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: 1869Father 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

Nucleus • Tiny core of an atom • Most of the mass of an atom• Positive protons (1 amu)• Neutral neutrons (1 amu)

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

26

FeIron

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An Atom on the Periodic Table

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

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

increasing ATOMIC NUMBER!!• 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!

P+ N

1st shell – 2 electrons2nd shell – 8 electrons3rd shell – 8 electrons

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

Valence Electrons – Outermost Shell

P+ N

The Modern Periodic Table