i need a miracle worker for chemistry...can anyone help me with bonding?

Question

ok i like chemistry but im still bad at it because of a teacher who expects us to know the basics and teaches at an way too advanced level.
now the test is on bonding and i really cant draw the stuff like VSEPR theory and i hope i wrotte the acronym right
like lewis dot i never know if i've got it right and expecially drawing all the bonds.....can anyone explain to me in english so that a dumb person can understand how to draw this stuff and other things is shuld know related to bonding? i don't know this is the first thing thats so hard for me. i feel stupid already so if you're gonna stop by to make me feel even more stupid then dont...only if you have knowledge about chem that you are willing to share in an understandable manner

thanks in advance.

oh wow kentucky your a real genius...thank you so much for that really well though out and informative answer.

Answer 1

OK, lets do this. Lewis Electron Dot formulas and VSEPR (you got it right) - Valence Shell Electron Pair Repulsion theory are used in conjunction to give us an idea of the shapes of molecules. Are these correct? I don't know but doing it this way helps us to predict things like polarity.

First Lewis structures/formulas. These are helpful for molecular species only - not so much good for ionic materials. First add up the total valence electrons for each of the atoms in the formula (valence electrons are the outer electrons available for bonding and are equal to the Group or Family number for the A elements e.g. Na = 1A = 1 valence electron, Cl = 7A = 7 valence electrons, and that’s right, the noble gases have eight valence electrons) remember if the species is an ion add one electron for each negative charge and subtract one electron for each positive charge. Second start to draw the structure by putting the unique element in the center and attaching the other atoms to it by single bonds (2 electrons) and subtract the electrons used for bonding from the total from the first step. Third, distribute the remaining electrons among the atoms trying to apply either the duet rule of giving two electrons to H or the duet rule of giving eight electrons to all other elements. You get into double and triple bonds by trying to satisfy the octet rule. There are some elements that do not obey the octet rule such as B and Be which form compounds that are “electron deficient” and elements such as S that can have more than eight electrons around them.
The part about the Lewis structures we actually need is just the total number of electron pairs around the central atom. Please remember that if you have a double or triple bond, for the purposes of VSEPR we count this as only one pair so that O=C=O would be counted as having only two electron pairs around it. Once you have counted these pairs, you know the geometry of the electron pairs and the geometry of the molecule which takes into account only the groups that are bonded to the central atom. The main idea is that the groups will get as far away from each other as possible, given the constraints of the shape forced on them by VSEPR. So, CO2 would have two groups and this would be linear. BF3 (an electron deficient compound) would have three groups and this would be trigonal planar (flat and three bonds at 120 degrees). If we had a compound/ion that had three electron pairs of which two were involved in bonding and one was a lone pair, that would give a trigonal planar structure that we remove one bonded group from, and the resulting molecule would be bent. For four pairs of electrons, the structure is tetrahedral (like a jack from a jacks game) with bond angles of 109.5 degrees between the groups (example CH4). If we remove one group, the resulting molecule (NH3) will have three bonded groups and a lone pair and that would make it a trigonal pyramid (3 dimensional, not flat). If we remove another group, we have H2O which has two lone pairs and two bonded pairs to give us a bent molecule (and why water is polar rather than non-polar as it would be if it were linear). When you get to 5 and 6 groups around the central atom, please consult your text for the shapes or e-mail me.

Answer 2

Chemistry is a very challenging science, so you are not alone (I felt the same way in the beginning). Don't get yourself down...millions of chem students have felt stupid and thinks their teacher is too advanced.

See the following site for help...gives good summaries as well as practice problems with answers.

http://www.wpbschoolhouse.btinternet.co.uk/page04/4_72bond.htm

Answer 3

email me your questions, I will try to help. Clue: same alias @yahoo.com