Chemistry Buffs I Need Your Help

For molecular geometry you look at the shape of the molecule. For instance CO2 is linear.

I guess electronic geometry means the shape of the e- bonds. if so just say pi or sigma bonds. possibly describe lone pairs. I've never heard that term before.

Polarity you look at electron density and see if it is polar. water is polar because the electron density is not shared equally.


M is Molarity. moles per liter. so 0.09750M is 0.09750 moles per 1 liter.

 

Number 2 is a simple conversion problem.

Like someone said above, Molarity is simply the unit for Moles/Liter so if you are required to make 500.00 mL of .09750 M solution:

.09750 (mole/liter) * .5 (L) * Molecular weight of Sodium bicarbonate (grams/mol) = answer

All units cancel out except grams, which is your mass.

 

yeah basically what i said. Talk about the electron pairs and the bonds in the molecule.

there is more than linear and non linear. You can find them easily, just google the molecule.

 

Google image the compounds or search them on wikipedia. Both very good chemistry resources.

 

Here's a chart to help determine molecular and electron geometry: http://en.wikipedia.org/wiki/VSEPR_theory#AXE_Method

Molecular geometry is solely based on the number of electron groups, meaning it doesn't matter if they're bonding or nonbonding pairs of electrons. Electron geometry, which is the actual "shape" of the molecule, differentiates between bonding and nonbonding pairs of electrons.

For example, the central atom in water, oxygen, has 2 pairs of nonbonding electrons and 2 covalent bonds to hydrogen; thus 4 electron groups, which correlates to a tetrahedral molecular geometry. But since, it has 2 pairs of nonbonding electrons, the actual shape (electron geometry) is bent.

Determining polarity is pretty easy once you have the shape figured out. For water, the oxygen is more electronegative than the hydrogen atoms, making it a polar molecule.



An example of a nonpolar molecule would be CO2, which has a molecular geometry and electron geometry that are both linear. This is because the central atom, carbon, has 2 double bonds to oxygen and 0 nonbonding electrons. Basically, if the central atom has no nonbonding electrons, then the electron geometry is the same as the molecular geometry. The carbon is less electronegative than the oxygen atoms, so there is a polar bond, but since it is a linear molecular, the two polar bonds are orientated in a way such that their directions are opposite of each other, thus canceling each other's polarity out and making it a nonpolar molecule.

 

For Molecular geometry: each of the bonds described represents a pair of electrons. Some atoms in the molecule have lone pairs of electrons. Remember that like charges repel, i.e. the electron pairs repel each other so this is the force that forces the molecule to take a particular shape. So your job is to describe molecule shape based on this.

e.g. NH3 has 3 covalent bonds (3 shared pairs of electrons) and the nitrogen atom has one lone pair of electrons. So, the resulting shape according to your picture is trigonal pyramidal (i.e. the lone pair of electrons occupies the so-called top/point of the pyramid, while the 3 covalent bonds form the 3 legs of the pyramid).

For electronic geometry: basically the same as what I said above; analyze each molecule's electrons and describe where they are located and what bonds they are in, if any.

Google polarity. Wikipedia has a good page too. Basically, it has to do with electron pairs in a molecule not being located right in the middle of the covalent bond; instead it is attracted more towards one of the atoms in the covalent bond. Try and figure out which pairs are more attracted to which atom (if any) and if the overall molecule is 'polarized'. It helps to draw the molecule shape and write in little "delta+" or "delta-" signs as the wiki page shows.

For the concentration question: you need two formulas:
A. "n = c x v" i.e. number of moles = concentration x volume
B. "m = n x Mw" i.e. mass = number of moles x molecular weight

You can figure out how to use the 2 equations to get what you are looking for. To find the molecular weight, simply add the atomic masses of each atom (element) in the molecule.

 

Ummm

 

The subscript tells you how many atoms there are of that element. So for H20, there's 2 hydrogen atoms and one oxygen.

For the number of electrons, read these two:
Valence Electrons
Octet Rule

 

dude you need to just sit down with the book and read. If you are this far behind talking on a forum isn't going to cut it. Read a few chapters and all these questions are answered. None of these concepts have changed in 70 years so any book published in the last few decades will have all of this in it. Wikipedia does also. Just read the stuff.

 

I'm telling you it isn't a problem man. Just read up on wikipedia. I promise you it will be easier to understand than whatever text you will get. These concepts are so old your textbook will not have some special information not available in every other book.

 

Let me make it easy. Here is your reading assignment. Read in this order.


http://en.wikipedia.org/wiki/Lewis_dot

http://en.wikipedia.org/wiki/Molecular_geometry

http://en.wikipedia.org/wiki/Chemical_bond

 

No way, man. You should have learned electron counting in high school, Pun. You don't need a book for that and I doubt you can't google it, dude.

 

I didn't do calculations but i would count off for not havings "mol" or "moles" here.