Download Chapter 7 Section 1

Chapter 7 Section 1
Ions
Valence Electrons




The electrons in the highest occupied
energy level.
The group number of a representative
element tells you the number of
valence electrons.
Helium is the one exception
Valence electrons are the electrons
used in almost all chemical bonds.
Dot Structures



Electron dot structures show valence
electrons as dots.
The number of dots for an element
will be the same as its group number.
Ex.= H· ·Mg·
Octet Rule



Atoms try to get a set of eight
electrons when they form compounds.
Atoms of groups 1,2,3 will try to lose
valence electrons to leave a complete
octet in the next highest energy level.
Atoms of groups 5,6,7 will try to gain
electrons to fill their highest energy
level with an octet.
Cations




The loss of valence electrons by an
atom produces cations (+).
For metals, the name of the cation is
the same as the element’s name.
Na·  Na+ + e –
A sodium atom will ionize into a
sodium(+1) ion and an electron(-1)




Group 1 elements form cations with
+1 charges because they have one
valence electron to lose.
Group 2= 2+
Group 3= 3+
Transition metals (group B) do not
always follow the octet rule.
Anions




An atom can gain an electron to form
an anion (negative charge)
The name of the anion is the name of
the element with the ending –ide
Chlorine- Chloride, Oxygen- oxide
Groups 5,6,7 gain electrons to form
anions.






Chlorine has seven valence electrons.
Add one electron to form an ion.
Cl atom + e-  Cl- ion
The ions produced when halogens
(group 7) gain electrons are called
halide ions (F-, Cl-, Br-, I-.
Oxygen has six valence electrons, add
two electrons to form an oxide ion.
O atom + 2e-  O2- ion
Chapter 7 Section 2
Ionic Bonds and Ionic Compounds
Ionic Compounds





Compounds composed of cations and
anions.
Ionic compounds are neutral
Ionic compounds are held together by
ionic bonds.
Sodium cholride is an example.
Na + Cl  Na+ + Cl-
Formulas



A chemical formula shows the kinds
and numbers of atoms in one unit of a
substance.
Example- Sodium chloride would have
a chemical formula of NaCl.
This shows the ratio of Sodium to
Chloride is 1:1, this ratio is called a
formula unit.
Ionic Compounds




Ionic compounds are usually solid
crystals at room temperature.
In Sodium chloride, each Na+ ion is
surrounded by six Cl- ions. Each Clion is surrounded by six Na+ ions.
This results in high stability and very
high melting points.
NaCl melts at about 800 Celsius.
Coordination number



The coordination number of an ion is
the number of ions of opposite charge
that surround an ion in a crystal.
Ex- NaCl would be 6. Each Na+ ion is
surrounded by 6 Cl- ions.
Ionic compounds can conduct an
electric current when melted or
dissolved in water.
Chapter 7 Section 3
Bonding in metals
Metallic bonds



Metals are made up of closely packed
cations rather than neutral atoms.
The valence electrons of metals can
flow freely from one area to another.
Metallic bonds consist of the attraction
of the valence electrons to the positive
charge of the metal cation.
metals




Metals are good conductors of
electrical current because electrons
can flow freely.
Metals form crystalline structures.
Metals are ductile and malleable
Ductile means able to be drawn into
wires. Malleable means they can be
hammered or forced into shapes.
Alloys




Alloys are mixtures composed of two or
more elements, with at least one being a
metal.
Most of the metals we see and use are
alloys.
The properties of alloys are often superior
to those of the elements making them up.
Bronze and steel are two common alloys.
Alloys



Sterling silver is 92.5% silver and
7.5% copper. It is harder and more
durable than pure silver.
Bronze is 7 parts copper and 1 part
tin. It is harder than copper and more
easily cast.
Steel is the most important alloy.