Transcript 6.2 Power Point Notes

Chapter 6.2 Notes
Sharing Electrons
1.Sharing Electrons
a. A covalent bond is a chemical bond in
which two atoms share a pair of
valence electrons.
i. When two atoms share one pair of
electrons, the bond is called a single
bond.
Sharing Electrons
ii.
Atoms can share more than one
valence electron. When they
share two it is called a double
bond, when they share three it
is called a triple bond.
Models of Covalent Bonds
a. Four ways to represent models of covalent
bonds are the electron dot diagram, the
structural formula, the space-filling model,
and the electron cloud model.
i. In the electron dot model, the bond is
shown by a pair of dots in the space
between the symbols.
Models of Covalent Bonds
ii.
iii.
In the structural formula, the pair
of dots is replaced by a line.
The electron cloud and the spacefilling models show the orbitals of
atoms overlap when a covalent
bond forms.
Molecular Models
Molecules of Elements
2. Molecules of Elements
a. A molecule is a neutral group of atoms
that are joined together by one or more
covalent bonds.
i. In the formula H2O, the subscript 2
indicates that there are two hydrogen
atoms.
Molecules of Elements
ii.
iii.
1.
The H2, hydrogen, molecule is neutral
because it contains two protons and two
electrons, one from each hydrogen atom in the
molecule.
In the H2 molecule, what keeps the hydrogen
atoms together?
The attractions between the shared electrons and
the protons in each nucleus hold the atoms
together in a covalent bond.
Molecules of Elements
b. A chemical formula can be used to
describe the molecules of an element
as well as a compound.
c. When atoms join in pairs we call them
diatomic molecules.
Unequal Sharing of Electrons
3. Unequal Sharing of Electrons
a. Atoms are able to share electrons
unequally.
i. Elements on the right side of the
periodic table have a greater
attraction for electrons than elements
on the left side.
Unequal Sharing of Electrons
ii.
Elements at the top have a greater
attraction for electrons than do
elements at the bottom.
1.
For example, fluorine is at the top
right of the periodic table and has the
strongest attraction for electrons in
the non-metal group.
Unequal Sharing of Electrons
iii.
Ionization energy is the amount
of energy needed to remove an
electron from an atom.
1.
Ionization energy increases as
you move up and to the right on
the periodic table.
Ionization Energy
Polar Covalent Bonds
4. Polar Covalent Bonds
a. A polar covalent bond is a bond in which
electrons are not shared equally.
i. When atoms form a polar covalent bond,
the atom with the greater attraction for
electrons has a partial negative charge
represented as - ( is the lower case
symbol of the Greek symbol delta).
Polar Covalent Bonds
ii.
The other atom has a partial
positive charge represented as +.
1.
When hydrogen and chlorine bond,
the shared electron is closer to the
chlorine atom, because chlorine has a
greater attraction for electrons. This
gives the chlorine atom a slightly
negative charge and the sodium atom
a slightly positive charge.
Polar Covalent Bonds (HCl)
Polar Covalent Bonds
iii.
Attractions between polar
molecules are stronger than
attractions between nonpolar
molecules.
Polar VS Non-Polar Molecules
5. Polar VS Non-Polar Molecules
a. When a molecule contains only two atoms, such
as H2, the molecule will always be polar.
b. Molecules that contain more than one polar bond
are not always polar molecules.
i. The type of atoms in a molecule and its shape
are factors that determine whether a molecule is
polar or nonpolar.
Polar VS Non-Polar Molecules
1. For
example, in the CO2 molecule,
there are double bonds between each
oxygen atom and the central carbon
atom. Since oxygen has a greater
attraction for electrons than carbon,
each double bond is polar. However,
there is an equal pull on the electrons
from opposite directions which cancel
out and make the molecule nonpolar.
CO Molecule
2
Polar VS Non-Polar Molecules
2.
In a H2O molecule, the bonds are polar
because oxygen has a greater attraction for
electrons than hydrogen does. However,
since there is not an equal pull on the
electrons, the hydrogen atoms are both
located on the same side of the oxygen
atom and create a polar molecule. The
hydrogen side of the molecule has a partial
positive charge, and the oxygen side has a
partial negative charge.
H O Molecule
2
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