10-26-09

Regarding the dart lab: It's due Thursday. Use a line graph for the graphs. Clarity is important; neatness isn't. If you had hits outside of the circle, add a row for >10cm, calculate the area of the sheet of paper (remember to convert inches to centimeters), and add your data. Hits are infinitely significant for calculations. The figure on the sheet is not the one from you book. Use Fig. 11 on page 107.

Atomic Radii

• The boundaries of an atom are fuzzy, and an atom's radius can vary under different conditions.
• To compare different atomic radii, they must be measured under specific conditions.
• Atomic radius may be defined as one-half the distance between the nuclei of identical atoms that are bonded together.
• Atoms tend to be smaller the farther to the right they are found across a period.
• The trend to smaller atoms across a period is caused by the increasing positive charge of the nucleus, which attracts electrons toward the nucleus.
• Atoms tend to be larger the farther down in a group they are found.
• The trend to larger atoms down a group is caused by the increasing size of the electron cloud around an atom as the number of electron sublevels increases.

Sample Problem E

Of the elements Mg, Cl, Na, and P, which has the largest atomic radius? Highlight for answer. Na. All of these elements are in the same period, and Na is right-most.

Ionization Energy

• An ion is an atom of group of bonded atoms that has a positive or negative charge.
• Na, for example, easily loses an electron to form Na+.
• Any process that results in the formation of an ion is referred to as ionization.
• The energy required to remove one electron from a neutral atom of an element is the ionization energy, IE (or first ionization energy, IE1).
• In general, ionization energies of the main-group elements increase across each period.
• This increase is caused by increasing nuclear charge.
• A higher level charge more strongly attracts electrons in the same energy level.
• Among the main-group elements, ionization energies generally decrease down the group.
• Electrons removed from atoms of each succeeding element in a group are in higher energy levels, farther from the nucleus.
• The electrons are removed more easily.

P.S. Since I'm such a nice guy, I'll give somebody a chance to volunteer to do the blog tomorrow. If nobody does, I'm going to pick somebody using a random number generator, so no whining if luck doesn't favor you.