Thursday, September 27, 2012

Polar and NonPolar Covalent

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."

Friday, September 21, 2012


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.

Most of the names of the shapes of hints like tri, tetra, planar, etc. Students need to memorize these shapes and be able to visualize them for given formulas.

For help with VSEPR - read this.

Thursday, September 20, 2012

Covalent Bonding

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.

Wednesday, September 19, 2012

Ionic Bonding

Students 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.

Tuesday, September 18, 2012

Metals = Roman Numerals

Time to learn about roman numerals.... Here is a handy clock if you are unfamiliar with them. Pretty much you need to know 1-7. 1 is represented with I, five with V and 10 with X.  4 and 6 and 7 is where it gets tricky. 4 is 1 before 5 - so its Roman numeral is IV. 6 is one after five so its roman numeral is VI.

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!

Monday, September 17, 2012

Valence Electrons and the charge of ions

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)

Friday, September 14, 2012

Formula Writing

Today we discussed how to write chemical formulas, and what the numbers associated with a chemical formula mean.

Coefficients are the big numbers in front and are distributed to the whole molecule (which means you may have to multiply). Coefficients tell you how many molecules are present. 
     3He = He He He :)

Subscripts are the little lower numbers and they indicate the number of atoms and only apply to the atom it is to the right of. Subscripts tell you how many of each atom are present. Students wrote their name as a chemical compound and thought it looked pretty interesting. Some students have long formulas, other short.
We then led into counting atoms for real chemical formulas using subscripts and coefficients.
Be careful....
Here is the wonderful website these images came from. You may find it helpful.

Wednesday, September 12, 2012

Periodic Trends

Electro- negativity is how badly atoms want electrons. The most electronegative atoms are Fluorine, Chlorine, and Oxygen. Everyone wants to be a Noble Gas... and halogens are the closest so they are the most electronegative.

Ionization energy is how difficult it is to remove electrons. It is difficult to remove electrons from atoms that are electronegative.

Atomic radius increases as you move down the periodic table because atoms have more mass, but actually decreases from left to right because atoms are holding on to their electrons tighter (because they are more electronegative).

Shielding has to do with how protons are blocked by the electron shells - the more shells there are, the more blocking there is. So something in period 5 (with 5 shells) has more shielding than an element in period 2 with two electron shells. Sheilding is constant across the periodic table because the number of shells is constant.

Monday, September 10, 2012

Tiny tiny atoms

Atoms are really tiny and we need special microscopes to see them. Here is a neat website with pictures of atoms on a very small scale. This is an atom of Xenon on a Nickel surface.

It is no wonder that the model of the atom took so many turns and ideas to get it where it is today!

Thursday, September 6, 2012

Electronic Configuration

Battleship, a classic game by Milton Bradley, is a game easily adaptable to learning electronic configuration.

Electronic Configuration is an intense mathematical calculation proposed by Schrodinger & Heisenberg as a way to predict where to find an electron around the nucleus in the electron cloud model. 

There are four main parts of the periodic table known as orbitals. The S block, P block, D and F orbitals. Within each block, you just count over how many spaces it is. There are seven energy levels that are loosely based on the period that an element is (the D & F blocks are exceptions to energy levels). The D block is dumb and that's why it starts with one number lower. Really they just have less energy and have the same amount of energy as the S and P block in the 3rd period. The F block are failures and that's why they are 2 lower... or they have a lot less energy.

So to identify Hydrogen you would say 1s2 because it is in the first period or first energy level, in the s block, and the first member of the first block. Carbon is a 2P2 because it is in the 2nd period, in the P block, and the 2nd one over in the P block.

Students learned the pattern of electronic configuration and how to use it. Basically its like giving directions to an element on the PT using set landmarks. It is a bit confusing, but once you get the pattern, its not too bad.

Students practiced a bit and then they played Battleship to practice some more. The Periodic Table became the game board and students hid their ships on it, then guessed hits using the electronic configuration of the atoms. I think they really got the hang of it because I did not field many questions at that point.

Wednesday, September 5, 2012

Dudes & Models of the Atom

There are several "dudes," famous chemistry folks that students need to be familiar with. These dudes (Democritus, Dalton, JJ Thompson, Millikan, Rutherford, Bohr, Heisenberg, De Broglie, and Planck) all did experiments and came up with different and improved atom models. The current model is the elctron cloud or quantum mechanical model which was formulated by Heisenberg and De Broglie.

Heisenberg & De Broglie came up with the current electron cloud model, but we draw Bohr's planetary model the most often because it easier to count the electrons.

Electrons are tricky because they move constantly and at high speeds. Heisenberg's Uncertainty Principle states that you cannot know both the speed and location of an electron - you can only know one - because measuring either one, changes the other. DeBroglie's wave theory helps explain why electrons sometimes act like particles and sometimes are compared to waves.

For more information about the evolution of the atomic model, check out this link.

Tuesday, September 4, 2012

Atoms and the Periodic Table

Atoms, or elements, are the smallest unit of matter. They retain their identity in chemical reactions and are combined to form compounds and everything in the universe.

Atoms have some basic parts. Protons and Neutrons are found in the nucleus and make up the atomic mass. To find the number of neutrons, you subtract the atomic number (number of protons) from the atomic mass number (protons plus neutrons).

Electrons are so tiny that they do not influence the atomic mass. They are found orbiting the nucleus in shells or orbitals. Atoms are neutral so the number of protons equals the number of electrons.

We talked about the periodic table on Friday. Mendeleev deisgned the periodic table by looking at the properties of elements on cards and arranging them different ways until he got a system that worked. No one told him how to do it, he just did it until it worked. He even left spaces for elements that were discovered in his lifetime. (More info about Mendeleev) His periodic table was set up according to atomic mass number. The current table, altered slightly by Moseley, is organized by atomic number (number of protons).

Next we discussed regions of the periodic table, colored them, and labeled them. Periods are horizontal rows (periods go at the end of a sentence) and there are 7 periods. There are 18 groups or families (vertical columns) and a few of them have special names. This a pretty excellent diagram. This website gives a lot of helpful information.

We finished class by playing a quick game Guess Who.