The Periodic Table’s History:
We didn’t always have the periodic table!
by 1817, chemists had discovered 52
elements
by 1863 that number had risen to 62
Chemists needed a way to organize the
elements
The Periodic Table
Chemistry 11
William Odling: 1857
Found elements could be divided into 13
groups based on chemical and physical
properties
John Newlands (1863-1866):
Assigned hydrogen an arbitrary mass of 1
and ordered elements by their mass
Found every eighth element shared a
common set of properties (the law of
octaves)
Very elegant model, but did not allow for
prediction of new elements
Problem: every time new elements were
discovered, the table had to be rearranged
Dimitri Mendeleev (1869):
Russian chemist
Organized the elements according to their
masses and properties.
When he did this, he discovered that
certain properties recur PERIODICALLY
(like Newlands)
Some properties didn’t line up, so…
…he left gaps in his table for elements he
proposed had not yet been discovered
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Mendeleev’s Early Periodic Table
Henry Mosley (1887-1915):
developed the modern table in 1911 and
developed the Periodic Law
Periodic Law:
– The physical and chemical properties of the
elements are periodic functions of their atomic
numbers
Plain English:
– When elements are arranged in order of
increasing atomic number, similar properties
appear at regular intervals
What Stayed the Same?
Elements are still grouped by properties
Hydrogen is still the first element
What Changed?
Order is by increasing atomic number
Added a column of elements Mendeleev
didn’t know about
Filled in the gaps that Mendeleev predicted
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The Modern Periodic Table:
The table we see today wasn’t actually
“finished” until the early 1900’s.
Major Divisions of the Periodic Table
– The set of elements in a given row going
across the table.
– Strutt and Dorn added the Noble Gases in
1894
– The Lanthanides and Actinides were added in
the middle of the 1900’s
Period:
Still changes being made today, there are
always discoveries yet to be made!
Families of the Periodic Table:
Group or Family:
– The set of elements in a given column
going up and down the table.
Metals, Non-metals and Semi-metals
We can classify elements according
to their metallic character
The Properties of Metals:
–
–
–
–
–
Reflect light when polished (lustrous)
Are opaque
Are good conductors of electricity or heat
Generally, but not always, flexible when in thin sheets
Generally malleable (can be hammered into thin
sheets
– Generally ductile (can be stretched into wires)
– Usually solid at room temperatures (Hg is an
exception).
– React with acids
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The Properties of Non-Metals:
Are gasses, liquids, or brittle
solids at room temperature
Are poor heat and electricity
conductors
If solids, are dull to lustrous in
appearance and opaque to
translucent
Semi-metals / Semi-conductors:
Some elements share properties from both
metals and non-metals
Semiconductor:
– A non-metal having an electrical conductivity which
increases with temperature
A couple of important notes:
– Semiconductors were formally called “Metalloids”
– The important difference between metals and
semiconductors is that conductivity decreases with an
increase in temperature for metals.
Trends on the Periodic Table:
The elements change from
METALIC to NON-METALIC going
from LEFT to RIGHT across the
periodic table
The elements become MORE
METALIC (or better metals)
going DOWN a family on the
periodic table
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Alkaline-Earth Metals:
Alkali Metals:
– “group 1”
– soft, silver coloured metals
– React violently with water
– react with water in air
– form ions with charges of 1+
– “group 2”
– reactive metals
– form ions with
charges of 2+
– react with air
(oxidize) – ex. MgO
Myth busters Alkali Metals Video
Transition Metals:
– vary greatly in chemical
properties
– many have multiple
possible ion charges
– usually form colourful
compounds
Lanthanides / Actinides:
– Part of the Transition metals
– found at the bottom of the periodic
table
– varying chemical properties
– some elements are synthetic (not
naturally occurring)
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Halogens:
– “group 17”
– extremely reactive
– form ions with charges of 1– form acids with hydrogen (ex. HCl)
Noble Gases:
– “group 18”
– low reactivity (virtually unreactive)
Assignment:
– Periodic Table Worksheet
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