Background Atoms form bonds (stick to each other) because there are long range a
ID: 3888515 • Letter: B
Question
Background
Atoms form bonds (stick to each other) because there are long range attractive forces that pull the atoms together. However, there are short range repulsive forces which cause the atoms to repel each other when they get too close. A common way to think about this is to imagine the atoms are connected by a simple spring. The spring has a natural length it wants to be at, so if you move the atoms closer than that, the spring is compressed creating a repulsive force. When the spring is stretched, it tries to pull that atoms back together. Either way, the potential energy of the atoms are increased, and they naturally want to move back to the equilibrium position of lowest energy. The following Wikipedia page has a nice description: https://en.wikipedia.org/wiki/Morse_potential (Links to an external site.)Links to an external site.. Read up through the "Potential energy function" portion for a nice description.
Assignment
You decide what the best way to compare them is. Plot the curves in 3D separated from one another on the third axis? Subplots? Two y-axes? All plots in one figure? Metal hydrides in one figure, Hydrogen halides in another? You determine what is best. Be sure to format and clearly label all plots including each curve.
Finally, report any interesting trends you happen to notice, if any, in 750 words or less. If there is a good way to show a trend using a plot, bar graph, etc., do that. Also include the plots of the potentials. For example, are there trends for the dissociation energies or equilibrium separation distances? See what you can find. Upload your MATLAB script as a .m file and your report as a .pdf file.
Background
Atoms form bonds (stick to each other) because there are long range attractive forces that pull the atoms together. However, there are short range repulsive forces which cause the atoms to repel each other when they get too close. A common way to think about this is to imagine the atoms are connected by a simple spring. The spring has a natural length it wants to be at, so if you move the atoms closer than that, the spring is compressed creating a repulsive force. When the spring is stretched, it tries to pull that atoms back together. Either way, the potential energy of the atoms are increased, and they naturally want to move back to the equilibrium position of lowest energy. The following Wikipedia page has a nice description: https://en.wikipedia.org/wiki/Morse_potential (Links to an external site.)Links to an external site.. Read up through the "Potential energy function" portion for a nice description.
Assignment
You decide what the best way to compare them is. Plot the curves in 3D separated from one another on the third axis? Subplots? Two y-axes? All plots in one figure? Metal hydrides in one figure, Hydrogen halides in another? You determine what is best. Be sure to format and clearly label all plots including each curve.
Finally, report any interesting trends you happen to notice, if any, in 750 words or less. If there is a good way to show a trend using a plot, bar graph, etc., do that. Also, include the plots of the potentials. For example, are there trends for the dissociation energies or equilibrium separation distances? See what you can find. Upload your MATLAB script as a .m file and your report as a .pdf file.
Explanation / Answer
Electrons in atoms are placed in zones called ‘orbitals’. In each orbital there is a limit of the number of electrons because electrons are a type of particle called ‘fermion’ which can’t share the same quantum properties. (No-one knows why this is - it’s just the observed behaviour). In some atoms there are orbitals which don’t have all the electrons that could fit. An example is hydrogen. In hydrogen the orbital could fit two electrons, but hydrogen only has one electron.
Because there is space for more electrons, electrons from other atoms can temporarily enter that orbital. For example, if there are two hydrogen atoms, their single electrons can swap back and forth between the orbitals in both atoms.
If you work out the quantum mechanics of two hydrogen atoms with their electrons swapping back and forth, you can find that the overall energy varies depending on how far apart the hydrogen atoms are. The energy is the sum of many things - the repulsion of electrons, the repulsion of the nuclei, and the attraction of electrons and nuclei. Feed all these things in, and you will find that there is a distance at which the energy is lowest. At this distance, the two hydrogen atoms are so close we call them a hydrogen molecule. If you try and move the hydrogen atoms more together or further apart you will need to add energy. This change in energy with distance has a name - it’s called ‘force’.
Atoms which bond this way are said to have ‘covalent’ bonds. The bond isn’t due directly to electrostatic interactions - it’s a quantum-mechanical thing - the sharing of electrons between atoms results in a lowering of energy.
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