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 Dmetri 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.
1.
_______________________________________
2.
_______________________________________
3.
_______________________________________
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.