Author Archives: hangtime

VSEPR Theory

Of all the words in this acronym -- Valence Shell Electron Pair Repulsion -- the one we'll be emphasizing is repulsion, since that's really the meat of it. Using foam models and a few poodle analogies, we'll show you what the heck trigonal, pyramidal, planar, tetrahedral, bent, octahedral, and lone pair central atoms really mean!

This video appears on the page: Molecular Shape & VSEPR Theory

Molecular Shape & VSEPR Theory

In this chapter we use Valence Shell Electron Pair Repulsion, or "VSEPR", to figure out what shape molecules will have based on their Lewis Structures.

Part of the course(s): Chemistry-General

Solving Rational Equations
(x in denominator)
Solving Rational Equations (x's in denominators)
Rate/Time Word Problems Using Tables
Working Together" Rate/Time Word Problems

Rational Equations are the problems where you have a bunch of x's and x2's in the denominator of a giant fraction, and you have to find the least common denominator and simplify in order to solve for X.

Part of the course(s): College Algebra

Resonance Structures

When a Lewis structure requires a double bond, you've probably wondered to yourself, "Which bond should I make double?" Good question. Lewis makes you pick one, but it turns out the truth lies somewhere in between a single and double bond, as explained in this lovely video.

This video appears on the page: Lewis Dot Structures

Lewis Structures Of Ions

These are really similar to Lewis structures of molecules, except the ionic charge gives you a couple extra (or fewer) dots to play with in your Lewis structure. Also, your teacher may or may not want you to draw giant brackets around your answer.

This video appears on the page: Lewis Dot Structures

Exceptions to the Octet Rule of Lewis Structures

Almost every atom is super-happy to have eight valence electrons, but there are exceptions that most teachers will expect you to know, and which can wreak havoc on your Lewis Dot Structres. Boron, just six? Sulfur, 12? You're crazy!

This video appears on the page: Lewis Dot Structures

Lewis Dot Structures of Molecules

Single bonds, double bonds, triple bonds: this video covers about 80% of the Lewis dot structure problems you're likely to see. Teachers tend to make these seem super-hard, but as with most topics, once you see me lay out the step-by-step process that will work every time, you too will wonder why your teacher didn't just teach it this way in the first place!

This video appears on the page: Lewis Dot Structures

Valence Electrons & Lewis Dot Structures of Atoms

This video covers Lewis dot structures of single atoms, as well as how to calculate the number of valence electrons using the periodic table. There are two slightly different methods of writing these. I cover both, but before your first quiz you should as your teacher exactly how they want these single-atom Lewis dot structures done so you don't lose any points doing them the "other" way.

This video appears on the page: Lewis Dot Structures

Lewis Dot Structures, Valence Electrons &
Resonance Structures

This chapter covers Lewis dot structures of atoms, ions, molecules, and polyatomic ions.

Part of the course(s): Chemistry-General

Calculating Molecular Formula From Empirical Formula

You won't usually see this type of problem on its own -- it's usually just a step in a longer problem -- but since those longer problems always tend to be super tricky, it's a good idea to master this step first.

This video appears on the page: Empirical Formulas

Finding Molecular Formula Using Percent Composition

These are the big nasty word problems we've been building towards. They look super-hard when you first see them, but by breaking them down into the step-by-step process in this video, most students end up looking forward to these on the test as "easy" points. Compared to Stoichiometry, anyways!

This video appears on the page: Empirical Formulas

Calculating Empirical Formula of a Compound

This video explains what the empirical formula of a compound is, and how to find it based on the molecular formula. An important first step!

This video appears on the page: Empirical Formulas

Empirical Formulas
Calculating Empirical Formula of a Compound
Calculating Molecular Formula From Empirical Formula
Finding Molecular Formula Using Percent Composition

How to find an empirical formula, how to derive a molecular formula from the empirical formula, and how to find molecular formula from percent composition.

Part of the course(s): Chemistry-General

Common Compounds You Must Memorize

Ever accidentally call H2O "dihydrogen oxide" or wonder why everyone else in your class seem to know the significance of "graphite" and "mother eats peanut butter"? Behold.

This video appears on the page: Naming Compounds

Names of Acids

On the bright side, acids are easy to spot because they all start with H and end with "acid". However, the names are kind of weird other than that: -ic, -ous, hydro-... This video covers the rules for all that so you can ace your acid naming quiz.

This video appears on the page: Intro to Acids & Bases ,Naming Compounds

Naming & Balancing Ionic Compounds

These are more complicated than naming covalent (molecular) compounds. You have to know your polyatomic ions, and you have to know the charge of your mono-atomic ions (click here for review), and you have to know how to "balance" the formula so that it's net charge is zero. Yay, another way to lose points the rest of the year.

This video appears on the page: Naming Compounds

Naming Covalent Compounds

This video has all the rules and numerical prefixes you'll need to name molecular compounds, as well as the tricks for coming up with the formulas when they give you the name. Also covered are a couple important mistakes to avoid with these!

This video appears on the page: Naming Compounds

Naming Compounds
Naming Covalent Compounds
Naming & Balancing Ionic Compounds
Names of Acids
Common Compounds You Must Memorize

Formulas and names of covalent compounds, names and balancing formulas of ionic compounds, names of acids, and common compounds you should know like Mother Eats Peanut Butter.

Part of the course(s): Chemistry-General

Ionic vs Covalent Bonds

These are the two types of bonds that you'll see again and again throughout the rest of chemistry, so it's important to understand what they're all about so that you can follow along when it's time to do stuff to them in later chapters. Balancing net ionic equations, anyone?

This video appears on the page: Types of Bonds

Types of Bonds
Ionic vs Covalent Bonds

An explanation of the two types of bonds which can hold atoms together: ionic and molecular (covalent).

Part of the course(s): Chemistry-General