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

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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.