Homework Troubles...><

Okay, my teacher wants us to tell him how to tell him how you can figure out what state a molecular compound will be when you're writing out the formula. Like how you'd say that ionic compounds are always solids when not in a solution...only how do you tell that with a molecular compound?


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this is the

this is the problem:
calculate the masses of N,H, and O in NH3OH if the copositon weight is 2.0g

my answer:

MM:(molar mass)

equals==34.04g NH3OH

percentage of compostion:


O=2.0g (0.47)=0.94g


2 is the answer (according to my solution)

is this correct........?????

Inorganic: Usually abt

Usually abt electronegativity difference
--> molecular or ionic.
e.g. molecular: TiCl4, SnCl4, PCl5, PF5, SF6, H2O
e.g. ionic: FeCl3, NiBr2, NaCl, RbI, LiF, CaCl2.
some groups in inorganic compounds almost certify that they are ionic, e.g. sulphate, nitrate...
for molecular, state determined by:
- shape of molecule, e.g. gas: SF6, UF6 (extreme examples); liquid H2O, HF, TiCl4, SnCl4, GeCl4 (spherical + large size --> polarization of e-; or hydrogen bonding + small size); solid: larger size still, e.g. BI3, NI3, PBr5(ionic).
- structure: long chain: solid: S8, P4, graphite...
for ionic, usually solid.

functional group affects most, though long hydrocarbon tends to being solid.
functional group --> intermolecular forces:
-dipole-dipole interactions: e.g. RCN, RNH2, R2CO
much like magnet + magnet
-inductive forces (permanent dipole - induced dipole)
much like magnet + iron : permanent dipole as above,
induced dipole from easily polarized e- cloud, e.g. benzene ring,
alkene pi bond.
-dispersive forces (instantaneous dipole - induced dp)
weakest, between polarizable e- groups, also in inorg. such as between layers of graphite / iodine / CO2 molecules in solid.
increases with molecular SIZE (not necessarily mass), SA/V (surface area to volume ratio)

but usually typical examples are taught in lesson and most usually the concept is built from the examples, rather than using the concept to predict compounds.
i mean, usually it is hard to predict. Normally an "explanation" is made up to account for a certain phenomenon in chemistry.
provided your standard from the level of your question, you shall learn more of this when it comes to trends, across periods / down groups. changes in density, mp. bp., liquid range, hardness, mp bp or compounds, solubility of oxides, hydroxides, chlorides...
you remember the reasons and apply to unfamiliar examples and HOPE that it works. If it doesn't, make up another reason (or "factor"). usually all factors are taught before such questions.

jose balance the following

balance the following equations:
1. Li(s)+N2(g)
2. La2o3(s)+H20(l)
3. NH4N03
4. Ca3P2(s)+ H20(l)
5. Ca(OH)2(aq)+ H3PO4(ag)
6. AgNO3(aq)= Na2SO4
Can someone show how to balance these formulas?

Well, you find the typical

Well, you find the typical valencies of each species and then conserve mass and charge. To take example 6:

Ag(NO3)(aq) + Na2SO4 (aq)
you would have 1) Ag+ + 1) NO3- + 2) Na+ + 1) SO4=

that means that to match the 2 pluses of the Na, you must have 2 minuses from NO3-, so you double that, but then you have to double the Ag+, but that's OK because you have 2 minuses with the SO4=, so the balanced equation is would be
2 Ag(NO3)(aq) + Na2SO4 (aq) -> Ag2SO4 (s) + 2 Na(NO3) (aq)

Helpful stuff for homework

Helpful stuff for homework troubles.

give example.

Water, or any molecular compound. When you write out the formula, how do you know if it's gonna be solid, liquid or gas?

You just look it up :)

[color=darkgreen]Well, with water, it implies liquid. Water [b]vapor[/b] would imply water in the gas phase and ice would imply that the water is solid.

Most of the time, if it is needed in the problem, you should be given sufficient information to figure it out. They may give you the temperature and that can tell you what phase it is in or (I'd hope) that they would tell you.

If it's at STP (standard temperature and pressure), then you can look it up- either online or in a table, which you should be able to find fairly easily. At room temperature, most of the molecules in the periodic table are solids, but some are gases. Most metals and metal compounds are solid at STP, while non-metals and non-metal compounds (like sulphur dioxide or water) tend to be liquid or gas at STP.

Hope this helps. :)[/color]

Figuring out the physical state of a molecular compound at STP given only its chemical formula usually isn't easy. There are several things to consider:

-What is the molar mass of the molecule? Molecular compounds with high molar masses are typically solids or liquids. This is because such molecules have a large number of electrons and thus experience much stronger intermolecular forces. Tungsten hexafluoride has the highest known molecular weight (298) for any gas at STP. So any molecular compound with a molar mass higher than this will be either a solid or liquid, but not a gas.

-Does the compound participate in hydrogen-bonding? If so, then it is most likely a solid or liquid. This is because hydrogen-bonding is a very strong intermolecular force. One of the few gases that hydrogen-bond is ammonia. Hydrogen bonding can be inferred from some formulas like C6H5OH. I can't think of any gas that participates in hydroxyl group-based hydrogen bonding though, so any molecule with a hydroxyl group can probably be said to be solid or liquid at STP.

WebElements: the periodic table on the WWW [http://www.webelements.com/]

Copyright 1993-20010 Mark Winter [The University of Sheffield and WebElements Ltd, UK]. All rights reserved.