Valence Electrons are the electrons in the
outermost shell of an atom.
They are important in telling how the atom will
react with certain chemicals.
Like other electrons, the valence electrons can
absorb and release energy.
Chemical bonds are the forces that hold particles of
matter together.
Some elements do not usually form bonds.
These are the elements in Group 18. The noble gases.
They each have a complete outer energy level and are
considered stable because of their electron configuration.
Ions
Many atoms gain or lose electrons and end up with the same
number of outer
electrons as a noble gas.
When a neutral atom loses or gains electrons, it becomes a charged particle
A charged particle is called an ion.
In an ion the number of protons and the number of electrons are not equal.
If there are more protons than electrons the ion will have a positive charge. IF there
are more electrons the ion will have a negative charge.
Usually metals lose electrons and non metals gain electrons.
When a neutral sodium atom loses one electron, it becomes a
positive sodium ion.
11 protons
10 electrons
The sodium ion
has a charge of 1+.
Na1+
Ionic bonding is perhaps the easiest of the three bond types to comprehend because
it ties in with the idea that opposites attract. Specifically, opposite electric charges
attract one another.
Remember that metallic atoms tend to lose electrons. When they do so, they become
positively charged ions which are called cations.
Nonmetallic atoms tend to gain electrons to become negatively charged ions which
are called anions.
These oppositely charged cations and anions are attracted to one another because of
their opposite charges. That attraction is called an ionic bond. We often refer to the
charge on the ion as the oxidation state of that element.
Potassium Bromide
Potassium is a metal, silvery-white in color. It easily decomposes when exposed to
water, and it also catches fire easily during this reaction.
Bromide, a non-metal, is a liquid with reddish-brown color. As one of the examples of
ionic bonds, the chemical bonding that occurs between bromide and potassium produces
potassium bromide.
KBr has uses in veterinary medicine as a treatment for animals with epilepsy. It is also
utilized in photographic plates and paper manufacturing.
1. How is an ion different from an atom?
2. What is an ionic bond?
3. What are some properties of ionic bonds?
4. Write the formulas for each:
magnesium chloride calcium oxide
lithium bromide carbon monoxide
zinc chloride potassium iodide
1. An ion is a charged particle, and atom is neutral.
2. An ionic bond is a force of attraction between two
oppositely charged particles.
3. The bonds in an ionic bond are very strong. Ionic
compounds are very stable, have high melting points, high
boiling points, Usually they are brittle, and do not conduct
electricity as solids, but will conduct when melted or
dissolved in water.
4. Write the formulas for each:
magnesium chloride calcium oxide
lithium bromide carbon monoxide
zinc chloride potassium iodide
MgCl
LiBr CO
ZnCl2 KI
CaO
Consider the elements lithium, sodium potassium and
rubidium in Group 1. They all have one valance electron and
all form an ion with a charge of 1+. Rubidium gives up its
electron to form a positive ion much more easily than does
any of the others. Potassium gives up its one electron easily
than do the rest, and sodium gives up its electron more easily
than lithium. Can you explain this?
Think about it and write your answer in your notebook......
Covalent bonding is what we call the strong attraction that holds together the atoms of
nonmetallic elements. It is found in elements and in compounds. It is also found
within the polyatomic ions. Essentially it is found in any material in which nonmetallic
atoms are bonded together.
In covalent bonding, both atoms are trying to
attract electrons--the same electrons. Thus, the
electrons are shared tightly between the atoms.
The force of attraction that each atom exerts on
the shared electrons is what holds the two atoms
together.
The shared electrons of a covalent bond can be represented using Lewis
diagrams. The bond can be emphasized by using a line to "hold the atoms
together." The electron dots that are not involved in the bond are
sometimes shown and sometimes not shown.
What is the difference between the chemical bond that
forms NaCl and Cl2?
Metallic Bonds
Most metals have one, two, or
three electrons in their outer
energy level. During many
chemical reactions, metal
atoms lose their outer
electrons to other atoms,
usually nonmetals.
The larger metals lose their outer electrons the most easily,
because these electrons are farther away from the pull of
the positively charged nucleus. A metal atom becomes
stable, or nonreactive, when it has lost its outer electrons.
What kind of bonding is this?
The outer electrons in a metal atom are far from the
nucleus and are held in place loosely.
In a metallic solid the atoms are so
close together that their outer
energy levels overlap. Because of
these conditions, the outer
electrons are able to move from
one atom to another.
In a metallic solid, the outer
electrons are thought of as
belonging to the whole
structure rather than to
single atoms. This
structure is called a
network.
A network of metal atoms
Blue are metal atoms
Red are electrons
The metallic network is made up of positively
charged metal ions with electrons all around
them. The force of attraction that holds the
network together is called a metallic bond.
The network is an arrangement of positive ions in a
sea of electrons.
This freely moving sea of electrons explains why
metals conduct electricity.
Electrons that enter one end of
a wire flow through the wire and
out the other end.
The metallic bond also explains
why metals are malleable and
ductile.
Because there are no individual bonds, the ions and
electrons can be moved into new positions without cracking
or
breaking the metal object.
The sea of electrons and ions
is rearranged each time a metal
is forced into a new shape.
Metallic Bonds
Ionic Bonds
metal to non metal atoms
electrons are lost and gained
metal to metal atoms
sea of electrons,
electrons belong to
the entire network
Covalent Bonds
nonmetal to nonmetal
electrons are shared