mendeleev (1).ppt excellent to use as a teaching aid

very good resource

1. Everything in BLUEneeds to go in your notes!

2. Discovering the Elements
By the year 1869, sixty
three elements had
been discovered.
A Russian scientist
named Dmitri
Mendeleev discovered
that the elements
followed certain
patterns.

3. Mendeleev’s Role
Mendeleev noticed that some elements
shared physical and chemical
properties.
Example: fluorine and chlorine are both
gases that irritate your lungs.
Example: copper and silver are both metals
that tarnish when exposed to air.

4. Patterns
Mendeleev tried to find patterns in the
elements using
Melting point
Density
Color
Atomic mass
Chemical bonds

5. Patterns
He noticed that if he put the elements in
order of increasing atomic mass,
patterns appeared.
He also noticed that the properties of the
elements repeated.
He put these elements in order by
atomic mass, but also grouped them
according to properties.

6. Each color is a different “group” on the Periodic Table.
The elements in these groups share common properties
and will react in similar ways.

7. Groups on the Periodic
Table
Elements in the same group have
similar chemical and physical
properties!!
(Mendeleev did that on purpose.)
Why??
•They have the same number of valence
electrons.
•They will form the same kinds of ions.

8. How Did He Do It?
For example:
After fluorine, the next heaviest known
element was sodium. Sodium reacted with
water the same way that lithium did. So he
placed those elements into the same group.

9. Predicting New Elements
When Mendeleev began placing the
elements in order based on common
properties and atomic masses, he noticed
that there were a few empty spaces.
Mendeleev predicted that the blank spaces
would be filled by elements that had not yet
been discovered.
He could even predict the properties of the
unknown elements!

11. Finding the Missing
Elements
Within 16 years of Mendeleev’s Periodic
Table, the missing three elements were
discovered.
They were called scandium, gallium,
and germanium.
Their properties were very close to what
he had predicted.

12. The Modern Periodic Table
The Periodic Table that we use today is
very similar to Mendeleev’s first version.
New elements have been added as they
have been discovered.
Look in your pink sheets to see the
modern Periodic Table of Elements.

14. Atomic Number
The only major change occurred in
1913, when a scientist named Henry
Moseley discovered how to measure an
atom’s atomic number.
The Periodic Table was rearranged in
order of atomic number instead of
atomic mass.

15. Review
1. What was the name of the scientist who
first developed the Periodic Table?
2. How many known elements were there at
that time?
3. How did he set up his Periodic Table?
4. What was he able to predict about
unknown elements using his Periodic
Table?
5. How has the Periodic Table changed since
then?

16. Answers
1. Dmitri Mendeleev
2. 63 elements
3. He put the elements in order of
increasing atomic mass.
4. He was able to predict the existence of
unknown elements and the chemical
properties of those unknown elements.
5. The elements are now in order by
atomic number and there are now more
than 100 known elements.