Ions
Chapter 7 Section 1
Valence Electrons
• Electrons in the highest occupied energy
level of an element
• The number of valence electrons largely
determines the chemical properties of an
element
• The group number of the representative
elements corresponds to the number of
valence electrons
Lewis Structure
• The valence electrons are the only electrons
used in chemical bonds.
• Therefore, only the valence electrons are
shown in an electron dot structure also called
a Lewis Structure
• Electron dot structures show the valence
electrons as dots
Lewis Structures
• N
• O
• Na
• B
The noble gases are unreactive in
chemical reactions because they
all have 8 valence electrons except
for He which has 2.
Octet Rule
• Gilbert Lewis explained why atoms form
certain kinds of ions and molecules
• He called his explanation the octet rule: In
forming compounds, atoms tend to achieve
the electron configuration of a noble gas
• An octet is a set of 8 electrons (noble gases
have 8 valence electrons)
Octet Rule
• Elements will behave differently based on the
type of element
• Metals will lose their valence electrons so that
their last energy level will have 8 valence
electrons (Sodium wants an electron
configuration like Ne)
• Nonmetals will gain electrons or share electrons
with another nonmetal to gain electrons so the
current energy level is an octet (Cl wants an
electron configuration like Ar)
7.1
Ions
• Atoms are electrically neutral because it has
equal numbers of protons and electrons
• An ion forms when an atom or groups of
atoms loses or gains electrons
Formation of Cations
• An atom’s loss of valence electrons produces a
cation or a positively charged ion
• Cations are produced by the loss of valence
electrons from a metal
• The name of the cation has the same name as
the element
• The sodium atom forms the sodium cation
7.1
Formation of Cations
• Sodium has 11 electrons, including 1 valence
electron
• The sodium Ion has an electron configuration
of Ne
• Sodium is now left with an octet
7.1
Formation of Cations
• The electron configuration of the sodium ion
is the same as that of a neon atom.
Loss of a valence electron
7.1
Formation of Cations
• Using electron dot structures, you can show
the ionization more simply.
7.1
Formation of Cations
• A magnesium atom attains the electron
configuration of neon by losing both valence
electrons. The loss of valence electrons
produces a magnesium cation with a charge of
2+.
7.1
Formation of Cations
• Cations of Group 1A elements always have a
charge of 1+.
• Cations of group 2A elements always have a
charge of 2+.
• Cations of group 3A elements always have a
charge of 3+
Transition Metal Cations
• Transition metals will not lose electrons to match
the noble gas before or after it.
• Silver would have to lose eleven to match krypton
and gain seven to match xenon
• Instead it will lose its 5s1 electron
• Pseudo noble gas configuration
• Ag 1s22s22p63s23p64s23d104p65s14d10
• Ag+ 1s22s22p63s23p64s23d104p64d10
7.1
Formation of Anions
• The gain of negatively charged electrons by
a neutral atom produces an anion.
• The name of an anion typically ends in -ide.
– Chlorine becomes Chloride
– Oxygen becomes Oxide
• Because they have almost full valence shells
nonmetal elements gain noble gas
configuration by gaining electrons
7.1
Formation of Anions
• A gain of one electron gives chlorine an octet
and converts a chlorine atom into a chloride
ion.
• It has the same electron configuration as the
noble gas argon.
7.1
Formation of Anions
• Both a chloride ion and the argon atom have an octet
of electrons in their highest occupied energy levels.
Gain of valence electrons
7.1
Formation of Anions
• In this equation, each dot in the electron dot
structure represents an electron in the
valence shell in the electron configuration
diagram.
Formation of Ions
• Ions produced when chlorine and other
halogens gain electrons are called halide ions
• All halide ions have a charge of 1-
7.1
Formation of Anions
• Oxygen is in Group 6A.
Gain of valence electrons
Formation of Anions
• Anions of Group 5A elements always have a
charge of 3-.
• Anions of group 6A elements always have a
charge of2-.
• Anions of group 7A elements always have a
charge of 1-