EX: Ca =    40 amu
        Ba = 137 amu
average = 88.5 amu Sr = 87.6 amu (very close!)
 

b. 1863 - John Newlands (English Chemist) arranged elements in order of increasing atomic mass; he noted similar properties in every 8th element; he grouped them into seven groups of seven each and called it the "Law of Octaves"
 

c. 1869 - Dmitri Mendeleev (Russian Chemist) noted that properties of elements are periodic functions of their atomic masses; Na and Li have similar physical and chemical properties so they belong in the same family; he left holes in his table where properties did not fit and predicted the properties of the missing elements; he suggested how and where to look for them; first person to try and put the elements into a table
 

d. 1913 - Henry Moseley said properties are periodic functions of their atomic numbers; called this the "Periodic Law"; this is our modern periodic table

e.  1944 -- Glenn Seaborg - worked on the Manhattan Project  (atomic bomb) and realized that the elements Lanthanum and Tantalum belonged deparate from the rest of the table;  He moved them into the "f" block and predicted the presence of other elements, which were then discovered.
 

1. vertical columns; also called groups
2. similar properties
3. same # valence electrons; outer electron configuration is the same

b. names

1. alkali - group 1
2. alkaline earth - group 2
3. transition metals - groups 3-12
4. boron - group 13
5. carbon - group 14
6. nitrogen - group 15
7. chalcogen (oxygen) - group 16
8. halogens - group 17
9. noble gases - group 18
10. rare earth metals - "f" block

*NOTE: groups 1,2,13-18 are representative elements or main group elements
 

1. horizontal rows; also called series
2. properties repeat periodically
3. each element increases by one valence electron as you proceed across the row
4. elements change from metals to metalloids to nonmetals across a period

b. names

each row is numbered 1-7
 

1. shiny, ductile, good conductors, malleable, hard
2. found to left of staircase
3. easily lose electrons to become positive ions

b. metalloids

1. properties of both metals and nonmetals
2. found along staircase except for Al
3. sometimes gain electrons; sometimes lose electrons

c. nonmetals

1. brittle, solids or gases, dull, poor conductors/ good insulators
2. found to right of staircase
3. gain electrons to become negative ions

d. noble gases

1. filled outer energy level
2. very stable
3. do not gain or lose electrons so unreactive
 
 

1. atoms get larger as you move down a column because more energy levels are filled
2. atoms get larger as you move left because electrons aren't as attracted to nucleus

b. ionic radius

1. positive ions are larger than their neutral atoms because electrons are not pulled in as much
2. negative ions are smaller than their neutral ions because electrons are pulled in tighter

c. ionization energy - energy required to remove an electron

1. harder to remove electrons as you move right because the sublevels are more filled and they would rather accept electrons not lose them
2. He is hardest element to take electrons away from because they are close to the nucleus
3. easier to remove as you go down a column because electrons "feel" nuclear charge less

d. electronegativity - tendency for an atom to attract electrons to itself in a chemical bond

1. Noble gases have no electronegativity because they don't form compounds and are already full
2. F is most electronegative because it already has seven valence electrons and only needs one more to complete its shell; also the electrons are very near the nucleus
3. electronegativity decreases down a group because the electrons "feel" the nuclear charge less

e. electron affinity - desire that an element has for another electron

1. noble gases have no affinity for electrons because they are already full
2. F has greatest desire for an electron because it only needs one electron to complete its valence shell and because it is close to the nucleus