How does this thing work?

 Dmitri Mendeleev invented the PT (in 1869)  lived during the industrial revolution  found that the properties of elements repeat when arranged in order of increasing AM  “periodic” means “repeats at regular intervals”  from the P.T. one can predict the properties of unknown elements.

 Atomic number (#p + ) Mendeleev didn’t know about p+ but… The PT is arranged in order of increasing atomic number (#p+) and… The #p+ determines the element’s identity  Valence Electrons electrons in the highest occupied energy level play a key role in chemical reactions determines the chemical stability of an atom  an octet (8 valence e-) gives an atom chemical stability  Energy Levels The “rings” indicating how the “distance” and electron is from the nucleus e - can move from one energy level to the next by absorbing or releasing energy  ex: excited electrons absorb energy and move to higher energy levels

 The most obvious pattern is that the PT is arranged in rows & columns – this means something 7 Rows 18 Columns

 Periods – horizontal ( ↔ ) rows of elements  Period (row #) = # of energy levels Let’s note that on our PTs  All elements in Period 1 have 1 energy level  Row 4 all have 4 energy levels  The number of valence e- follows a pattern as you move across a period (exc. Transition metals)

 Groups/Families– vertical ( ↕ )columns of elements  elements in the same group/family have the same number of valence electrons  have similar chemical properties because they have the same number of valence electrons  Group # = # valence electrons (in A columns only)  All elements in Group1A have 1 valence e-  Row 7A all have 7 valence e-  B-columns (74%) & Rare Earth Metals (100%) the # of valence e- = 2 Let’s note that on our PTs

 Neils Bohr discovered the energy levels in the electron cloud Electrons could jump energy levels Looked like the solar system  So far the Periodic Table gives us the following information about an element: # of Protons from the atomic number # of total e- also from the atomic number (in neutral atom) # of energy levels from the Period (row #) # of valence e- from the Group (column #)  And the # of Neutrons can be calculated once we know the mass # # N = mass # - atomic #

1)Draw the Nucleus and enter: A. # P (= Atomic #) B. #N (= mass # - #P) 2)Determine the Total # e - (= #P) 3)Determine the # of energy levels and draw them (= Period or row#) 4)Enter the # of valence e- in the last energy level (= Group or column#) 5)Fill in the inside energy levels with electrons, starting at the first and working out, ending with the second to last energy level using up the remaining e -. RRemember: 1 st energy level holds up to 2 e - 2 nd energy level holds up to 8 e - 3 rd energy level holds up to 18 e- 4 th energy level holds up to 32 e- 19 p + K in group 1A = 1 valence e - 1e - 2e - 8e - K atomic # = n 0 K mass # = 41 so = 22 K has 19 p+ so… Total 19 e - K in P4 -1 e - 18 e - -2 e - 16 e - -8 e - 8 e - -8 e - 0e -

Diagram As-75 #1A#1A Enter the #p+ from the atomic number 42 n 0 33 p p + 42 n 0 #1B Subtract the #p + from the mass number to get the #n 0 and enter in the nucleus #1B #3 Draw the energy levels – P is in period 4 so draw 4 energy levels #4 Enter the valence e- P is in group 5A so enter 5 e- in the outer energy level #4 5 e - #3 #5 Enter the remaining e- from the inside, finish with 2 nd to last (subtract used e- from total to find) 2 e - 8 e - 18 e - #2 Write the total e- for a tally (As has 33 p + so it has 33 e - ) 33 e e- 18 e-

 the smallest piece of an element in which there is no charge  an atom with the same number of protons and electrons  # protons = # electrons 12 C 6 How many protons? How many neutrons? How many electrons? How many on the last (2 nd ) energy level? How many on the first energy level? 6p 6n 6 How many energy levels?2 4 2