Electronegativity & Polarity Flashcards
Review: Electronegativity
Invented by Linus Pauling, electronegativity is the ability of an individual atom, when bonded, to attract bonding electrons to itself
It is a scale, not a measurement!
How to identify if a bond is polar or covalent
Ionic bonds are between a metal and a non-metal, and molecular (covalent) bonds are between non-metals, right?
Yes, but there’s a more formal distinction!
To truly predict whether a bond is ionic or covalent, we must calculate the difference in the elements’ electronegativities!
ΔEN
Electronegativty Difference: Multiple atoms
Don’t multiply or change the number of electronegativity if there are multiple atoms. Keep the number the same.
ΔEN indicates the degree to which a chemical bond is ionic or covalent!
(What are the scale numbers?)
0-0.4 : Non-polar Covalent
Equal Sharing of electrons
0.41-1.69 : Polar Covalent
Unequal sharing of electrons (one element pulls more)
>1.7 Ionic
No sharing of electrons in bond.
Non-Polar Covalent Bonds (0 <ΔEN ≤ 0.4)
When the atoms are identical (ΔEN = 0), they share the electrons equally!
This is called a non-polar covalent bond
Example: H2
Polar Covalent Bonds (0.4 <ΔEN < 1.7)
When two covalently bonded atoms have significant electronegativity differences (0.4 <ΔEN < 1.7), they do NOT share electrons equally
Consider the bond between hydrogen and chlorine:
ΔEN = 3.2 – 2.2
= 1.0
H and Cl have a polar covalent bond!
One element is pulling electrons more. The greater the number, the greater the pull. Chlorine has the greater pull.
Ionic Bonds (ΔEN ≥ 1.7)
A bond between two atoms with ΔEN greater than or equal to 1.7 is an ionic bond
ΔEN = 3.2 – 0.9
= 2.3
A complete transfer of electrons.
Drawing Conventions for Polar Covalent Bonds
(Diapole Movements in Diagram)
Use arrows to show bond dipoles/dipole moments
They point towards the more electronegative atom in the bond
Partial charges (δ+ and δ-) are also used to show the relative charges in a polar covalent bond
only for polar covalent bonds** only use arrows for unequal pulls, is it is a non-polar covalent bond, they shared electrons equally. Do not draw arrow for this.
Polar Molecules
A polar molecule is slightly positively charged at one end and slightly negatively charged at the other because of electronegativity differences
Consider HCl
The molecule has a positively charged end and a negatively charged end, so the whole molecule is therefore polar
**does not include the middle. Ex.Co2 is not a polar molecule
Bent Polar Molecules; Water
Since the water molecule is lopsided, or bent, we can consider that it has two ends: a negatively charged oxygen end and a positively charged hydrogen end.
*this is due to the shape that it is a polar, molecule. draw shapes correctly to make sure. water is a bent molecule.
Non-Polar Molecules (Charges)
All molecular elements are non-polar
No dipole moments and partial charges are drawn!
If a molecule has polar BONDS, is the molecule ALWAYS polar?
Not all molecules containing polar covalent bonds are polar molecules!
Consider carbon tetrachloride (CCl4)
Since a molecule of CCl4 is symmetrical, it lacks oppositely charged ends and so is NOT polar.
*non-polar because the ends are all the same charge.
Bent shape
2 bonding pairs (central atom)
2 lone pairs (central atom)
Polar molecule (if polar covalent bonds)
Bonding Pairs
Bonding pairs – the # of bonds to the atom (count double/triple bonds as ONE bond)
Trigonal Pyramidial Shape
3 bonding pairs
1 lone pair
Polar molecule
(if polar covalent bonds)
The bottom of the molecule is positive. The top is negative.
