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Covalent Bonding
1/19/12
• Objective: To explore multiple covalent bonding
• Do Now: On a sheet of paper, write the definition of an ionic bond and a covalent bond. (4 min)– For each kind of bond, give an example of a
compound held together by those bonds.
• Do Later: Finish covalent bonding challenge puzzles
Covalent bonds
• Bonds in which two atoms share a pair of valence electrons.
• Two or more atoms held together by covalent bonds form a molecule.
H
H2
H
Octet rule revisited• Recall: The purpose of bonding is to acquire a
full valence shell– Ionic bonds: NaCl
– Covalent bonds: H2O, CH4
Double bonds
• Two atoms can share more than one covalent bond
• In a double bond, two pairs of electrons are shared
Triple bonds
• In a triple bond, three pairs of electrons are shared
Triple bond (N2)
Bonding Capacity• In each covalent bond, an atom – 1) shares a valence electron with its partner– 2) gets a new valence electron shared with it.
• Atoms need to have at least one of their own valence electrons for every covalent bond they form.
Single bond
Practice problem
• How many valence electrons does boron have?
• What’s the maximum number of covalent bonds boron can form?
Practice problem
• Can boron ever achieve a valence octet by covalent bonding?– No!
Bonding capacity
• For each covalent bond an atom forms, it must have an empty space in its valence shell to receive a new electron.– Fluorine has one empty space in its valence shell,
so it can only form one covalent bond
Practice problem
• What is the maximum number of covalent bonds the following elements can form? – Chlorine– Oxygen– Bromine– Nitrogen– Polonium
Bonding capacity
• The bottom line: – For each covalent bond an atom forms, it must
have:1) A valence electron to share and 2) a vacancy in its valence shell to accept a new electron.
Practice problem
• Fill in this table in your notes: Element Atomic # Valence e-s Vacancies in
valence shellBonding capacity
Hydrogen 1
Carbon 6
Nitrogen 7
Oxygen 8
Ammonia Water
Methane
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