Intro to the periodic table
Unit 5
Mendeleev and the first periodic table
Middle of the 19th century,
Dmitri Mendeleev organized the known
elements their atomic masses
Mendeleev’s first sketch of the periodic
table and the first published periodic table
(1869)
 Did you notice there are some blanks on Mendeleev’s
first periodic table???
He was so confident that his organization of elements
showed repeating properties that
He was able to predict undiscovered elements!!
Two problems with the first P table
1. Why could most of the elements be
arranged in order of increasing mass but a
few could not?
2. What was the reason for chemical
periodicity (why did properties repeat)?
The Answer
40 years later
 Henry Moseley organized the periodic table by
atomic number (number of protons)
Elements fit into groups better
The Modern Periodic table
Is organized in order of increasing atomic
number
Modern Periodic law
The discovery and use of atomic
numbers to organize the p. table led
to the
Periodic law: Properties of elements
repeat periodically when elements are
arranged by atomic number
Groups And periods
-groups/families: vertical columns, have similar
properties
-periods: horizontal rows
Representative Elements
All of the elements found in
group 1,2, 13-18 are called the
representative elements.
Why?
Represent all 3 types of elements,
metals, nonmetals and metalloids
Representative Elements
Types of Elements
 Metals
•A metal is an element that is a good conductor
•TO THE LEFT OF STARICASE
• Some properties of metals
•most are solids at room temperature
•Malleable
•ductile
•conduct electricity and heat well
Metals: gold, copper, aluminum
Types of Elements
Nonmetals
• A nonmetal is an element that is a poor conductor
• TO RIGHT OF STAIRCASE
• Some properties of nonmetals
• many are gases
• solids are brittle
• poor conductors of heat and electricity
Nonmetals:
carbon, sulfur, phosphorous, iodine
Metalloids
Metalloids
•A metalloid is an element that has characteristics
of both metals and nonmetals
• Properties of metalloids
• all metalloids are solids at room
temperature
• semiconductors of electricity
Metalloids
 Check your understanding: Would most elements on
the periodic table be metals, nonmetals, or metalloids?
The s block
 Group 1 A:, alkali metals (not H)
MOST reactive metals
React with water
Group 2 A, alkaline earth metals
harder and denser that group 1
not as reactive as group 1, but still very
reactive
The d block
Groups 3-12: Transition metals
Typically less reactive than groups 1-2 so can
be found as free elements in nature
aka: Group B
The halogens
Group 17
The most reactive nonmetals
The noble gases
Group 18: All gases
Inert (meaning unreactive; don’t form
compounds because they already have all
the electrons they need)
The bottom block
Every wonder why there are two rows of
elements below the periodic table?
Inner Transition Metals, they would mess
up trends if they were actually in the table
so we pull them out!
Lanthanide series (top row)
Actinide series (bottom row)
 The lanthanides
Between group 3 and 4 in the 6th period
Similar in reactivity to alkaline earth metals
Fun Fact: Lutetium has almost no applications.
As a result it used to be the most expensive
element in the world. These days it is easily
available as a side product of other lanthanide
production and its price has fallen.
 The actinides
Between group 3 and 4 in the 7th period
All radioactive; all above Np are man made
Fun Fact: A radioactive button like this is inside
most smoke detectors. A trace of americium
creates charged particles that betray the
smoke. Americium is thus the only man-made
element available in grocery stores.