1. Arrange the following atoms in order of increasing ionization energy: oxygen, lithium, strontium, chlorine, tellurium and magnesium. Explain your order.
2. Why do you think that we say the properties of the periodic table are "periodic"?
3. Lock at your model and select an element that seems to have an unusual value for one of these properties. Some of the elements show exceptions to the trends. Explain why this happens by writing the electron configuration for this element and looking for a definite change from the element before it.