Polar Covalent Bonds Electron pairs in covalent bonds are not always shared equally This affects the...

Polar Covalent BondsElectron pairs in covalent bonds are not

always shared equallyThis affects the properties of the compoundRemember electronegativity?

The atom with the higher electronegativity attracts the bonding electrons more.

Electrons are pulled closer to this atom.

Example: HClDraw the Lewis Structure for HCl

The bonding pair are pulled more towards the most electronegative atom...which one is that?

Review: Naming Binary AcidsThese are covalent compoundsThey do not contain oxygenThey are named using ionic naming

conventionsEg. HCl hydrogen chloride

HBr hydrogen bromide HCN hydrogen cyanide (not binary)The form ions in water (this is why they are

named like ionic compoundsTo name when in water (aqueous)

Drop hydrogen, add “hydro” to root, change ending to “ic acid”

Hydrogen chloride hydrochloric acid

IUPAC names for binary acidsThe general form “aqueous hydrogen _______”

is usedEg. HCl aqueous hydrogen chloride

HBr aqueous hydrogen bromide

Space Filling Model of HClIf we look at a model of HClWe find that the bonding pair is

pulled more toward ClCl becomes slightly – ( we use the symbol δ-)H becomes slightly + ( we use the symbol δ+)This small difference in charge within a

covalent molecule is called a dipole

Polar Covalent BondsIf a molecule has a dipole we refer to the

bond as a polar covalent bondThe molecule itself is considered to be polarThe difference in electronegativity b/n the

atoms involved determines how polar the bond will be.

Electronegativity differenceFor F-H bonds

The electronegativity of H is 2.1The electronegativity of F is 4.0The electronegativity difference = 4.0-2.1 =

1.9This bond is very polar!For C-H bondsThe electronegativity difference = 2.5-2.1 =

0.4This is only slightly polar

Determining the polarity of a bond

If the electronegativity difference is less than 0.5, the bond is considered slightly polar

Covalent bonds are completely non-polar only when the 2 atoms are identical Eg. H2

The electronegativity difference is also called the ionic character of the bond

Is a bond polar covalent or ionic?If the ionic character is > 1.7, the bond is

considered to be ionicIt is hard to tell the difference between highly

polar covalent bonds and ionic bondsTherefore, we usually consider, metal + non-

metal bonds to be ionic and non-metal + non-metal bonds to be covalent

Bonding Continuum

Predicting Polarity1. For the following pairs of atoms, use

electronegativity to determine if the bond will be non-polar, polar covalent or ionic

a) calcium and chlorineb) nitrogen and brominec) carbon and fluorine

2. For the above pairs, indicate which atom will be slightly positive and which one will be slightly negative.

3. Determine the bond polarity in the compound IF. Is it slightly polar or very polar?