ORGANIZING THE ELEMENTS
Section 16-1
Why is the PERIODIC Table important?
• Periodic – regular, repeating
pattern.
• Days of the year are organized
on a calendar.
• Periodic table is the most useful
tool to a chemist.
• It organizes lots of information
about all the known elements.
• You get to use it on most tests.
Pre-Periodic Table Chemistry …
• …was a mess!!!
• No organization of elements.
• Imagine going to a grocery store
with no organization!!
• Difficult to find information.
• Chemistry didn’t make sense.
• DISCOVER Activity on page 500
– Partner activity
– 4 sets of 10 numbers in various colors
Dmitri Mendeleev: 1869
Father of the Periodic Table
HOW HIS WORKED…
• Recognized a hidden pattern
• Put elements in rows by
increasing atomic mass.
(average mass of one atom of an element)
• Put elements in columns by
the way elements reacted or
the bonding power.
SOME PROBLEMS…
• He left blank spaces for
undiscovered elements and
predicted their properties.
(Turned out he was right!)
• He broke the pattern of
increasing atomic mass to
keep similar reacting elements
together.
Structure of an Atom
The Periodic Table and The ATOM
Electron Cloud or Electron Shell
•Outside the nucleus of an atom
•Most of the volume of an atom
•Negative electrons (1/2000 amu)
•Electrons move constantly and rapidly
around the nucleus
Nucleus
•Tiny core of an atom
•Most of the mass of an atom
•Positive protons (1 amu)
•Neutral neutrons (1 amu)
An Atom on the Periodic Table
26
Atomic Number P or E
•Element’s identity (social security number)
• Protons (also Electrons)
Atomic Symbol
•One or two letter symbol
•First letter is always capital
Iron
55.847
Atomic Name
•Origins in greek or latin root words
Atomic Mass (P + N)
•Protons (unique) + Neutrons (varies)
•Average mass of one atom
The Modern Periodic Table
• Mendeleev wasn’t too far off. The 3 missing
elements were discovered within 16 years.
• Now the 100+ elements are put in rows by
ATOMIC NUMBER!!
increasing
• The horizontal rows are called periods and are
labeled from 1 to 7.
• The vertical columns are called groups or
families are labeled from 1 to 18.
Exploring the Periodic Table
Valence Electrons – Why It Works!
VALENCE ELECTRONS
•Located in the outermost shell
•Involved in bonding
•HAPPY ATOM is when the
outermost shell is full
Load electrons from the inside
to the outside shell
1st shell – 2 electrons
2nd shell – 8 electrons
3rd shell – 8 electrons
Valence Electrons – Outermost Shell
The Modern Periodic Table