Atomic properties and periodic trends...

For Students:

The picture shown above gives and more or less accurate depiction of the atomic size trends going across the periodic table.  As you can see the largest atoms are in the bottom left of the periodic table.  Francium must be huge!  It is one of the biggest atoms, but not really huge, remember that atoms are approximately 10^-11 m in diameter.

Next we will look at electron affinity which is the energy required to add an electron to an atom in the gas phase.  In other words, how much that atom resists aquiring a new electron.

As you can see atoms in the top right corner really don't want any more electrons.  Helium is not going to be taking on any more electrons any time soon.  And this make sense because helium's shell is already full and it would have to make a new shell to hold any more electrons.  This would take a huge amount of energy to do!
Finally we will look at ionization energy which is the amount of energy required to remove an electron from a particular atom in its gas state.

It is essentially the same as the electron affinity but you have to remember that for electron affinity the values are getting more and more negative as you move up and right in the periodic table.  The energy required to add an electron is negative if something really resists it.  The ionization energy goes up when you move up and right in the periodic table in a positive way.  This means that it would require more and more energy to remove an electron  as you move up and right.

For Parents:
There will be a quiz tomorrow instead of Friday and on Friday we will be having our 2nd test of the semester.  Please make sure your child understand what is going on and please have them ask questions if they don't understand something on the study quide.  Hopefully things go well Friday!  Thanks!