

Organization of electrons
in energy levels
Each energy level can hold
a certain number of
electrons
◦
◦
◦
◦

1st level=2 electrons
2nd level=8 electrons
3rd level=18 electrons
4th level=32 electrons
Maximum number of
valence electrons=8
 Highest
occupied energy level of
an atom is filled with electrons
◦ 8 electrons in the highest energy
level signifies the atom is stable
Noble gases are
stable with 8
valence electrons
 Usually do not
react with other
elements

 Atoms
will gain or lose electrons
to become stable
◦ All elements want to become stable
like the noble gases
◦ A chemical bond forms between
atoms to make a compound
 2 types: Ionic and Covalent

Have one, two, or three more electrons than
they need in order to be stable
◦ Determined by number of valence electrons

In order to become stable, they can:
◦ Lose electrons, or
◦ Combine electrons with another metal

Have less than the number of electrons they
need in order to be stable
◦ Determined by the number of valence electrons

In order to become stable, they can:
◦ Gain electrons, or
◦ Share electrons with another nonmetal
Model of an atom in which each dot
represents a valence electron.
 The symbol in the center represents
the nucleus and all the other electrons
in the atom.
 Used when illustrating how atoms gain
or lose electrons to achieve stability

The transfer of electrons from one
atom to another to achieve a stable
electron configuration
 Forms between a metal and a
nonmetal



Metal will give away 1, 2, or 3 electrons to the
nonmetal
Bond will form between the atoms and create a
compound

When an atom gains or loses an
electron, the number of protons is no
longer equal to the number of
electrons.
◦ The atom is no longer neutral
◦ An Ion has formed
 atom that has a net positive or negative
electric charge
 represented by a plus or minus sign

Two types of ions:
1. Cation
 ion with a positive charge, atom
lost/donated electron(s)
 Metals
2. Anion
 ion with a negative charge, atom
gained electron(s)
 Nonmetals
A
sodium ion has 11 protons and 10
electrons.
The sodium ion has a charge of 1+.
• The symbol for the ion is written Na1+,
or Na+ for short.
•
The
ion that forms when a chlorine
atom gains an electron has 17 protons
and 18 electrons.
• This ion has a charge of 1–.
• The symbol for the ion is written Cl1–
, or Cl– for short.


The amount
of energy
used to
remove an
electron
The lower the
ionization
energy, the
easier it is to
remove an
electron from
an atom.


Compounds that contain ionic bonds
Represented by chemical formulas
◦ Notation that shows what elements a compound
contains and the ratio of the atoms or ions of these
elements in the compound
◦ EX: NaCl
 From this you can tell there is 1 sodium ion and 1
chlorine ion
 Ratio 1:1
◦ EX: MgCl2
 The 2 is called a subscript, used to show how many
atoms of that element are in a compound
 1 magnesium ion and 2 chlorine ions
 Ratio 1:2

Example:
◦ When sodium reacts with chlorine, an electron is
transferred from each sodium atom to a chlorine
atom.
◦ Each atom ends up with a more stable electron
arrangement than it had before the transfer.

Example:
◦ Sodium transfers 1 valence electron to
chlorine
◦ This gives chlorine 8 valence electrons

Example:
◦ When the transfer occurs an ionic bond
forms between the two atoms
◦ Sodium becomes positive because it lost
an electron, so it is the cation
◦ Chlorine becomes negative because it
gained an electron, so it is the anion
 Ionic
compound would be:
NaCl

Example:
◦ Magnesium has 2 extra electrons…it will give these
to chlorine so that chlorine can be stable
◦ An ionic bond forms
◦ Mg is cation with +2 charge because it gave away 2
electrons
◦ Cl is anion each with a -1 charge because each one
received 1 electron

Ionic compound would be:
MgCl2

Examples:
◦ Na2S
◦ BeF
◦ K3P
◦ Li2O
◦ RbF
◦ AlCl3
 All
form crystals
 Tend to have high melting and
boiling points
 Are very hard and very brittle
 Conduct electricity when they
dissolve in water
 Solids
whose particles are
arranged in a lattice structure

Ions are arranged in an
orderly, threedimensional structure.
• Each ion is attracted to
all the neighboring
ions with an opposite
charge.
• This set of attractions
keeps the ions in fixed
positions in a rigid
framework, or lattice.