Compounds

1
Compounds and Chemical Bonding
2
Neutral atoms contain an equal number of protons
which have a positive charge
and electrons which have a negative charge.
In addition, most atoms contain one or more
neutral particles called neutrons.
3
Atoms are naturally balanced. The number of
protons is equal to the number of electrons.
However, most atoms are not chemically stable.
The outer energy level is not completely filled.
Atoms would rather be stable than balanced, so
they share or steal electrons and become
compounds.
4
Why do atoms combine?
The positive charge in the proton of one atom is
attracted to the negative charge of the electrons
in another atom. This attraction is the glue
that holds atoms together.
This glue is a chemical bond.The bonded atoms are
now a compound.
5
What are compounds?

• Think about a compound word such as hotdog.

• The words hot and dog have defined meanings or
  properties.

• The combined word has a new meaning.

6
What are compounds?

• Compounds are chemically bonded atoms.

• The properties of compounds are different than
  the properties of uncombined atoms.

• For example, sodium (Na) is a soft, shiny metal
  that reacts violently with water.

• Chlorine (Cl) is a toxic, yellowish gas.

• When combined, NaCl is table salt.

7
What properties are used to position elements on
the periodic table?
1 1A
188A
2 2A
133A
144A
155A
166A
177A
1
2
3 3B
4 4B
5 5B
6 6B
7 7B
111B
122B
3
4
5
6
7
of protons atomic number
of energy levels period
of valence electrons group or family
8
This is a Bohr model of a calcium atom.
How many electrons are present in the last energy
level?
Only the outer shell, or valence electrons are
involved in bonding. In general, atoms form
compounds in order to have 8 outer shell
electrons. With 8 outer shell electrons, atoms
are chemically stable.
9
This is a Bohr model of a neon atom.
How many electrons are present in the last energy
level?
Stable atoms in group 8, like neon, have 8
valence electrons. Other atoms form compounds in
order to have 8 electrons. This is the octet
rule.




To draw a dot diagram, place one dot for each
electron present in the last energy level. Draw
single dots on each side before pairing them.
10
Valence Electrons
11
Valence Electrons

• the number of electrons in the outer energy level

• corresponds to the group number

1 1A
188A
2 2A
133A
144A
155A
166A
177A
3 3B
4 4B
5 5B
6 6B
7 7B
111B
122B
12

• Atoms are stable when there are 8 valence
  electrons.

• Atoms with only one or seven valence electrons
  are especially reactive.

• these electrons are available to be shared or
  stolen by other atoms

1 1A
188A
2 2A
133A
144A
155A
166A
177A
3 3B
4 4B
5 5B
6 6B
7 7B
111B
122B
13
Oxidation numbers

• Atoms are electrically neutral because they have
  the same number of protons and electrons.

• Opposites attract! What type of bond have the
  ions formed?

• Just as when people on a diet feel positive when
  they lose weight, ions that result from losing
  electrons have a positive charge. Those that gain
  electrons have a negative charge.

• However, atoms would rather be stable than
  neutral. Atoms in groups 1, 2, and 13 give up
  electrons to become more stable. They become ions!

• Atoms in groups 15, 16, and 17 gain electrons to
  become more stable. They also become ions!

-

14
Types of Compounds
15
Ionic Compounds

• Ionic bonds occur between metals and non-metals
  on the periodic table.

• In general, the metallic elements in groups 1, 2,
  and 13 have positive valence numbers. This means
  they have electrons to give up.

• The non-metallic elements in groups 15, 16, and
  17 have negative valence numbers. This means
  they are anxious to steal electrons.

1
1 1A
188A
133A
2 2A
144A
155A
166A
177A
3
2
-1
-2
-3
3 3B
4 4B
5 5B
6 6B
7 7B
111B
122B
16
Covalent Compounds

• Most atoms choose to share electrons when they
  bond.

• Covalent bonds occur between 2 nonmetals.

• These bonds can happen between 2 atoms of the
  same element resulting in diatomic atoms.

17
Chemical Formulas
18
Chemical Formulas

• describe compounds

• list which atoms are present in the compound

• express the ratio of each atom present

Consider the formula for water
H2O

• The small 2 is a subscript. It indicates that
  for each molecule of water, 2 atoms of hydrogen
  are present for each atom of oxygen.

19
Consider the formula for potassium nitrate
KNO3
How many atoms of potassium are present?
How many atoms of oxygen are present?
How many atoms of nitrogen are present?
Consider the formula for aspirin
6C9H8O4

• The six is a coefficient. It tells us how many
  molecules of the whole compound are present.
  Multiply the coefficient and subscript to
  determine the number of atoms of each element
  present in the formula.

How many atoms of carbon are present?
How many atoms of hydrogen are present?
How many atoms of oxygen are present?
20
Bibliography
Bonding. (1999). Chemzone Ithaca City School
District. Available. Online http//207.10.90.10
5/chemzone/lessons.htm
Hsu, Tom. (2002). Integrated Physics and
Chemistry. Peabody, MA Cambridge Physics Outlet.
American Chemical Society. (2002). Chemistry in
the Community Fourth Edition. New York W.H.
Freeman and Company.
Ions. (1997-2002). Chem4Kids Andrew Rader
Studios. Available. Onlinehttp//www.chem4kids.
com/files/atom_ions.html
Modified from 2004 Plano ISD