Author Archives: hangtime

Mass Number Notation

This is what you call it when -- usually in the isotopes chapter -- atomic symbols have little numbers on the left which are the atomic number and mass of the atom. This video covers the common types of problems your teacher might ask, and helps you avoid the most common mistake students make with mass notation.

This video appears on the page: Isotopes & Mass Numbers

Isotopes & "Table Problems"

This video explains what isotopes are, and it features tons of examples of the main type of problem that teachers give you for isotopes: giving you a big table that asks you to figure out the number of protons, neutrons, electrons, and the mass of an atom.

This video appears on the page: Isotopes & Mass Numbers

Isotopes & Mass Numbers

This chapter explains isotopes, the most common problem types, and percent composition.

Part of the course(s): Physics ,Chemistry-General

Bohr's Model of the Atom

The basis of quantum mechanics, Bohr's model created the concept of energy levels in the atom, where each electron is in either one orbital or another but never in between. It explains much of the behavior of atoms, and is the basis of more advanced topics such as emission and absorption spectra, as well as electron configurations.

This video appears on the page: History of Atoms

Rutherford's Gold Foil Experiment

This particular experiment is covered by every chemistry teacher because it invalidated the plum pudding model and demonstrated that an atom's protons are all together in a clump. If your teacher is the type to ask a short answer question on tests, this could be the one.

This video appears on the page: History of Atoms

Plum Pudding Model of Atoms

Up until the late 1800's, scientists starting with Dalton thought there were these tiny things called atoms that were the smallest anything could be. Around 1900 experiments started showing the existence of electrons, then protons. The puzzle was, how do you get a bunch of protons that repel each other to co-exist in an atom? Enter the reasonable, but ultimately incorrect, Plum Pudding theory.

This video appears on the page: History of Atoms

History of Atoms

The history of how scientists figured out that these things called "atoms" consist of a clump of protons with electrons orbiting: Rutherford's Gold Foil Experiment, "plum pudding" model, and Bohr.

Part of the course(s): Physics ,Chemistry-General

Gas Stoichiometry

This chapter covers a molar volume shortcut you can use for stoichiometry when your reactants are all gases.

Part of the course(s): Chemistry-General

Gas Stoichiometry Problems

Stoichiometry with gases can either be really hard, or really easy, depending on whether you remember to use the shortcuts in this video. If you watch this video, you'll never use the ideal gas law to do stoichiometry again.

This video appears on the page: Gas Stoichiometry

Dalton's Law of Partial Pressures

Usually these problems are easy to spot because they have the words "partial pressure" in them. But there are harder to spot types too, so in this video I show you how to spot them and how to solve them.

This video appears on the page: Partial Pressures

Dalton's Law of Partial Pressures

This chapter explains partial pressures, and works the most common types of problems.

Part of the course(s): Physics ,Chemistry-General

STP Gas Problems

From now on you should associate the letters STP with the conversion factor 22.4 liters per mole, a shortcut for ideal gas law problems that take place at "standard temperature and pressure" (STP).

This video appears on the page: Gas Laws

Ideal Gas Law

Let's face it, PV=nRT. 'nuf said.

This video appears on the page: Gas Laws

Combined Gas Law

I know the chapter listing said we'd cover Boyle's Law, Charles' Law and Gay-Lussac's Law. But the truth is you don't need those because the Combined Gas Law is based on them (they're what it's "combining"), thus it can be used for every problem those other laws can be used for using the simple method I demonstrate in this video.

This video appears on the page: Gas Laws

How To Spot Ideal vs Combined Gas Law Problems

When you take the test on the gas laws, the hard part isn't going to be the plug-and-chug. The hard part is going to be figuring out which equation ("law") to plug-and-chug into. So before we get into the laws themselves, this video shows you the quick way to figure out quickly which equation you should use on each problem.

This video appears on the page: Gas Laws ,free videos edit ,Free Sample Videos ,chemistry free videos

Gas Laws

Ideal Gas Law, Combined Gas Law, Boyle's Law, Charles' Law, Gay-Lussac's Law, and how to tell them apart.

Part of the course(s): Physics ,Chemistry-General

Rates of Effusion & Diffusion

This is pretty much the only type of problem you'll see about effusion and diffusion. Using an equation with a giant square root, we can compare how fast molecules (or atoms) of two different gases will wander around, based on the ratio of their molar weights.

This video appears on the page: Effusion & Diffusion

Effusion & Diffusion

This topic almost always comes in the form of questions about the rate of effusion and rate of diffusion.

Part of the course(s): Physics ,Chemistry-General

Molar Volume & Density

This video is for a very specific type of problem which some teachers use, which takes advantage of the fact that at STP, one mole of any gas will occupy 22.4 liters. This is a good skill to have, even if your teacher doesn't put "molar density" in the syllabus.

This video appears on the page: Intro to Gases

Units of Pressure, Volume & Density

This video explains what pressure is and how to calculate it, and it explains why "millimeters mercury" is a reasonable unit of pressure. We'll also cover how to convert between all the crazy units of pressure, including torr, mm Hg, Pascals (Pa), kPa, psi, and atmospheres (atm).

This video appears on the page: Intro to Gases