Post on 07-Apr-2019
The Periodic Table
Part One
The Basics
What does periodic mean?
Having or marked by repeated cycles
What things in our everyday life do we notice as cyclic or periodic?
What are some of the patterns you notice on the periodic table?
There are many important people who played a key role in organizing the elements in such an intricate fashion…
Antoine Lavoisier (1790’s)
Compiled a list of
known elements at
the time (23)
What elements do you
think were included
here?
Gold, silver, oxygen,
carbon
The 1800’s brought
about big changes…
What are some big things that may have affected the knowledge of chemistry?
Electricity
Development of the spectrometer
Industrial revolution (mid-1800’s) Lead to many chemical industries…soaps, dyes,
fertilizers
But not all good things came from the revolution Chemical pollution now an issue
70 known elements by the 1870
In addition to new elements…
New scientific data that provided insight into the properties of compounds and elements
A tool for organization became necessary
Big step: 1860 Scientists agreed on a method for accurately
determining the atomic masses of the elements (finally!)
What would be the problem with not having a universal way to measure the mass of elements?
Now the search for relationships between mass and elements was on…
John Newlands (1864)
English chemist
Proposed organization scheme
Noticed elements were arranged by increasing atomic mass
Also, their properties repeated every eigth element 1st and 8th
2nd and 9th
What do were call this repeating pattern?
Newlands called it: The Law of Octaves Octave is a group of musical notes
that repeats every eighth tone
Newlands organized
the first 14 known
elements
Elements with similar
properties were in the
same row
How does this
compare with our
current periodic table
Newlands organized the first 14 known elements
Elements with similar properties were in the same row
How does this compare with our current periodic table
The Law of octaves was not readily
accepted b/c it did not work with all
elements
Newlands law was also criticized b/c the
use of the word octave was considered
very “unscientific”
The important thing was that Newland
recognized that properties of elements
were repeated
Lothar Meyer (1869)
German chemist
Demonstrated connection between atomic mass and elemental properties
Did not receive as much credit as Dmitri Mendeleev because he did not publish his organization scheme first
Dmitri Mendeleev (1869) Russian chemist
demonstrated connection between atomic mass and elemental properties
Noticed (like Newlands) that when elements were put in order of atomic mass there was a periodic repetition of their elemental properties
Arranged elements in order of increasing atomic mass into columns with similar properties
This was the first periodic table
Mendeleev’s table was widely accepted
because it predicted the existence and
properties of undiscovered elements
Blank spaces on the table
Predicted properties of yet to be
discovered elements such as scandium,
gallium, and germanium
But there were problems…
New elements discovered and atomic
masses were more accurately determined
Elements in Mendeleev’s table not in
correct order
Arranging elements by mass now put
groups of elements together with different
properties
Henry Moseley (1913)
English Chemist
Figured out the problem with Medeleev’s Table
What did Moseley Discover before? Atoms of each element
contain unique number of protons in their nuclei
He arranged elements in order of increasing atomic number and not increasing atomic mass
Problem Solved!
Moseley’s arrangement solved the problems with Mendeleev’s table
His arrangement resulted in clear periodic patterns of properties
Lead to Periodic Law:
Statement that there is a periodic repetition of chemical and physical properties of the elements when they are arranged in increasing atomic number
Modern Periodic Table
What’s in the box?
What does the 1 stand for? Atomic Number
This tells us what about an atom of H?
# of protons
What does the 1.007947 stand for? Atomic Mass
This tells us what about an atom of H?
Mass in nucleus (# of protons and neutrons)
On the modern periodic table, how are
elements arranged?
In order of increasing atomic number, left to
right
What do we call the columns (up and
down) on the periodic table?
GROUPS (or families)
What do we call the rows (left and right) on
the periodic table?
PERIODS
What does periodic mean?
Having or being marked by repeated cycles
What element does period 1 begin with?
H
How many periods are there on the table?
7
Periods
Groups Two different number systems for
groups. In the first numbering system, groups are number 1-8 and each number is followed by either an A or B
The groups labeled A are the main groups (1A thru 8A) Representative elements
This is because they possess a wide range of chemical and physical properties
The groups designated with a B (1B thru 8B) are found in the center Transition Elements
A more recent numbering system has been devised numbering 1-18