Download Chemical Bonds and Compounds

Bonding
The Statue of Liberty



What is the statue made of?
Why is it green if it is made of copper?
If pennies are made of copper, why are most of them
not green?
Bonds

Some matter around us is made of
uncombined elements (copper, sulfur,
oxygen, and other pure elements)
copper

sulfur
oxygen
Statue of Liberty is green because of a
compound formed when copper (Cu), sulfur
(S), and oxygen (O) combine chemically
(copper sulfate)
Bonds
The new compound formed now has
its own properties
 Compounds no longer have the
properties of the individual elements
that make the compound

Example
Sodium chloride or
salt (NaCl) has its
own properties……
….but as individual elements,
the properties are different….
Sodium (Na)
Chlorine (Cl)
Soft, silvery metal that reacts
violently with water
Greenish-yellow gas that is
poisonous
Formulas

Chemical Formula – Shows the elements
that a compound is composed of and the
exact number of atoms of each element
NaCl = 1 atom of sodium and 1 atom of
chlorine
H2O = 2 atoms of hydrogen and 1 atom of
oxygen subscript
*subscript – “written below”
*no subscript = 1 atom of an element
Practice
Familiar Name
Sand
Chemical Name
Silicon dioxide
Formula
SiO
Element ____________
silicon
Number of atoms ______
1
Element ____________
oxygen
Number of atoms ______
1
Water
Hydrogen oxide
H2O
hydrogen
Element ____________
Number of atoms ______
2
Element ____________
oxygen
Number of atoms ______
1
Atomic Stability
Compounds form because they are
more stable than the individual atoms
alone
 Noble gases are unusually stable and
very rarely form compounds…

…..why???
Atomic Stability
They have a filled and
stable outer energy
level (8 electrons)
1
This is known as the
octet rule
1
8
2
3
7
Argon
4
6
5
Valence electrons = 8
The Octet Rule

States that atoms of elements gain,
lose, or share electrons in order to
have 8 electrons in their outer shell

Goal is to achieve the stability of the
noble gases (which already have 8
electrons in their outer shell, with
exception of helium which has 2)
Atomic Stability
Chemically stable – When outer energy
level is complete
 Atom is stable when outer energy level
has 8 electrons (except H and He which
need two electrons to be stable)

Helium
Energy Levels
Is an atom of hydrogen stable?
No
Why not?
It only has 1 electron and
needs 1 more to fill its outer
energy level and become
stable
Hydrogen will be more stable when it forms a
compound with another element
Energy Levels
Is an atom of helium stable?
Yes
Why?
It has a full outer energy
level (stable)
- Helium rarely forms compounds because it already is
stable
- Elements in groups 13-17 are short of electrons in
their outer energy levels, therefore they easily form
compounds to have stable outer energy levels of 8
electrons (Lewis structures practice)
Ionic Bonding
Goal for bonding: To achieve stability!!
Sodium loses one electron and
chlorine gains one electron to
become stable
New inner energy level of sodium
becomes the stable outer energy
level by losing the single electron
it had in its outer energy level
Ions

Charged particle that has more or less
electrons than protons

Cation = Positive ion (loses electrons)

Anion = Negative ion (gains electrons)
Ions
- Sodium (Na) loses 1 electron
and becomes positively charged
with a charge of 1+ (cation)
- Chlorine (Cl) gains 1 electron and
becomes negatively charged with
a charge of 1- (anion)
Na
Cl
- Compound NaCl is stable and
has a neutral charge because
positive and negative charges of
the ions cancel each other
Ionic Bonds

What keeps the ions together?
– Force of attraction between the
opposite charges of the ions.

Does a compound have a charge?
– No because the charges of the ions
must cancel each other (compound is
neutral or have a zero charge)
Ionic Bonds

In an ionic bond, metals and
nonmetals bond

Elements that bond ionically are
usually across from each other in the
Periodic Table
http://www.wisconline.com/objects/index_tj.asp?
objID=GCH2204
Ionic Compounds
Covalent
Compounds
Contain positive and negative ions (Na+Cl-)
Exist as neutral
molecules (C6H12O2)
Solids suchs as table salt (NaCl(s))
Solids, liquids,or gases
(C6H12O6(s), H2O(l),
CO2(g))
High melting and boiling points
Lower melting and
boiling points (i.e.,
often exist as a liquid
or gas at room
temperature)
Strong force of attraction between particles
Relatively weak force
of attraction between
molecules
Separate into charged particles in water to give a
solution that conducts electricity
Remain as same
molecule in water and
will not conduct
electricity