Transcript the periodic table

THE PERIODIC TABLE
Dmitri Mendeleev
• A Russian scientist who began to classify the
60 known elements of his time
• Worked with the indivisible model of an
atom
• Atomic masses were known in comparison to
hydrogen, which was set as "1"
“I began to look about and write down the elements with
their atomic weights and typical properties, analogous
elements and like atomic weights on separate cards, and
this soon convinced me that the properties of elements are
in periodic dependence upon their atomic weights.”
--Mendeleev, Principles of Chemistry, 1905, Vol. II
• Mendeleev discovered that the properties
of the elements repeated at regular
intervals when the elements are arranged
in order of increasing atomic mass
periodicity: the occurrence of similar
physical and chemical properties of
elements at regular intervals
• Mendeleev stated that elements arranged
in order of increasing atomic mass show a
periodic repetition of properties
• He left blank spaces for where he
predicted (based on properties) an element
should be
– He predicted (accurately!) the properties of
yet-undiscovered elements!!!
Observed properties of Eka-Silicon and
observed properties of Germanium:
Property
Observed Predicted Observed Found for
for Si
for Eka- for Sn
Ge
Silicon
Atomic Mass
28
72
118
73
Melting Point
(oC)
1410
High
232
947
Density
(g/cm3)
2.33
5.5
7.28
5.35
Boiling point
of chloride
(oC)
57.6
100
114
84
In the meantime…
• Thomson and Rutherford discovered
the proton and the electron
• Chadwick, in Rutherford’s lab made
another discovery: the neutron!
• SO… an atom is made of
– Positive protons, mass of 1, symbol p+
– Uncharged neutrons, mass of 1, symbol no
– Negative electrons, mass of 0, symbol e-
mass number
(atomic mass)
x
A
z
atomic number
atomic symbol
Atomic mass = number of protons +
neutrons
Atomic number = number of protons
So what's the number of electrons?
• Moseley working together with
Rutherford discovered that the
element's properties could be even
better predicted using the number of
charges the atom had: atomic number
• elements were re-arranged by atomic number (as
in the modern Periodic Table)
• elements arranged in order of increasing atomic
number show a periodic repetition of properties
• - each column of the periodic table (called a group)
has similar properties (periodic trends)
The Periodic Law
- chemical and physical properties of element vary in
a periodic way with their atomic number
Hands-On: elemental samples (Helen)
The modern Periodic Table
• Scientists divide elements into 3 categories
1. Metals
•
•
•
•
Alkali metals
Alkaline earth metals
Transition elements
Inner transition elements
2. Non-metals
• Halogens
• Noble gases
3. Metalloids
• elements are arranged in increasing
order of atomic number, as you go from
left to right across the table.
– The vertical columns are called "groups“ or
“families”.
– The horizontal rows are called "periods".
representative elements
transition elements
inner transition elements
alkali metals
noble gases
alkaline earth metals
transition metals
lanthanoids
actinoids
halogens
Metals
• left side and centre of periodic table
• Solid at room T (except mercury, Hg)
• Silver (except Cu and Au)
• Shiny, conduct electricity and
heat, malleable and ductile
malleable:
capable of being shaped, the degree
to which it can be shaped by pounding
with a hammer
ductile:
physical property of being capable of
sustaining large deformations without
breaking (for example being drawn
into a wire)
Non-metals
•
•
•
•
•
Right side of periodic table
Found in all three states
Variety of colours
Poor conductors of heat/electricity
Usually brittle (having little elasticity: easily
cracked or fractured or snapped )
Metalloids
• Along zig-zag line dividing
metals and non-metals
• Metalloids are: Boron, Silicon,
Germanium, Arsenic, Antimony,
Tellurium, Polonium
• Have some metallic and nonmetallic properties
• Ex. Si - silicon: shiny,
nonmalleable, a semi-conductor