2 atoms O C δ- δ+

Or uneven charge (e-) distribution in the molecule Cl H δ- δ+

Another example of asymmetrical distribution of electrons Trigonal pyramidal Bent polarity

Water is asymmetrical δ- O H H δ+

Water is a bent molecule H H

W - A - T - E - R as bent as it can be! Water’s polar MOLECULE! The H is positive The O is not - not - not - not

W - A - T - E - R as bent as it can be! Water’s polar MOLECULE! The H‘s are the ears The O’s the nose - nose - nose - nose

W - A - T - E - R as bent as it can be!

Making sense of the polar non-polar thing COVALENT BONDS or MOLECULES non-polar are between identical atoms or very small e-neg difference up to ~0.4 All other bonds with e-neg difference up to ~2.0 are polar Non-polar Even distribution of electrons Polar bonds cancel out cancel Polar asymmetrical UNEVEN electron distribution

The End