Atoms and the Periodic
Table


Atoms are the basic building blocks of all
matter.
Atoms are made up of:
1.
2.
3.
Protons—Positively charged particles; found in
the nucleus
Neutrons—Particles that have no charge; found
in the nucleus
Electrons—Negatively charged particles; found
outside the nucleus
Nucleus containing two
protons and two neutrons
+
+
-
1st energy level containing two
electrons

The number of protons and electrons will
be the same in a neutral atom.


Elements are made up of atoms.
Elements: substances that cannot be broken
down into simpler chemical substances

examples: Gold, Iron, and Silver
Atoms of:
ELEMENT
Pure Gold
18-Karat Gold
14-Karat Gold

The Periodic Table is a table with all of the
elements found on earth.
How to Read the Periodic Table



Chemical Symbol:
the letters
Atomic Number:
found above the
chemical symbol
Atomic Mass: found
below the chemical
symbol



Atomic Number = # of protons (= # of electrons)
# of neutrons = atomic mass – atomic #
Isotope: Atoms of the same element that have
different numbers of neutrons
two isotopes of Sodium
Ions: atoms that gain or lose electrons;
have a positive charge (more protonscalled a cation) or a negative charge
(more electrons-called a anion)
 Valence Electron Rule (Outermost)
 1-3 electrons- lose- positive -cation
 4- covalent bond (covalent bond-share a
pair)
 5-7 electrons – gain- negative - anion
 8 –Inert because the atom is full ( Noble
gases

Electron Shell Diagram and
Electron Dot Formula
1st electron shell can hold 2 electrons
 2nd electron shell can hold 8 electrons
 3rd electron shell can hold 8 electrons

1st
2nd
Nucleus
3rd

Electron shell diagram: shows the
arrangement of all the electrons
surrounding the nucleus of an atom
The first 2 electrons go
in the 1st energy level.
The other 4
electrons go in
the 2nd energy
level.
6P
6N
If we have 6 protons
in the nucleus, we
need to have 6
electrons in the
energy levels around
the nucleus.

Electron dot formula: shows the number
of electrons in the outermost electron shell
First, you write
the symbol for
the element.
C
Next, you draw a
dot for each
electron in the
outermost energy
level. You can put
dots on four sides
of the symbol—
top, bottom, left,
and right. Put the
dots in pairs.