Polarity

Compound Review

Compound: a chemical combination of two or more elements

Why do elements chemically combine?

They want to achieve full energy levels

Full energy level = stability

Elements will move electrons for them to be satisfied

Electronegativity

• The attractive force that an atom of an element has for shared electrons

• Atoms have different electronegativities– Electrons will spend more time near atom with

stronger (larger) electronegativity

Electronegativity

EOS

Electronegativity

Polar Covalent

• Remember ionic bonds transfer electrons, while covalent bonds share electrons.

• All atoms do not attract their electrons in a bond to the same degree.

• One can determine the degree to which electrons are transferred or shared using the electronegativity difference

Polar Covalent• Remember…electronegativity is a measure

of an atom’s ability to attract the pair of electrons it shares with another atom.

• In general, metals have lower electronegativities than non metals

• Each atom’s electronegativities has been determined by experiences and can be found in your textbook on pg 71.

EN Differences• To find ΔEN, subtract the EN of 2 atoms.

EN must be a real number. (ie. No negatives!)

• If the ΔEN is:• 3.3-1.7 = an ionic bond• 1.6-0.5 = polar covalent• 0.5-0.1 = slightly polar covalent• 0.0 = non-polar covalent

• Determine the classification of these bonds:A) B & P B) S & O C) Li & O D) Mg & N=0.15 slight polar =0.86 polar =2.46 ionic =1.73 ionic

Polar vs Nonpolar CovalentNonpolar Covalent Bonds

• Between two atoms with similar EN

• Electrons are shared equally between the two

• Nuclei from each atom are attracting the electrons with equal force

• There is little or no positive & negative charges present

Polar Covalent Bonds• Between two atoms with

moderate difference in EN• Electrons are not shared

equally• Results in a localized

negative and positive charge• The atom with higher EN

will be slightly negative and other will be slightly positive

• Bigger the difference, the more polar the bond

Dipole Moments

• In polar molecules, we indicate their positive or negative partial charges using δ- and δ+ and their polarity or “dipole moment”

Hδ+ Fδ-

Hδ+ Hδ+

Oδ-

• Dipole Dipole moments occur when there is an instant in time when the electrons are distinctly unequally shared.