The Periodic TableHow does this thing work?

The Periodic Table History 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.

One of Mendeleev’s Tables

Some terms before we start

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

Periodic Table Organization The most obvious pattern is that the

PT is arranged in rows & columns – this means something

7 Rows

18 Columns

The Rows on the PT are Periods 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)

The Columns on the PT are Groups 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

Wow – there’s a lot of information here!

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 #

Let’s try a Bohr model of Potassium (K-41)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-.

Remember: • 1st energy level holds up to 2 e-

• 2nd energy level holds up to 8 e-

• 3rd energy level holds up to 18 e-• 4th energy level holds up to 32 e-

19 p+

K in group 1A = 1 valence e-

1e-

2e-

8e-

8e-

K atomic # = 19

22 n0

K mass # = 41 so 41-19 = 22K 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 n0 33 p+

-33 p+

42 n0 #1B Subtract the #p+ from the mass number to get the #n0 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 2nd 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-

-15 e-18 e-

This has been an example of a Bohr model using a NEUTRAL

atom

the smallest piece of an element in which there is no charge

an atom with the same number of protons and electrons

# protons = # electrons12

C

6

How many protons?How many neutrons?

How many electrons?

How many on the last (2nd ) energy level?

How many on the first energy level?

6p6n

6

How many energy levels? 24 2