PHYSICAL SCI: LEWIS DOT STRUCTURES & SHAPES OF MOLECULES

Lewis Dot symbols

• Formation of compounds or molecules can be understood by using the knowledge on electron configuration, periodic table and Lewis dot structure.

• Proponent: Gilbert Newton Lewis

Valence Electrons

• The electrons found in the outermost valence shell or an orbital

• The ones that participate in chemical reactions

• Number of valence electrons an atom has corresponds to the atom’s group (vertical column) in the periodic table

• Unpaired valence electrons represent electrons available for bonding or for linking with other elements

Lewis Dot structures

• Diagrams that show how atoms in a molecule are bonded together

• The atom with the most unpaired electrons will be in the middle

VSEPR THEORY (Valence Shell Electron Pair Repulsion)

• States that pairs of valence electrons on the central atom will be arranged in space to put the greatest distance between the electrons

• There is a repulsion between the pairs of valence electrons in all atoms

• Each atom in a molecule will achieve a geometry that minimizes the repulsion between electrons in the valence shell of that atom

VSPER Notation

AXE

A

the central atom

X

atoms bonded to the central atom

E

lone pairs of electrons

Electron Pair Repulsion

• The principle that electron pairs around a central atom tend to orient themselves as far apart as possible

Linear

• 180 angle

• 2 bonds

Trigonal Planar

• 120 angle

• 3 bonds

Trigonal Pyramidal

• < 109.5 angle

• 3 bonds

Bent #1

• < 120 angle

• 2 bonds

• 2 lone pairs

Bent #2

• > 120 angle

• 2 bonds

• 1 lone pair

Trigonal Bipyramidal

• < 120 angle

• 5 bonds

Octahedral

• 90 angle

• 6 bonds