Bond.Chemical Bond.

ELECTRONEGATIVITY

The tendency of an atom to attract electrons to

itself when it is bonded to another atom

Check out Figure 5-20

on page 151•Where are electronegativities the greatest?

•The least?

The eight outer electrons in an

atom

OCTET

FACT:Atoms with full outer energy levels are very stable (less reactive)

If an atom has 8 electrons in its outer

energy level, it is unreactive (save He)

OCTET RULE

Pretend we had a sub-energy level with 12

electrons. When would it be most

stable?(The egg carton example)

FACT #2:Atoms with filled,

half filled, or empty sub-energy levels are slightly more stable

Now…how do we make ENERGY LEVELS more

stable?

Ways to make full outer energy levels:

•Add electrons to a partially filled outer energy level•Lose all electrons in the outer energy level•Share electrons with another atom

Periodic Trends

ATOMIC RADIUS

The distance from the center of the nucleus

to the outermost energy level

The atomic radius INCREASES

within a group

(just adding energy levels)

The atomic radius DECREASES

within a period

(more positive charge pulling e-)

SHIELDING EFFECT

The positive pull is less because the distance between nucleus and electrons is greater

IONIZATION ENERGY

the energy required to remove an electron

from an atom

The ionization energy

INCREASES across a period

(more p+ have more pull on e-)

The ionization energy DECREASES as you

go down a group

(shielding effect)

ELECTRON AFFINITY

how much an atom desires another

electron

The electron affinity DECREASES as you

go down a group

(shielding effect)

The electron affinity INCREASES across a period

(except for the noble gases)

(more p+ have more pull on e-)

BOND STRENGTHthe energy needed to

break the bonds between atoms in a

compound

Bond Strength

The greater the difference in electronegativities, the greater the bond strength

BONDING OPTIONS• By transferring electrons

(producing ions)(big difference in EN)

• By sharing electrons(small difference in EN)

IONIC BONDbond formed between

two ions by the transfer of electrons

(difference in EN > 1.67)

IONIC COMPOUNDsubstance formed when electrons are

transferred between 2 or more substances

(making ions)

COVALENT BONDbond formed by the sharing of electrons

(difference in EN < 1.67)

MOLECULEa neutral group of

atoms held together by covalent bonds

(ex: H2O)

WHICH IS STRONGER?

Ionic bonds are stronger than

covalent

Bonds in all the polyatomic ions and

diatomics are all covalent bonds

IONIC BONDbond formed between

two ions by the transfer of electrons

IONIC COMPOUNDsubstance formed when electrons are

transferred between 2 or more substances

(making ions)