Bonding

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Bonding
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Why do Atoms Bond?

• Atoms bond when their valence electrons interact
• Generally, atoms join to form bonds so that each
  atom has a full outermost energy level.
• Examples Draw the Bohr model for
• Ne F O Li

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6
2
2
2
8
7
1
Give away 1 e
Needs 2 e
Full outer level
Needs 1 e
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Ionic Bonds

• Formed when atoms TRANSFER electrons
• This causes two oppositely charged ions to form
• What is an ion? It is an atom with a charge
• Both ions that form have a filled outermost
  energy level
• The result is a POSITIVE ion and a NEGATIVE ion.

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Calculating Charges of Ions

• Sodium normally has 11 electrons, 1 valence
  electron. It gives it away. It still has 11
  protons, but now has 10 electrons. 11
• -10
• 1 charge
• If an atom loses an electron, its charge is 1
• If an atom loses two electrons, its charge is 2
• If an atom gains an electron, its charge is 1
• If an atom gains two electrons, its charge is -2

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Examples Lithium Fluorine

• Li F
• First, draw the Bohr Model
• Lithium has an extra electron, fluorine needs one
  more
• Lithium gives its valence electron to Fluorine
• Li now has a 1 charge. F now has a -1 charge.
• Oppositely charged ions attract each other and
  form an ionic bond.

3 -2
9 -10
-1
1
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Ionic Bonding Animation (NaCl)

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The Dog Bone AnalogyTaken from
http//ithacasciencezone.com/chemzone/lessons/03bo
nding/dogbonds.htm

• Ionic bonding can be best imagined as one big
  greedy dog steeling the other dog's bone.

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More Facts About Ionic Bonds

• When melted or dissolved in water, ionic
  compounds conduct electricity
• Elements in ionic bonds form COMPOUNDS from a
  METAL and a NONMETAL
• How do you determine metals vs nonmetals?
• Look on your periodic tablethere is a little
  stair step that divides metals from nonmetals
• Elements to the right of this line (including
  Hydrogen!) are nonmetals
• Elements to the left of this line are metals

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Reactivity of Metals

• Reactivity lab think back to the reactivity
  labwhich was more reactive Al or Mg?
• Mg wasit had fewer valence electrons.
• In the case of a METAL, fewer valence electrons
  more reactivebut WHY?
• Metals are trying to get rid of their electrons.
  
• Electrons are attracted to protons. Farther to
  the left on the periodic table, elements have
  fewer protons.
• Fewer protons, less attraction, easier to get rid
  of electrons
• Predict which is more reactive, Na or K.
• Kit has more energy levels.
• The farther an electrons is from the nucleus, the
  easier it is to give away.
• Nonmetals are OPPOSITE from metals

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Covalent Bonds

• Atoms joined by covalent bonds SHARE electrons
• Covalent bonds form MOLECULES
• Made from 2 or more NONMETALS
• In the case of covalent bonds, atoms dont
  transfer electrons because each needs to gain
  electrons

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Examples of Covalent Bonds

• F2
• Both need 1 electron so they share one electron
  each

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Covalent Bonding Animation (Cl2)

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Non-Polar Covalent Bonds

• When both atoms are the same, the electron is
  shared EQUALLY
• Atoms may share more than one pair of electrons
• Examples O2 or Cl2

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The Dog Bone Analogy

• Covalent bonds can be thought of as two or more
  dogs with equal attraction to the bones.  Since
  the dogs (atoms) are identical, then the dogs
  share the pairs of available bones evenly. 

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Polar Covalent Bonds

• When two UNLIKE atoms share electrons, the
  electrons are NOT shared equally
• Electrons are attracted to elements that are
  located farther to the right and closer to the
  top of the periodic table
• The occurs because
• Farther to the right has more protons
• Closer to the top has fewer energy level
• Example CO2

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The Dog Bone Analogy

• These bonds can be thought of as two or more
  dogs that have different desire for bones.  The
  bigger dog has more strength to possess a larger
  portion of the bones.  Sharing still takes place
  but is an uneven sharing. 

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Polyatomic Bonds

• Two or more covalently bonded atoms form an ion
  because they have either gained or lost electrons
• Examples (you do not have to memorize these).
• Hydroxide OH-
• Carbonate CO32-
• Sulfate SO42-
• Nitrate NO3-
• Nitrite NO2-
• Phosphate PO43-
• Hydrogen Sulfate HSO4-
• Cyanide CN-

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Review Questions

• In what type of bond are electrons shared
  equally?
• Nonpolar covalent
• In what type of bond are electrons transferred?
• ionic
• Determine if the following compounds/molecules
  are likely to have ionic or covalent bonds
• MgO
• Ionic (a metal and a nonmetal)
• SrCl2
• Ionic (a metal and a nonmetal)
• O3
• Covalent (nonpolar all the same nonmetal)
• CH4O
• Covalent (polar different nonmetals)
• Explain why electrons are shared equally in
  ozone, O3, and unequally in carbon dioxide, CO2.