Question from a reader: Rank the compounds NH3, CH4,PH3 in order of increasing boiling point. Explain your answer.
Question from a viewer: Water, H2O, boils at 100 degree Celsius ; ethanol, C2H5OH, boils at 78 degree Celsius, and ammonia NH3 boils at -33 degree Celsius. Rank these three compounds in order from weakest to strongest intramolecular interaction. Explain how you get your answer.
Higher boiling point = stronger intermolecular forces.
Water boils at a higher temperature because its hydrogen-oxygen bonds cause hydrogen bonding, which is a strong intermolecular force that makes the molecules stick to each other. This means you have to add more energy (heat) to get them to separate and boil.
Question from a viewer: For each of the following pairs of atoms, write a likely formula for a simple compound made from them, and indicate if the bonding is ionic or covalent.
A) Ca & Cl
B) S& H
C) Cl & N
D) Fe & Br
Ca and Cl --> Ca is a metal, Cl is a non-metal, therefore they are IONIC together
Video of me drawing the diagram to connect the two: https://www.youtube.com/watch?v=8aDXuwsDxWE
S and H are both non-metals --> they are COVALENT together.
S brings 6 valence electrons and needs two more. H brings one each, so you need TWO hydrogens to bond with ONE sulfur --> H2S
Cl and N are both non-metals --> they are COVALENT together.
N has 5 valence electrons and needs 3 more. Each Chlorine shares ONE and so you need THREE chlorines --> NCl3
Fe is a metal and Br is a non-metal --> they are IONIC together.
This one is tough unless you know (or have a periodic table that tells you) that Fe can have charges or either +2 or +3.
+2 charge --> FeBr2
+3 charge --> FeBr3
A question from a viewer: How do we find the difference between molecules and compounds? I know that all compounds are molecules, but not all molecules are compounds, but how do we find the difference by just looking at a given atom? ex: O2, O3, CO2, etc. Thank you!
A molecule is anything made of 2 or more atoms
O2 is a molecule because it is made of 2 atoms
O3 is a molecule because it is made of 3 atoms
CO2 is a molecule because it is made of 3 atoms
A compound is anything made of 2 of more ELEMENTS
O2 is NOT a compound because it is only made of oxygen
O3 is NOT a compound because it is only made of oxygen
CO2 IS a compound because it is made of carbon and oxygen (2 different elements)
One question that leads people to my website more often than any other ...
Question: Calculate δHrxn for the following reaction: c(s)+h2o(g)→co(g)+h2(g)
use the following reactions and given δh values:
c(s)+o2(g)→co2(g), δh= -393.5 kj
2co(g)+o2(g)→2co2(g), δh= -566.0 kj
2h2(g)+o2(g)→2h2o(g), δh= -483.6 kj
This is a classic Hess' Law question. Your job is to rearrange the three given reactions so that they add up to (and cancel to) the target reaction.
Keep Reaction 1 as is.
Reverse Reaction 2 and cut in half.
Reverse Reaction 3 and cut in half.
c(s)+o2(g)→co2(g), δh= -393.5 kj
co2(g)→co(g)+0.5 o2(g), δh= +283.0 kj
h2o(g)→h2(g)+0.5 o2(g), δh= +241.8 kj
Total enthalpy: -393.5 + 283.0 + 241.8 = +131.3 kJ
Edit, in August 2020: I have decided to answer questions like this one on a new site, www.lewis-structure.com. This molecule in particular was made into my first post, which is at http://lewis-structure.com/ch3f-lewis-structure-and-ch3f-hybridization/