Introduction
The goal is a fast paced trip through the realm of Chemistry. Appendices at the end of this document will discuss this and also provide more info on topics that in this trek were treated with very thin coverage.
Composition
Let’s go back to a time where people believed that all materials were built from four basic building blocks, earth, wind, fire and water. You could make anything you want by mixing together these four basic things, just like we get green by mixing together blue and yellow.
They were wrong about what the building blocks were but they were right about the notion of composition and building blocks.
Atoms
Next, let’s visit Democritus, who talked about taking a pure something, and dividing it into smaller and smaller pieces of the something until a smallest piece is reached and if you divide that you no longer have the something. He calls that smallest piece an atom. At this point they would be discussing an atom of water.
Electrolysis
Fast forward a few centuries and watch as someone runs electricity through water and discovers that two different gases appear. These can be collected and if you mix them and provide a spark, you make liquid water. People realized they were breaking water into two things and that those things were needed to make water.
Elements
Over time people decide that the two gases are elements (things that are a single thing and it has a smallest possible size). The water thing is called a compound since it is built using more basic materials. The part about a something reaching a point where you can’t divide it further without destroying it (alternately we would say ‘changing its properties’) is still true.
Eventually, after doing chest with gas has the show the quantification, the scientists agree that water, which comes from those two gases, hydrogen and oxygen, is built as a compound containing two of hydrogen and one of oxygen. They use the word ‘atom’ for a piece of oxygen or a piece of hydrogen. The conclusion of a 2 to 1 ratio comes from the results of tests observing the volumes of oxygen gas and hydrogen gas reacted together to form water.
Chemists agree to use single letters, H for hydrogen and O for oxygen, and to use subscripts for counting.
We can apply this to Phosphine, which has three hydrogens and one phosphine.
Molecules
The word molecule is used to signify a specific group of atoms. The words “molecule” and “atom” were used more frequently as people begin to understand more about these two things.
- Two hydrogens and oxygen form a molecule of water
- Three hydrogens and phosphorus form a molecule of phosphine
Scientists begin to play with more and more molecules and atoms, and eventually they say they notice that there are two ways that atoms can bond together.
Ionic Bonding
An atom having a negative charge forms a bond with an atom having a positive charge. This is a little bit like two pieces of magnet coming together because they are oppositely charged.
Covalent Bonding
Two atoms come together but opposite charge isn’t the reason. To explain this we need to look at what people have learned about the basic structure of an atom at this point. They say that an atom is a nucleus of protons and neutrons surrounded by electrons. The mixture of protons and neutrons is like the sun, and the electrons are like the planets.
If there are two atoms that both need more electrons, they can come together and share electrons. The sharing of electrons forms a bond and it fulfills their needs for those extra electrons.
- Hydrogen needs one more electron.
- Oxygen needs two more electrons.
- Phosphorus needs three more electrons.
- Oxygen can share electrons with two Hydrogens.
- Phosphorus can share electrons with three Hydrogens.
Introducing the Phosphine Molecule
The illustration below shows a molecule of phosphine with a phosphorus atom at the center (green), three atoms of hydrogen (red) and a pair of nonbonding electrons (light blue).
Periodic Table
We start with the notion of a wrap around effect. When as a child you were counting from 1 to 100 did it kind of feel that every time you could have number like 21, 31, or 41, etc., that you were, in a way, starting over, or wrapping around?
A scientist looking at all the known elements noticed that he could make things match up if he did a wrap around to the elements.
He devised the periodic table to show this wrap-around effect and how things in the same column of the table show several similarities. There were holes showing in his table and he said this indicated that there were some elements that we hadn’t discovered yet. He was correct.
Placement in the a particular column in the periodic table can answer questions about what type of bonding an atom will use.
Octet Rule
Early on it was noticed that several atoms, such as Carbon, Nitrogen and Oxygen undergo chemical bonding in a way to give themselves eight electrons around them. An atom with six electrons would form two bonds, and thus it would gain two additional electrons, one from each bond.
Hydrogen was an exception in that it would always form a single bond to get one more atom–it was happy with a total of two electrons.
This octet rule explains why oxygen wants two hydrogen’s, phosphorus wants three hydrogens–as does nitrogen, and carbon wants four hydrogens.
Molar Mass
33.99758 g/mol
- H is 1.0079
- P is
Structure
- The P-H bond length is 1.42 angstroms.
- The H-P-H bond angle is 93.5 degrees.
Molecular Symmetry
We can build a model of the phosphine molecule and see that it has an axis of rotation (120 deg) and three planes of reflection that are vertical (tgey include the axis of rotation).
Enthalpy
Enthalpy of formation of gas at standard conditions (298.15 K, 1 atm): 1.31 kcal/mol
Entropy
Entropy of gas at standard conditions (298.15 K, 1 bar) 50.249 cal/mol*K
Elsewhere, Standard Molar Entropy was reported as 210 J/mol*K
notice the switch from kcal to cal as we go from enthalpy to entropy and also noticed that the units for pressure changes from atmospheres to bars.
Appendix A
There is an idea that if we have two different things in the gaseous state, and they are both in the same volume at the same pressure and the same temperature, then the count of the number of particles will be the same. Another way of saying this is that it doesn’t matter what it is, is it just matters how many there are.
To the best of my knowledge, so far, this was something they didn’t prove, they used it (correctly) as a postulate.
Appendix R – References
The following page offers indications that the Phosphine isn’t present in Venus, and there was a procedural error in the analysis.
Rob Sterling 