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. New Substance Original Substance Magnesium Oxide Chemical Reaction http://jchemed.chem.wisc.edu/JCESOFT/CCA/CCA3/STILLS/MAGAIR/MAGAIR/64JPG48/6.JPG http://www.bcscience.com/images/magnesium_burn.jpg Magnesium Metal http://www.polmag.pl/en/media/magnesium.jpg

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://static.howstuffworks.com/gif/cold-pack.jpg http://en.wikipedia.org/wiki/Self-heating_can http://www.uncp.edu/home/mcclurem/ptable/ca_2.jpg

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

Why are these atoms negative? Gaining electrons (and electrons are negative) means more negative charge than positive charges (protons). 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 gain 1, 2 or 3 electrons rather than losing 5, 6 or 7. 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.

Easiest way to follow Octet Rule? Lose 1 electron 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 http://www.historyforkids.org/scienceforkids/chemistry/atoms/pictures/sodium.jpg

Easiest way to follow Octet Rule? Gain 1 electron 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.