Quick review: Lewis (electron)Dot
A) What is a Lewis dot diagram• A way to represent the potential reactivity of
an atom without drawing the entire electron arrangement
• A diagram showing the number of valence electrons for an element’s atom
FChemical Symbol
Each dot represents a valence electron
B) How do you know how many valence electrons?
• Look at the group number• Groups 1 and 2, use their number• Groups 13-18, subtract 10 from their number
F 7 dotsFluorine = group 17 Group 7a
Bonding Notes
• Why bond?– Want to fill their outer energy level (octet rule)
– Want to be like the noble gases (they have full energy levels!!)
What are Chemical Bonds
Attraction between two or more atomsInteraction between valence electronsIonic bondsCovalent bondsMetallic Bonds
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Ionic Bonds
• Definition: bond formed between a metal and a non-metal
– If an atom gains or loses an electron it becomes an ion
• An Ion is an atom with a charge (+ or -)• Metals have a tendency to LOSE electrons
(become positively charged).
Why?• Why would an atom want to lose or gain
electrons?– Want to have full outer energy levels– If an atom only has 1 electron in its outer level,
then by losing that electron, its “new” outer level will be full
– If an atom only needs 1 electron to be full then it will gain 1 electron
Li Li
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Examples• Sodium only has 1 electron in its outer
energy level– by losing this electron its “new” energy level
will be full– By losing an electron it loses a negative
charge, thus becoming slightly positive
Examples
• Fluorine only has 7 electrons in its outer energy level– by gaining an electron its “new” energy level
will be full– By gaining an electron it becomes slightly
negative
Examples
• What is Sodium gave it’s electron to Flourine?
• They would make an Ionic bond.
Na F Na+
F-Na F Na+
F-
Losing or Gaining more than 1?
• Elements can gain or lose as many electrons as needed to make their outer energy level full– Magnesium wants to lose 2 electrons
• Mg Mg2+
– Oxygen wants to gain 2 electrons• O O2-
– What happens?• Mg2+O2- making MgO
A general rule
• Groups 1, 2, and 13 like to lose electrons
• Groups 15, 16, and 17 like to gain electrons
Covalent Bonds
• Some atoms are unlikely to gain or lose electrons– Carbon has 4 electrons in its outer energy
level, it would either need to gain 4 or lose 4, how could it ever decide?
– Atoms that don’t gain or lose electrons become more stable by sharing electrons
• A covalent bond is a bond formed between a nonmetal and another nonmetal.