Transcript Chemical Bond

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?
OCTET
The eight outer
electrons in an
atom
FACT:
Atoms with full outer
energy levels are very
stable (less reactive)
OCTET RULE
If an atom has 8
electrons in its outer
energy level, it is
unreactive (save He)
Pretend we had a subenergy 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 STRENGTH
the 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 BOND
bond formed between
two ions by the
transfer of electrons
(difference in EN > 1.67)
IONIC COMPOUND
substance formed
when electrons are
transferred between 2
or more substances
(making ions)
COVALENT BOND
bond formed by the
sharing of electrons
(difference in EN < 1.67)
MOLECULE
a 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 BOND
bond formed between
two ions by the
transfer of electrons
IONIC COMPOUND
substance formed
when electrons are
transferred between 2
or more substances
(making ions)