VII Atomic Structure C

Bonding

Bonding

• Bonding between atoms in a compound comes from the sharing of electrons

• The kind of bond formed between the two atoms depends on the amount of sharing of the electrons

Bonding in Compounds

• Kinds of Bonds

Ionic

electron transferred from one atom to another

generally between a metal cation and a non metal anion

Covalent

electrons shared between 2 atoms in a bond

• Electronegativity– Measure of the ability of an atom in a bond

to attract the bonding electrons– Across a Period: EN increases– Down a Group: EN decreases– Most electronegative element is fluorine

Li Be B C N O F1.0 1.5 2.0 2.5 3.0 3.5 4.0Na Mg Al Si P S Cl0.9 1.2 1.5 1.8 2.1 2.5 3.0K Ca Ga Ge As Se Br0.8 1.0 1.6 1.8 2.0 2.4 2.8

Determine the amount of covalent or ionic character in a bond

Using Electronegativity

• The difference in electronegativity between two atoms can be used to determine how ionic or how covalent the bond is

Difference in electronegativityEN

EN = 1.7 = 50% ionic

EN > 1.7 more ionic

EN < 1.7 more covalent

The larger the EN, the more ionic the bond

The smaller the EN, the more covalent the bond

So the farther apart the atoms are the more ionic the bond

Compare three bonds:

A) C--F B) O--F C) N--F

Which is the most ionic?

Compare three bonds:

A) C--F B) O--F C) N--F

Which is the most covalent?

1. The bond with the smaller cation is the more covalent bond

2. The bond with the larger anion is the more covalent bond

3. The bond with the larger charge on the cation or anion is the more covalent bond

4. The bond with a transition metal cation is the more covalent bond

•Determine the amount of covalent or ionic character in a bond

•Fajan’s Rules of Covalency

• Predict which is the more covalent

A) SbCl3B) BiCl3

C) BeOD) BeS

E) Tl2O

F) Tl2O3

G) NaClH) CuCl

Sb is smaller than Bi, so the SbCl3 ismore covalent

S is larger than O, so the BeS is more covalent

Compare Tl+ and Tl+3 , thallium(III) oxidemore covalent

Cu is a transition metal, CuCl more covalent

Which is the Most Covalent?

A) MgCl2B) MgBr2

C) CaCl2D) CaBr2

Which is the Most Covalent?

A) MgCl2B) MgBr2

C) CaCl2D) CaBr2

Compare: Mg cation and Ca cation.Mg smaller than Ca so Mg compounds more covalent

Compare: Cl anion and Br anion.Br larger than Cl, so Br compounds more covalent

Which is the Most Ionic?

A) MgCl2B) MgBr2

C) CaCl2D) CaBr2

Which is the Most Ionic?

A) MgCl2B) MgBr2

C) CaCl2D) CaBr2

Most ionic is the same as least covalent

Compare: Mg cation and Ca cation.Mg smaller than Ca so Mg compounds more covalent, Ca more ionic

Compare: Cl anion and Br anion.Br larger than Cl, so Br compounds more covalent, Cl more ionic

Which of the following is least covalent?

A) Cu2O

B) CuO

C) Cu2S

D) CuS

Which of the following is least covalent?

A) Cu2O

B) CuO

C) Cu2S

D) CuSCompare anions O and S. S is the larger anion, so it forms more covalent bonds. Therefore, Cu2O and CuO are less covalent

Cu2O is Cu+1, CuO is Cu+2 , the larger charge is more covalent, so Cu2O is the least covalent

Which of the following is least ionic?

A) AgCl

B) NaCl

C) AuCl

D) RbCl

Which of the following is least ionic?

A) AgCl

B) NaCl

C) AuCl

D) RbCl

Least ionic is Most covalent

Ag and Au are transition metals, so they are more covalent than Na and Rb which are Group 1 Alkali metals.

Compare Ag and Au. Ag is the smaller size so it forms the most covalent bond.

• Bond polarity– Because electrons are shared unequally in

a bond due to the difference in electronegativity, a covalent bond has a positive end and a negative end. (poles)

– The bond is said to be polar

H ---Cl– Bond dipole - occurs when you have a

polar bond– Dipole moment () - is a measure of the

bond dipole (the amount of polarity)

+ -

• Bond Polarity– The more ionic the bond the more polar the

bond– The more ionic the bond, the larger the bond

dipole– The more ionic the bond, the greater the dipole

moment.

Compare three bonds:

A) C--F B) O--F C) N--F

Which is the least polar bond?