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The highlights are:
1. Covalent Bonding
2. Molecular Compounds
3. Formation of a Covalent bond
4. Characteristics of a Covalent Bond
5. The Octet Rule
6. Multiple Covalent Bond
2.
Covalent Bonding
• A molecule is a neutral group of atoms held
together by covalent bonds.
• A chemical compound whose simplest units are
molecules is called a molecular compound.
compound
Water is a molecular compound.
molecule
3.
Molecular Compounds
• The models for water,
oxygen, and sucrose,
represent a few
examples of the many
molecular compounds
in and around us. Atoms
within molecules may
form one or more
covalent bonds.
4.
•A chemical formula indicates the relative
numbers of atoms of each kind in a
chemical compound by using atomic
symbols and numerical subscripts.
Water:
2 hydrogen atoms
1 oxygen atom
Sucrose:
12 carbon atoms
22 hydrogen atoms
11 oxygen atoms
5.
•A molecular formula shows the types and
numbers of atoms combined in a single
molecule of a molecular compound.
Both chemical formula and
molecular formula.
6.
•A diatomic molecule is a molecule
containing only two atoms.
7.
Formation of a Covalent Bond
• As atoms near each
other the charged
particles begin to
interact.
• The nuclei and electrons
are attracted to one
another, but at the
same time the two
nuclei repel each other
and the electrons repel
each other.
• The attraction forces are
stronger than the
repulsion forces.
8.
Formation of a Covalent Bond
forces are
9.
•As independent particles, most atoms are at relatively
high potential energy.
•Nature, however, favors arrangements in which
potential energy is minimized.
•This means that most atoms are less stable existing
by themselves than when they are combined.
•By bonding with each other, atoms decrease in
potential energy, thereby creating more stable
arrangements of matter.
10.
Potential energy changes during the formation of a
hydrogen-hydrogen bond.
(a)The separated hydrogen atoms do not affect each
(b)Potential energy decreases as the atoms are drawn
together by attractive forces.
(c)Potential energy is at a minimum when attractive
forces are balanced by repulsive forces.
(d) Potential
energy increases
when repulsion
between like
11.
Characteristics of the Covalent Bond
•The distance between two bonded atoms
at their minimum potential energy, that is,
the average distance between two bonded
atoms, is the bond length.
12.
•Bond energy is the energy required to
break a chemical bond and form neutral
isolated atoms.
•All atoms release energy as they change
from isolated individual atoms to parts of
a molecule.
•The same amount of energy must be
added to separate the bonded atoms.
13.
The Octet Rule
•The noble gases are stable because their
atoms’ outer s and p orbitals are
completely filled by 8 electrons.
•Other main group elements can fill their
outermost s and p orbitals with electrons
by sharing electrons through covalent
14.
•Octet Rule – chemical compounds tend
to form so that each atom, by gaining,
losing, or sharing electrons, has an octet
of electrons in its highest occupied
energy level.
15.
Exceptions to the Octet Rule
• Hydrogen forms bonds in which it is
surrounded by only two electrons.
• Boron has just three valence electrons, so it
tends to form bonds in which it is surrounded
by six electrons.
• Main group elements in Periods 3 and up can
form bonds with expanded valence, involving
more than eight electrons.
16.
Electron-Dot Notation
•Electron-dot notation is an electron-
configuration notation in which only the
valence electrons of an atom or a
particular element are shown, indicated
by dots placed around the element’s
Hydrogen has 1 valence
electron so one dot is placed
around the symbol.
17.
How many valence
electrons does carbon
Notice one dot is placed on
each side of the symbol.
How many valence electrons
does fluorine have?
Notice one dot is placed on
each side of the symbol
before placing a second.
18.
Electron-Dot Notation for Groups 1, 2,
13-18
19.
Lewis Structures
•Electron-dot notation can also be used
to represent molecules.
•A hydrogen molecule, H2, is represented
by combining the notations of two
individual hydrogen atoms. Remember that
hydrogen is
“happy” with two
electrons instead
of eight.
Remember each
hydrogen has one Shared electron pair
valence electron that (called a bonding pair).
it brings to the bond.
20.
Will two fluorine atoms form a bond?
Each fluorine atom has 7 valence electrons so each
fluorine atom wants to gain one electron to achieve
an octet.
Neither atom will give up an electron – remember fluorine
highly electronegative.
What’s the solution - what can
they do to achieve an octet?
21.
The octet is achieved by each atom sharing the
electron pair in the middle.
A lone pair is a pair
of
electrons that is not
involved in bonding
and that belong
exclusively to one
atom.
octet octet
This is the shared pair
called the
bonding pair.
It is a single bonding pair and is called
a single bond.
22.
Often the shared pair of electrons in a
covalent bond is replaced by a long dash.
Shared pair Replace with long dash.
23.
•These representations are all Lewis
Structures, formulas in which atomic
symbols represent nuclei and inner-shell
electrons, dot-pairs or dashes between
two atomic symbols represent electron
pairs in covalent bonds, and dots
adjacent to only one atomic symbol
represent unshared electrons.
Unshared electrons.
Atomic symbol –
represents nuclei
Electron pair and inner-shell
in electrons.
24.
•A structural formula indicates the kind,
number, arrangement, and bonds but not
the unshared pairs of the atoms in a
Structural formula
25.
Multiple Covalent Bonds
•A double bond is a covalent bond
produced by the sharing of two pairs of
electrons between two atoms.
•A triple bond is a covalent bond produced
by the sharing of three pairs of electrons
between two atoms.
26.
O O
How will two oxygen atoms bond?
Each atom has two unpaired electrons.
Each atom wants to gain two electrons to
achieve an octet.
27.
7 electrons
O O 7 electrons
If we share one pair of electrons will
each oxygen atom have an octet?
28.
O O
6 valence electrons 6 valence electrons
plus 2 shared plus 2 shared
electrons = full octet electrons = full octet
What if we share two pairs of electrons?
Both electron pairs are shared.
29.
O O
two bonding pairs
making a double
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