Reaction Rate Basics

Reaction Rates are affected by a few things. Without telling them the point, the students had a quick demo where they had to dissolve sugar cubes the fastest. 

The things that speed up reactions are:

• Temperature - warmer is faster
• Surface Area - small pieces have more surface area
• Concentration - the more water, the faster sugar will dissolve
• Catalyst - lowers the activation energy and speeds up the reaction
• Agitation - shaking or stirring increases the frequency of collisions.

Le Chatlier

Students learned about reaction rates and how to increase them. They also learned about reversible reactions and how Le Chatlier's principle influences shifts of equilibrium in reversible reactions.

Basically as you apply a stress to a system, the system will shift in response to the stress. If you add one of the molecules it will shift away from that molecule. If you take away a molecule, it will shift towards it to make more. Heat works the same way.

Pressure is the tricky one. If pressure is applied to an equilibrium, then the reaction will shift to the side that has the least amount of molecules (count the coefficients).

Reaction Types

We started by talking about the simple definition of the terms, what the probably products and reactants are and went over a basic formula for the reaction types the students need to be familiar with.

Reaction Types include:

• synthesis
• decomposition
• singe replacement
• double replacement
• combustion
• endothermic
• exothermic
• oxidation-reduction
• neutralization

After discussing the basics, we drew cartoons of stick men and women going on dates to show how atoms move around in the simpler reactions. The picture posted is someone else's version of single replacement (see the one guy switches with the other). For more help with this, check here.

 Homework is to finish the Benchmark Review Sheet and J and I on the orange homework sheet

Balancing Equations

Students are learning to balance equations. Today they learned that reactants are what you start with and are on the left side of the equation. Products are on the right side of the arrow and are what is made by process of a chemical change.

Because of the Law of Conservation of Mass, the number of atoms have to be equal on both sides. To balance an equation, the coefficients are changed. Coefficients are the big numbers in front that tell you how many molecules there are. The subscripts (the little lower numbers) are not allowed to be changed because those are there to make neutrally bonded molecules (what we learned in the last unit.

By changing the coefficients and counting the number of atoms on both sides of the arrow, balancing can be achieved.

Polar vs NonPolar

Anyone who has ever had to share something with someone else knows that sometimes isn't exactly even. Covalent molecules or bonds are no different. 

If a molecules is nonpolar covalent, it is sharing its electrons equally. The best example of this is in diatomic molecules. Diatomic molecules are two of the same atom bonded together - so they would have exactly the same pull. Symmetrical molecules are also nonpolar.

 

Polar covalent bonds occur when electrons are not equally shared. One atom, usually more electronegative, has a stronger pull on the electrons and shares them unequally. The other atom that is less electronegative has a smaller hold on the electrons and is thus can be slightly positive. 

One way to remember this is... "Polar Bears do not share... equally."

Covalent Bonding

The schedule is a little crazy the next couple of days because of the Writing SOL test, but we are practicing ionic bonding and naming and learning how to bond and name things that are covalent. 

If it is a - and -, the bond is covalent. The electrons are shared in the bond. To get the formula, you have to draw the Lewis Dot structures for the elements and connect the dots that don't have friends. You write the formula based on your drawing. To name it, use prefixes to indicate the number of atoms in the formula and the second one ends in -ide. For these it doesn't matter which element comes first.

VSEPR

Valence Shell Electron Repulsion Theory

Electrons do not like each other and when looking at molecular structures - electrons and unshared electrons (the two dots paired together) will space out evenly so they are as far apart as possible.

For help with VSEPR - read this.

Ionic Bonding

Today after a jump in and going over last night's homework, students took a short quiz on these topics (Valence electrons, finding charges, using Roman numerals, counting atoms). I have a feeling they did pretty well :)

Students then learned about ionic bonding. Ionic bonding happens between metals & nonmetals (positives & negatives). The electrons are given and taken in this ionic bond. To get the formula, you criss cross the charges. To name it, you say the name of the metal, then the name of the nonmetal with an -ide ending. If it is a metal from DForP block, then you use a roman numeral to indicate the charge of the metal.

After learning the basics, students in first period practiced with an activity called "speed dating." Students were metals ("boys") and nonmetals ("girls") and practiced dating, bonding, and naming the ionic bonds they would make with their partners. The funny thing is that being a male did not necessarily make your character a "boy." :) Students really got the hang of bonding, were able to work with and help a variety of partners, and had fun. We will continue this activity tomorrow in all class periods.

Now that we understand ionic bonding, students should find this cartoon amusing.

Ionic Bonds for Dummies

Here is a cool interactive where you can build models to simulate ionic bonding.

Tutorial Chemical Formulas

Check out this awesome tutorial about chemical formulas and bonding!


CLICK HERE

Valence Electrons and the charge of ions

Yesterday students learned about valence electrons. Valence electrons are the outermost electrons and are the electrons that are used for bonding and participate in reactions. Valence electrons are only found in the S and P blocks. The max number of valence electrons is 8. Students practiced counting valence electrons and drawing Lewis Dot Structures.

Students also practiced identifying which noble gas an element wanted to be like. All elements want to be like two noble gases - it is just a matter of figuring out which is closer. Elements want to be like noble gases because they have full outer electron shells, or full valences. This makes them stable and non reactive which is why noble gases are sometimes called the inert gases.

Today students learned how to use valence electrons and dot structures to determine the charge of an atom. Atoms either want to gain electrons or lose electrons to become like those noble gases they envy.

• Ions are atoms or molecules that have a net charge, either positive or negative. There are two kinds of ions:
• Anions are negatively charged ions because they have negative net charges. This means that there is a greater number of electrons (-) than protons (+). For example, the anion, fluoride (F ^1-), has a one negative charge because it has a total of nine protons and ten electrons. Thus, the net charge for fluoride is 1 negative.
• Cations are positively charged ions because they have  positive net charges. This is due to these ions having more protons (positive charges) than electrons (negative charges). For example, calcium (Ca 2+) is a cation ion with 20 protons and 18 electrons. The net charge for Calcium is 2 positive. (from here)

Students also learned how to identify the charges of metals with more than one oxidation state using Roman numerals. Metals in the D, F, and lower P get Roman numerals - basically all metals but the S block, Aluminum and Boron get roman numerals. The roman numeral tells you the charge. We have to use this system because those odd metals can actually be found in more than one form - some with 2 possible charges - some with more than four!

Tonight's homework is Box A and E on the orange sheet.
The end of the nine weeks is March 11th.