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Introduction to Chemical Bonding
Chemical Reactions:• During chemical reactions, elements combine,
rearrange, or break apart with others to form new substances.
• New substances are created when chemical bonds are broken or created.
http://www.polmag.pl/en/media/magnesium.jpg
Magnesium Metalhttp://www.bcscience.com/images/
magnesium_burn.jpg
Chemical Reaction Magnesium Oxide
Original SubstanceNew Substance
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Evidence of Chemical Reactions:
• Fire/Burning• Color change without dye• New gas created• Heat released• Heat absorbed
http://amazingrust.com/Experiments/
background_knowledge/Images/Fire-big.jpg
http://z.about.com/d/chemistry/1/G/5/a/demonstration.jpg
http://www.uncp.edu/home/mcclurem/ptable/ca_2.jpght
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Compounds are more than one kind of element joined together.
Octet Rule: Describes how chemical bonds happen.
• Atoms want a full valence (or outer electron energy level).
• Full valence will mean having 8 valence electrons.
http://www.chemprofessor.com/periodicqm_files/image005.gif
Octet Rule …• To reach full valence, some atoms “want” to
lose electrons and others “want” to gain electrons.– Atoms with FEWER than 4 valence electrons will
bond by losing those electrons.• These atoms will become positively charged!
– Atoms with MORE than 4 valence electrons will bond by gaining electrons (up to eight).
• These atoms will become negatively charged!– Atoms with 4 valence electrons can gain or lose
electrons. It depends on the element to which it is bonding.
It is easier for the atom to lose 1, 2 or 3 electrons rather
than gaining 5, 6 or 7.Why are these atoms positive?
Losing electrons (and electrons are negative) means
more protons (positive charge)than negative charges.
It is easier for the atom to gain 1, 2 or 3 electrons rather
than losing 5, 6 or 7.
Why are these atoms negative?
Gaining electrons (and electrons are negative) means more
negative charge than positivecharges (protons).
A chemical bond is created by the sharing or exchange of electrons between elements.
Example: Sodium (Na)• Valence?
1• Easiest way to follow
Octet Rule?Lose 1 electron
• If following Octet Rule, what’s the charge?
+1
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Example: Fluorine (F)• Valence?
7• Easiest way to follow Octet
Rule?Gain 1 electron
• If following the Octet Rule, what’s the charge?
–1
http://www.bbc.co.uk/schools/gcsebitesize/science/images/
diag_fluorine.gif
What will happen if Sodium and Fluorine atoms are mixed?
• Electrons could transfer between the atoms.• A sodium atom could lose an electron to a
fluorine atom.
• Both atoms are left with full valence & are bonded together, creating a compound.