Melting Point and Boiling Point

1. From the brilliant minds of Kevin Kim, Andrew Martuano, Matt Muhs, and Will Grubbe. Melting Point and Boiling Point

2. 1) Definition • Melting Point • The temperature at which the vapor pressure of the solid and the liquid are the same and the pressure totals 1 atmosphere • Layman’s terms- when a substance goes from a solid to a liquid • Boiling Point • The temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid and the liquid changes into a vapor • Layman’s terms- when a substance goes from a liquid to a gas

3. 2) Trends Down a Column • Disclaimer: GENERALLY SPEAKING. There are very few trends for this area of periodicity. • Melting point – For all groups but the alkali metals and metalloids, melting point INCREASES with atomic number • Alkali metals and metalloids – melting point DECREASES with atomic number • Boiling Point exhibits similar patterns

4. 3) Gettin’ Chem-y with it • As atomic number goes up, more protons are present. Therefore there must be an equal amount of electrons present as well. These molecules are attracted to each other, so the more of them that are present, the more energy it takes to break them apart. This raises the amount of energy it takes to cause a phase change in the substance – so, we get a higher boiling and melting point • On the flipside, however, a decrease in melting/boiling point would result in a weakening of bond strength as the atomic number increases. This is because the electrons are getting further and further away from the positive nucleus • Explains both sides of the story

5. 4) Going Sideways • Again, Disclaimer. Not really a definite pattern to be found. • HOWEVER – disregarding the first period (Hydrogen and Helium) • Boiling and Melting point reach a maximum at some point near the middle of the period, and then decrease • Metals + Metalloids = sharp drop • Nonmetals = gradual drop

6. 5) Why this happens • Z*! • Effective Nuclear Charge – increases across a period • Similar logic to the first AP proof- more electrons means greater amount of negative charge all around the nucleus • Makes the forces between atoms stronger, therefore requiring more energy input to change the state of the element

7. 6) Units! • Boiling point AND Melting point measured in regular temperature degrees (Celsius, Fahrenheit, and Kelvin) • Most commonly Kelvin or Celsius

8. 7) Weirdos. • Anything that sublimes/ goes through deposition • Dry Ice, Arsenic – more common in compounds • Highs • Melting Point – nonmetal is Carbon (enormous exception), metal is Tungsten • Boiling Point – Rhenium • Lows • Melting Point – Helium • Boiling Point – Helium • Any element with different structural forms, such as sulfur or oxygen • The majority of the transition metals • In all honesty, much easier to note exceptions than to try and pinpoint a trend

9. However… • What you should pull away is that it generally takes more to change the state of metals then nonmetals. Remember the whole specific heat thing? Result of the bonds within the intermolecular structure that we touched on.

10. Boiling Points!

11. Melting Points!