The Sharing and Transferring of Electrons
http://www.youtube.com/watch?v=QqjcCvzWwww
There is a certain number of electrons that is
optimal for atoms to have in their energy shells.
That number is 8 and is called an octet.
When an atom has eight electrons in an energy
shell, the atom obtains a lower state of energy
and is stable.
Ionic bonds are achieved through the transfer of
valence electrons (outermost energy shell electrons).
Metals that have three or less electrons, in their
valence energy shells, tend to transfer their
electrons to nonmetal elements that possess five, six
or seven electrons in their valence energy shells.
The transfer of valence electrons forms positively
and negatively charged “ions”. These oppositely
charged ions are attracted to each other. The
attractions hold the ions together and formula
units are formed.
However, the number of ionically bonded
compounds is quite small compared with the total
number of compounds formed in the universe.
The vast majority of compounds are formed from
sharing valence electrons.
These bonds are called covalent bonds and the
compound that is formed is called a molecule.
In a molecule, the electrons are considered to be part
of the valence shell of both atoms.
Hydrogen and oxygen are both _____________.
If they bond together, would we expect an ionic
bond or covalent bond to form?
How many hydrogen atoms would be needed to
bond to one oxygen atom?
Let’s consider water, H2O, as an example.
Hydrogen has one electron in its only energy shell.
________ electrons can fit in this inner energy shell.
Oxygen has six electrons in its outermost energy
shell (valence energy shell); it wants __________.
By sharing their valence electrons, both hydrogen
and oxygen acquire an octet completing their
outermost energy shells (valence shells).
Possessing an octet in the valence energy shell
causes atoms to be more __________.
The graphic we saw of H2O shows all of the
electrons that belong to hydrogen and oxygen.
Lewis Dot Diagrams are more convenient to use.
They only show the electrons we are interested in,
the valence electrons.
The shared electrons are shown as dashes and
the remaining electrons (not being shared) are
paired up and called “lone pairs”.
A water molecule has ________shared electrons
(two shared pairs), shown here as dashes, and
_______ lone pairs of electrons.
How many valence electrons does carbon have?
How many valence electrons does carbon need to
complete its octet?
How many valence electrons does hydrogen have?
How many valence electrons does hydrogen need to
complete its valence?
Draw what you think a molecule between
hydrogen and carbon would look like.
(HINT: Start with carbon as the center of the molecule)
Methane has _______ shared pairs of electrons and
________ lone pairs of electrons.
How many electrons does sulfur need to complete its
valence energy shell? If sulfur formed bonds with
hydrogen, how many hydrogen atoms would be
needed?
When sulfur and hydrogen bond, _______electrons are
shared (each dash represents ______shared electrons).
There are _____lone pairs of electrons in H2S molecule.
Electronegativity describes electron affinity.
In other words, it is a measure of the tendency
of an atom to accept an electron.
Bonding is often not clearly ionic or covalent.
One of the periodic table trends we observed
was that electronegativity _____________ as you
move from left to right across the periodic table.
To find the difference in the electronegativity
between two elements, you ___________their
electronegativity values.
If the electronegativity difference between two
bonding elements is very large, the element
with the larger electronegative value will “grab”
the valence electrons . This transfer of
electrons leads to an ionic bond. If the difference
is small the electrons will be shared. This
sharing of electrons leads to a covalent bond.
Ionic (transfer)
∆ EN 3.3
Mostly Ionic
∆ EN > 1.7
Mostly Covalent (Polar)
Unequal sharing of electrons
∆ EN 0.4 – 1.7
Covalent (Non-polar)
Equal sharing of electrons
∆ EN = 0.0
The bonding between hydrogen and chlorine:
Cl EN value
3.16
H  EN value
-2.20
.96
The electronegativity difference is .96 which
means the bond formed between chlorine and
hydrogen is a covalent bond and a HCl molecule
is the result.
The bonding between sodium and chlorine:
Cl  EN value
3.16
Na  EN value
-0.93
2.23
The electronegativity difference is 2.23 which
means the bond formed between chlorine and
sodium is an ionic bond and a NaCl formula unit
is the result.