the octet rule all atoms “want” a full valence shell of e- this makes them more stable, like the...
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The Octet Rule
All atoms “want” a full valence shell of e-
This makes them more stable, like the Noble Gases, which have 8e-, a full valence shell.
For H and He a full valence shell is 2 e-
For all bigger atoms, a full valence shell is
8 e- (hence “octet”)
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The Octet Rule
All atoms “want” their valence shell to mimic a Noble Gas e- configuration:
Most chemical reactions are the result of atoms gaining or losing or sharing e- with other atoms in order to have 8 valence e-
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Covalent Bonding
Definition: two or more atoms sharing valence e- so that each atom has a full valence shell (2 e- for H and He, 8 e- for all bigger atoms)
H Cl
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Covalent Bonding
Definition: two or more atoms sharing valence e- so that each atom has a full valence shell (2 e- for H and He, 8 e- for all bigger atoms)
ClH
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When does covalent bonding occur?
1) Between elements that are non metals
2) Between two elements with an electronegativity difference of less than
1.7
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How do I find the electronegativity difference between 2 atoms?
Using Table S, look up the electronegativity values for each atom. Then find the difference by subtracting the smaller value from the bigger value:
H = 2.1 Cl = 3.2 Electronagativity difference = 3.2 -2.1 = 1.1Since 1.1 is less than 1.7, this bond is covalent
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Forming a Covalent Bond
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Non- polar covalent bonds
NON POLAR covalent bonds occur when the electronegativity difference of the two bonded atoms is zero.
When does this happen?
When the two bonded atoms are identical
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Non- polar covalent bonds
All Diatomic atoms have non-polar covalent bonds:
H2 N2 O2 F2 Cl2 Br2 I2
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Non- polar covalent bonds
In a non polar covalent bond, the shared electrons are shared equally between both atoms
This means they spend equal amounts of time orbiting both nuclei
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Double covalent bonds
Some atoms can share TWO electrons with another atom. This results in a double bond.
OO
Each oxygen atom has 6 valence e-
By sharing 2 e- pairs, they will each fill their
Valence shell with 8 e-
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Double covalent bonds
OO
Each oxygen atom has 6 valence e-
By sharing 2 e- pairs, they will each fill their
Valence shell with 8 e-
Double bond
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Lewis dots can get tedious to draw for double bonds, so often the “stick” model is used instead:
One represents a shared pair of e-
O O
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Triple covalent bonds
Some atoms, like nitrogen, can form a triple covalent bond with other atoms
Each atom shares 3 of its valence e-
N N
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POLAR covalent bonds
Except for diatomic molecules, most covalent bonds are POLAR
This means one atom is more electronegative than the other, and the e- are NOT SHARED EQUALLY
The e- spend more time near the nucleus of the more electronegative atom
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H Cl
Since Cl is more electronegative than H,
The H-CL bond is polar
Since the shared e- spend more time near the
Cl nucleus, the Cl side of the molecule has a
partially negative charge
-+
The H side has a partially positive charge
The whole molecule is neutral
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Water Molecule
The water molecule H20 has polar covalent bonds between the O and H.
The shape of the molecule is also important:
It looks like Mickey Mouse
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Water Molecule
The Mickey Mouse shape also makes the molecule polar: The O end is partially negative, and the H end partially positive
+
_
The non-bonding
e- are called
“lone pairs”
XX X
The bonding e-
are called the
“shared pairs”
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Polar Molecules
Just because a molecule contains polar bonds does not mean the molecule itself is POLAR, like water.
C=O=C carbon dioxide has polar bonds between C
and O but the symmetrical shape eliminates the polarity of the whole molecule
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Molecules
Atoms bonded together by covalent bonds form MOLECULES
Molecules are the smallest discrete particle of an element or compound formed by covalently bonded atoms
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Molecules
Each atom in a molecule usually has 8 valence e- (a noble gas e- configuration)
Covalent molecules make up Molecular Substances
Water is a molecular substance
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Molecular Substances
Properties of molecular substances:
1) Soft (like butter)
2) Poor conductors of electricity and heat
3) Low melting points (melt easily)
4) Low boiling points (boil easily)
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Metallic Bonding
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Metallic Bonds
Are a special type of bond between metal atoms of the same element
These bonds are characterized as:
Positive ions (the kernel) immersed in sea of mobile (valence) electrons
The kernel is the nucleus and the non-valence e-
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Metallic Bond: Positive ions immersed in a sea of mobile
electrons
+ + +
+ + +
- --
-
-
-
--
-
- --
-
-
- -
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Metallic Bonds
The valence e- in a metal bond are free to move between the different atoms.
These MOBILE ELECTRONS give metals the ability to conduct electricity and heat
Also the metallic properties of malleabilty and ductility