The size of the non-polar particles (atoms or molecules) involved in the London Dispersion Force has a large effect on the force of the attraction.
Specifically, the larger the molecules, the stronger the force. This can be seen in the following diagram. (In this diagram NPP stands for non-polar particle, and the blue circles and ovals are the electrons.)
The larger particles allow for more "sloshing" of electrons (there is more
room to slosh and generally more electrons to do the sloshing) and
therefore a larger separation of charges.
That means that the positive is more positive and the negative is more negative. As a result the attraction between them is stronger.
This effect can be seen in the different states of the halogens. We know that as we go down the periodic table atoms get bigger. This means that chlorine is bigger than fluorine, that bromine is bigger than chlorine, etc. It follows that Cl2 is bigger than F2 and the Br2 is bigger than Cl2, etc.
If we look at the states of matter we see that F2 and Cl2 are both gases at room temperature, meaning that the attractive force between them is relatively weak. Br2, however, is a liquid at room temperature, meaning that the attractive force between bromine molecules is strong enough to hold them together. Lastly, I2 is a solid, meaning the attractive force can lock the molecules together in a crystal.
So, as the atoms (and therefore the molecules) get bigger, the attraction gets stronger and the state of matter found at room temperature changes from gas (with the least particle to particle attraction) to solid (with the most attraction).
That means that the positive is more positive and the negative is more negative. As a result the attraction between them is stronger.
This effect can be seen in the different states of the halogens. We know that as we go down the periodic table atoms get bigger. This means that chlorine is bigger than fluorine, that bromine is bigger than chlorine, etc. It follows that Cl2 is bigger than F2 and the Br2 is bigger than Cl2, etc.
If we look at the states of matter we see that F2 and Cl2 are both gases at room temperature, meaning that the attractive force between them is relatively weak. Br2, however, is a liquid at room temperature, meaning that the attractive force between bromine molecules is strong enough to hold them together. Lastly, I2 is a solid, meaning the attractive force can lock the molecules together in a crystal.
So, as the atoms (and therefore the molecules) get bigger, the attraction gets stronger and the state of matter found at room temperature changes from gas (with the least particle to particle attraction) to solid (with the most attraction).
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