PreAP Chemistry Chapter 6 – Periodicity
______- properties of the elements are a periodic function of their atomic numbers.
The earliest and most successful arrangement of the elements was by Dmitri Mendeleev in the 1870s. He arranged the elements known at that time by their ______and ______properties into groups. His arrangements of the elements left some gaps, which he claimed were elements not yet discovered. With his table he predicted the characteristics of these missing elements, and was correct.
During the 1910s, Henry Moseley used x-ray spectra to determine the ______(number of protons) for elements and proved that each element had a different amount of protons. Moseley rearranged the elements based on atomic number, as it is arranged today, and found gaps which he also claimed were undiscovered elements. Some of these elements were found quickly, while others were not found until after his death due to their highly radioactive (unstable) nature.
There are three key items in understanding and explaining all the trends (and exceptions) on the periodic table.
1. ______
2. ______
3. ______
1. Effectice Nuclear Charge – pull of the ______in the nucleus on the valence (outer) energy level electrons. The greater the ______, the greater the number of protons, and the greater the ______. Effective nuclear charge has the greatest effect moving from ______to ______across a period (it increases).
Which element has more effective nuclear charge, P or S? ______
Which element has more effective nuclear charge, S or Se? ______
2. Energy levels – the principal quantum level of the electrons, sometimes called ______. As elements increase in atomic number they also increase in the number of ______. These electrons occupy higher and higher energy levels. Higher numbered energy levels are ______away from the nucleus. Energy levels have the greatest effect moving from ______to ______within a group (it increases).
Which element has more energy levels, S or Se? ______
Which element has more energy levels, P or S? ______
3. Coulomb’s Law state that the force of attraction between things is directly proportional to the ______of the charge and inversely proportional to the square of the ______between them. What two things are attracted to each other in an atom? ______Which one can move? ______
Which situation would show the stronger force of attraction? Explain ______
Which situation would show the stronger force of attraction? Explain ______
For the following trends, you must know the general trends (memorize), but using the three key items you must be able to explain the trend as well (understand).
1. ______- size of the atom
a. ______from top to bottom within a group
Why does it increase from top to bottom? ______
b. ______from left to right within a period
Why does it decrease from left to right? ______
2. ______- energy required to ______an electron from a gaseous atom
a. ______bottom to top
Why is it easier to remove electrons from atoms at the bottom of the P.T.? ______
______
b. ______left to right
Why is it easier to remove electrons from atoms at the left of the P.T.? ______
______
c. This is sometimes called ______, as metals tend to lose electrons easily.
Which element would exhibit the most metallic character? ______
3. ______- energy released when an electron is added to a gaseous atom
a. ______bottom to top
Why is more energy released when electrons are added to atoms at the top of the P.T.? ______
b. ______left to right
Why is more energy released when electrons are added to atoms at the right of the P.T.? ______
c. This is sometimes called ______, as nommetals tend to gain electrons easily.
Which element would exhibit the most nonmetallic character? ______
4. ______- measure of an atom’s pull on another atom’s electrons
a. ______bottom to top
Why are atoms at the top of the P.T. able to pull stronger on a different atom’s electrons? ______
______
b. ______left to right
Why are atoms at the right of the P.T. able to pull stronger on a different atom’s electrons? ______
______
5. ______- charged atoms
a. ______- ______ion formed from an atom losing an electron. The ionic radius is always ______than the original atom. Why? ______
b. ______- ______ion formed from an atom gaining an electron. The ionic raidus is always ______than the original atom. Why? ______
Let’s summarize the trends. Remember you must know the trends (memorize), but you also need to be able to explain why the trend exists.