The Octet Rule

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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)
• Cl

H
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When does covalent bonding occur?

• Between elements that are non metals
• 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
• 1.1
• Since 1.1 is less than 1.7, this bond is covalent

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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.

O
O
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
O
O
Double bond
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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• 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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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
-

H
Cl
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
_
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Polar Molecules

• Just because a molecule contains polar bonds does
  not mean the molecule itself is POLAR, like
  water.
• COC
• 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
• Soft (like butter)
• Poor conductors of electricity and heat
• Low melting points (melt easily)
• 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 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