Unit Three Biochemistry

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Unit ThreeBiochemistry HomeostasisChemical
Bonding
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I. Bonds are the forces that hold atoms together

• We are going to learn about intramolecular forces
  forces within molecules
• Intramolecular forces include
• covalent bonds
• ionic bonds
• metallic bonds

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2 Types of Bonds

• A covalent bond is formed when two atoms share
  electrons to become a stable molecule/compound
• An ionic bond is formed when ions are attracted
  by their opposite charges and transfer electrons

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Bonds continued

• In both cases, the atoms ultimate goal is to have
  a stable e- configuration
• Atoms are considered stable if they follow the
  Octet Rule
• ? atom must have 8 valence e- to be stable
• Exceptions ? H and He only need 2 valence e- to
  be stable

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Valence Electrons

• What are valence electrons?
• Valence electrons are the electrons in the last
  shell or energy level of an atom
• A quick way to determine the of valence
  electrons is to look at which group the atom is
  in

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Valence Electrons

• Elements in group 1 have 1 valence electron. 
• Elements in group 2 have 2 valence electrons. 
• Can you guess how many valence electrons elements
  in group 6 have? 
• If you guessed 6 valence electrons, then you are
  correct!

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Valence electrons

• Look at your periodic tables
• The Nitrogen atom has 5 valence electrons
• Why?
• What group is Nitrogen in?
• Group 15

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Valence Electrons

• The Oxygen atom has 6 valence electrons
• Why?
• What group is Oxygen in?
• Group 16
• Do you see the pattern?

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Electron Orbitals (Energy Levels)

• These pictures show the electron orbitals of
  Nitrogen and Oxygen
• 1st orbital 2 electrons max
• 2nd orbital 8 electrons max

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Pop QuizAre Nitrogen and Oxygen stable?

• No!
• Why not?
• They do not follow the Octet Rule

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Pop QuizWhat is the Octet Rule?

• The Octet Rule states that atoms must have 8
  valence electrons to be stable ? except for H and
  He.

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II. Ionic Bonds

• Atoms that lose/gain electrons become ions
• ? charged particles
• Bonds form when ions are attracted to each other
  by their () and (-) charges
• A valence electron from one atom is transferred
  to another atom

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More on Ionic bondsMetals vs. Nonmetals

• METALS
• Lose electrons
• Become positive ions
• Sodium ion Na 1

• NONMETALS
• Gain electrons
• Become negative ions
• Chlorine ion Cl -1

How do you know which elements are metals and
nonmetals?
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Metals vs. Nonmetals

• The ladder divides the metals from nonmetals

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III. Covalent Bonds

• Strong attractions that hold nonmetallic elements
  together Ex. HCl, CO2
• Associated with a great variety of materials
• found within elements, compounds, molecules and
  diatomic molecules

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Covalent Bonds cont

• Diatomic molecules are formed when 2 of the same
  atoms combine
• Ex. O2, H2, F2
• Both atoms have an equal attraction to the shared
  electrons
• Co means to share, think of other co words

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Covalent Bonds cont

• The shared electrons count for both atoms
• Single covalent bonds share 2 e-
• Double covalent share 2 pairs of e- 4
• Triple covalent share 3 pairs of e- 6
• Count all bonds to determine if the octet rule is
  satisfied or not

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IV. Lewis Diagrams

• A Lewis Diagram consists of the element symbol
  surrounded by "dots" to represent the valence
  electrons.
• It is also used to model the transferring/sharing
  of electrons during bond formation

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Lewis Diagrams

• Draw the following diagrams in your notes
• Which group is each element in?

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Lewis Diagrams

• The electron dot diagram for O shows two unpaired
  electrons, so it has two electrons available for
  standard covalent bonds.

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Lewis diagrams

• Lewis diagrams can show how atoms combine
• When atoms form diatomic molecules we will see
  single, double, triple covalent bonds
• Single covalent bonds (share 2 e-)
• H2 ? HH single covalent bond
• A dash between two atoms is sometimes
• used to show single bonds ? H-H

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More Lewis diagrams of compounds

• Single covalent bonds continued
• Halogens (group 17 atoms) also share 2 e-and form
  single covalent bonds
•      Cl Cl
      
• Count the electrons does each atom have a
  complete octet?

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More Lewis diagrams of compounds

• Double covalent bonds (share 2 e- pairs)
• Ex.       O O
       
  
• Count the electrons does each atom have a
  complete octet?
• Triple covalent bonds (share 3 e- pairs)
• Ex. N N

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Lewis diagrams of compoundsFinal Thoughts

• The Octet Rule and Lewis diagrams
• When drawing diagrams of compounds remember the
  Octet Rule ? each atom must have 8 valence e- to
  be stable
• Exceptions ? H and He only need 2 valence e- to
  be stable