History of the Periodic Table
•
•
•
•
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
1). Dobereiner’s triads (1829)
• 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
Limitations of Dobereiner’s triads
It’s triads applicable for only few elements. It was not applicable
for all the 30+ known elements.
•
•
•
•
•
•
•
•
2). Newland’s law of octaves (1864)
mid 1800’s
56 @ 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
During this time, 56 elements were discovered. He
arranged these known elements in the increasing order of
their ATOMIC MASS.
Statement of Newland’s law:
If elements are arranged in the increasing order of
their atomic mass, then the property of every eight
elements (starting from the first element) repeats.
Limitations of Newlands law of octaves
•Similarity in properties as per the law was seen up to calcium
only.
•He stated that only 56 elements exist in nature. But later on,
he was proved wrong and many more elements were
discovered.
•Dissimilar elements were placed in the same slot.
•Similar elements were placed in different slots.
3). Mendeleev law (1869)
• Mendeleev 1860’s @ 63 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
Mendeleev law:
The properties of elements are the periodic functions of
theirs atomic masses
This table is known as the Mendeleev periodic table of elements.
• 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
Mendeleev law:
The properties of elements are the periodic functions
of theirs atomic masses
• 1st Periodic Law: properties of the elements are
a periodic function of their increasing atomic
masses
• Mosley explained exceptions with discovery of
Atomic Number
• Modern Periodic Law: properties of the
elements are a periodic function of their
increasing atomic number
4). Modern Periodic Law (1913)
• The properties of the elements are the Periodic
function of their ATOMIC NUMBERS.
Modern Periodic Law was given by Henry Moseley in 1913.
•Mandeleev law says that the properties of elements are the
functions of their atomic mass. While,
•Modern periodic law says that the properties of elements are
the Periodic function of their atomic number.
• 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
1st Period
2nd Period
3rd Period
4th Period
5th Period
6th Period
7th Period
Periods in Periodic table:
The periods are the horizontal rows.
There are 7 horizontal rows.
1.
2.
3.
4.
5.
Vertical columns are called GROUPS,1- 18
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
MOSELY MODREN LONG PERIODIC TABLE
https://periodictableguide.com/periodic-table-ofelements/#google_vignette
• P.T. is actually a repetitive pattern of ECN's
• Still does go by increasing atomic number
• Why?
• 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
•
•
•
•
•
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
•
•
•
•
•
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
• 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)
• Other important feature of P.T.
• Staircase
• Separates metals on left, from non-metals
on right
• Elements on staircase are referred to as
metalloids
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
• https://periodictableguide.com/all-periodictrends-in-periodic-table/
•
•
•
•
•
•
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
Metalloids
• Share some of but not all of the
characteristics of both metals and nonmetals