The periodic table organizes the elements based on their atomic structure and properties. Dmitri Mendeleev created one of the earliest periodic tables in the 1860s that arranged the then-known elements in order of increasing atomic mass, with similar properties recurring periodically. This allowed him to predict properties of undiscovered elements. Niels Bohr later explained that atomic number, not mass, determines an element's position. Modern periodic tables are arranged by atomic number and illustrate how each element's outer electron configuration determines its chemical properties and placement in groups.

1. History of the Periodic Table

2. • Fast facts
• 91 naturally occurring elements
• Oxygen is most abundant element
• Tie together properties that make metals,
metals and non-metals, nonmetals
• Early 1800’s scientists started to note
relationships between certain elements and
their atomic masses
• Classification of elements began using these
similarities

3. • Dobereiner @40 known elements
• First scientist to observe an important trend
• Noticed certain groups of three elements
had similar physical and chemical
properties but different masses
• Called them TRIADS
• Ex. Li,Na,K Cl,Br,I Cu,Ag,Au Be,Mg,Ca

4. • Newland
• mid 1800’s
• 45 @ known elements
• Noted connection of properties and mass were a
repeating pattern in order of increasing mass
• Every 8th element had similar
properties(Dobereiner’s Triads)
• Didn’t know about Noble gases
• Called it Law of Octaves
• Problems occurred as more elements were
discovered and did not fit pattern

5. • Mendeleev 1860’s @ 60+ known elements
• Father of Periodic Table (P.T.)
• Developed table that showed relationship between
properties of elements and atomic masses
• Remember: the only thing known about atoms is?
• Dalton’s Theories
• No e- or p+
• Carefully planned and in great detail
• Avoided earlier mistakes of forcing elements to fit
into 8 pattern like Newland

6. • Proposed properties were a function of increasing
atomic mass
• Believed similar properties occurred after periods
that could vary in length by specific patterns
• Left blank spaces on table were an element did not
fit ( did not force elements in) properties
• Predicted that spaces were undiscovered elements
• Predicted masses and properties of unknowns
• Elements discovered were very close to
predictions
• Elements properties repeated in an orderly way

7. • Not all elements fit pattern
• Ex. Te-I and Co-Ni
• Mendeleev switched elements around even
though masses were not in pattern
• Believed properties were more important
factor to consider
• Predicted a new theory or discovery would
explain this
• 1st Periodic Law: properties of the elements
are a periodic function of their increasing
atomic masses

8. • Mosley explained exceptions with
discovery of Atomic Number
• Modern Periodic Law: properties of the
elements are a periodic function of their
increasing atomic number

9. • Using a P.T.
• Elements arranged in horizontal rows in
order of increasing atomic number
• 5 things found on every P.T.
• 1. Symbol of element
• 2. Atomic number of element
• 3. Atomic mass of element
• 4. 7 periods
• 5. 18 groups and 2 series

10. • Period
• Horizontal row, 7 total
• Begins on left side, 1st element always has a
single e- in valence shell
• Each Period ends on right with a Noble Gas,
an element with 8e- in the valence shell
• Period shows the HIGHEST energy level
currently being filled

11. • Vertical columns are called GROUPS,1- 18
• Also referred to as Families
• Share similar chemical and physical
properties
• Number of valence e- in a Group are all the
same
• Same ending ECN
• Only difference is the number of energy
levels

12. • Family names
• Group 1 Alkali metals
• Group2 Alkaline earth metals
• Group 17 Halogens
• Group 18 Noble gases

13. • Look at Periods
• 1
• 2
• 3
• 4
• 5
• 6
• 7

14. • Transitional elements
• d-block
• Have incomplete d sublevels
• e- are filling in d sublevel
• All transitional elements as a group share
similar chem & phys properties

15. • Look at Groups
• Group 1
• Group 2
• Groups 3-11
• Group12
• Group 13
• Group 14
• Group 15
• Group16
• Group 17
• Group 18

16. • 2 Series
• Lanthanoid
• Actinoid

17. • P.T. is actually a repetitive pattern of ECN's
• Still does go by increasing atomic number
• Why?

18. • An atoms chemical properties are based on
its ending ECN
• Can use the table to read an elements ECN
• Group 1 all end in s1
• Group 2 all end in s2
• Called the s-block
• Transition elements all end in a d (1-10)
• Called d-block

19. • Groups 13-18 all end in p (1-6)
• Called p-block
• Lathanoids and Actinoids all end in f (1-14)
• Some ECN’s are not what expect however
• Due to the added stability by the
rearrangement of the e- in the outer
sublevels

20. • Some ECN’s are modified
• Due to stability factors
• Ex. Cr 1s2 2s2 2p6 3s2 3p6 4s2 3d4
• Changes to 1s2 2s2 2p6 3s2 3p6 4s1 3d5
• Half-filled or completely filled sublevels are
more stable than incompletely filled
sublevels
• Due to e- spin and distribution
• Only occurs in incomplete d and f filling
sublevels

21. • Octet Rule
• When there are 8e- in the outer energy level
of an atom s2p6, the atom is rendered
unreactive
• Atoms react with each other because the
resulting system is more stable after the
reaction than before
• ECN is one of the most important factors
leading to atom stability
• Atoms want to achieve s2p6 (Noble Gas
configuration)

22. • Other important feature of P.T.
• Staircase
• Separates metals on left, from non-metals
on right
• Elements on staircase are referred to as
metalloids

23. Metals
• Shiny (luster)
• Hard
• Conduct electricity and heat well
• Malleable
• Ductile
• Generally have three or fewer e- in their valance
levels
• Tend to lose e- in the bonding process

24. Non-metals
• Brittle
• No luster
• Do not conduct heat and electricity
• Generally have 5 or more e- in their valence
shell
• Tend to gain or share e- in the bonding
process

25. Metalloids
• Share some of but not all of the
characteristics of both metals and non-
metals