Bonding

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Bonding
February 11-12, 2008
Objective Demonstrate understanding of Borhs
model to show how ionic compounds are formed
Bellwork What does bonding mean?
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Sodium chloride (table salt)
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Bond Types

• We have been talking about atomic structure, now
  we are going to focus on molecules
• To understand how molecules are formed we need to
  review and know very well Bohrs atomic model

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Bohrs Model

• Neutrons and protons () occupy a dense central
  region called the nucleus.

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Bohrs Model
Electrons (-) orbit the nucleus and are grouped
into units called shells.
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Bohrs Model
Electrons (-) fill up shells as follow 2, 8, 8,
18, 18, 32,32
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Bond Types

• Atoms form chemical bonds.
• A chemical bond is an electrostatic force of
  attraction between atoms.
• There are 2 types of bonding ionic, covalent
• From ionic stealing of electrons to form
• and ions. and then attract
• Covalent sharing of electrons

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Ionic bonding

• Ionic bonding involves 3 steps
• 1) loss of an electron(s) by one element,
• 2) gain of electron(s) by a second element,
• 3) attraction between positive and negative

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• Atoms bind together because it makes them more
  stable
• The result of the chemical bond is
• a valence shell completely full.
• Similar to the electron configuration
• of a noble gas
• All elements want to be just like
• noble gases!!!

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Reviewing

• A chemical bond is an electrostatic force of
  attraction between atoms.
• In an ionic bond an element looses an electron
  and another element
• gains the electron.
• In an ionic bond the molecule is held together
  due to the attraction of the positive and
  negative charges.
• We can use Bohrs model to represent ionic bonds.

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Bonding
February 13-14, 2008
Objective Demonstrate understanding of Borhs
model to show how ionic compounds are formed.
Show how covalent bonds are formed.
Bellwork What are the steps involved in Ionic
bonding? Please fill up the missing words
1) ____ of an electron(s) by one element, 2)
____ of electron(s) by a second element, 3) ____
between positive and negative
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Ionic Bond

• Ionic Bond electrons are given and taken when
  chemical bonds are formed. The atoms become
  positive or negative, and are attracted to each
  other.

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Ions

• Ion An atom with a different number of
  electrons.
• Anion a negative ion has more electrons than
  normal
• Cation a positive ion has fewer electrons than
  normal

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• Covalent Bond electrons are shared when
  chemical bonds are formed.

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Covalent bonding

• Just as with ionic bonds, covalent bonds must
  involve a net lowering of energy
• We can explain this net lowering of energy in two
  ways
• 1) visualizing the combination of attraction as
  two atoms approach each other
• 2) drawing and combining orbital diagrams

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As atoms approach

• The attraction for electrons is not limited to
  free electrons, but also involves electrons that
  are part of other atoms.

• Thus, atoms are pulled toward each other
• How far they are pulled together will depend on a
  balance of attraction (nucleus to electrons) and
  repulsion (nucleus to nucleus and electrons to
  electrons)

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Bond Types

• What causes atoms to form molecules?
• Basically, all things that happen spontaneously
  are energetically favorable (a book dropping)
• You never see a book spontaneously rise
• Something must be energetically favorable about
  atoms coming together as molecules
• Today we will look at ionic bonding