Bonds as a Continuum

CHEMISTRY 11

MS. MCGRATH

Bond Types We have discussed each bond type (covalent and ionic bonds) as a separate and unique entity for the other types of bonds

In reality, bonds exist on a spectrum This spectrum has completely ionic at one end and completely covalent at the other end

We will investigate this spectrum using electronegativities

Electronegativity of Elements

On most periodic tables, electronegativity for almost all elements are stated

Electronegativity refers to the electron affinity of each atom or how strongly held the valance electrons are to the nucleus

Find the atoms with the largest and smallest electronegativities and which have a zero value

Electronegativities Fluorine has the largest electronegativity with a 3.98

◦ This means that fluorine does not easily give up electrons but that it will take electrons from other elements

Francium has the lowest electronegativity with a 0.7◦ This means that francium will give away its electron

but will not attract electrons from other atoms

Electronegativities The Noble Gases do not have an electronegativity This is because the Noble Gases do not want to gain or lose electrons due to their stability

Bond Type and Electronegativity

When considering a bond between two atoms, instead of following previous rules for ionic or covalent, we will now consider difference of electronegativity

To determine the bond type, subtract the smaller electronegativity from the larger

Bond type We will use the following values to determine bond type:

◦ Ionic: > 1.7◦ Polar Covalent: 0.4 - 1.7◦ Slightly Polar Covalent: < 0.4◦ Non Polar Covalent: 0

Water If we consider water, we can see the

ΔEN = ΔENO - ΔENH ΔEN = 3.44 – 2.20 ΔEN = 1.24 which means that it is polar covalent. This means that a water molecule will have a slightly positive end (the hydrogen atoms) and a slightly negative end (the oxygen atom)

Practice Problems

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