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How Big Are Atoms?
Five-hundred-million gold atoms lined up side-byside would form a line as long as a $10 bill.
Look around your home and you’ll be amazed at the variety of chemicals
in your cupboards and on your shelves.
In the bathroom, you’ll find water, soap, shampoo, and toothpaste - all
chemicals.
In the basement or garage, you may find cleaning products, such as ammonia
and bleach, and perhaps painting and gardening products.
In your kitchen, you’ll likely find table salt, baking soda, and baking powder.
Each of these compounds has a chemical name and a chemical formula.
The formula identifies which elements, and how much of each, are in the
compound.
So, for example, table salt’s chemical name is sodium chloride and its formula
is NaCl.
Baking soda’s chemical name is sodium bicarbonate and its chemical
formula is Na(HCO3).
NAMING CHEMICAL COMPOUNDS
Until the 18th century, no standardized system existed for naming
chemicals. This created confusion because the names for chemical
compounds varied from country to country and scientist to scientist.
For example, hydrochloric acid and muriatic acid refer to the same
thing.
If you didn’t know that, you might think they were two different
chemicals.
Today, some compounds are better known by their common name.
Bleach, for instance, is almost always used instead of the chemical
name aqueous sodium hypochlorite.
In 1787, a French chemist named Guyton de Morveau created a naming
system, or nomenclature, for compounds.
He decided to use the chemical name for each element in the compound,
always putting the metal element first. For example, zinc and oxygen combine
to form zinc oxide.
Since 1920, the International Union of Pure and Applied Chemistry
(IUPAC) has been the body responsible for agreeing on the appropriate name
for every chemical compound discovered.
INTERPRETING CHEMICAL NAMES AND FORMULAS FROM
COMPOUNDS
If you know only the formula of a chemical compound, you can
determine its chemical name.
If you know only its name, you can determine its formula.
Table salt’s chemical name, sodium chloride, indicates that the compound is
made of one atom of sodium and one atom of chlorine
Its chemical formula, NaCl, indicates this too.
One sodium atom
combines with one chlorine atom
to form the compound sodium chloride,
which we call table salt
Now look at the formula for the compound water: H2O.
Notice that next to the H is a small 2 as a subscript.
(“Sub” means below.)
The 2 indicates that there are two atoms of hydrogen to go with every atom of
oxygen in water.
Subscript numbers in a chemical formula indicate the number of atoms of the
elements that must combine to form the compound.
No subscript number indicates that only one atom of that element is needed.
In water, two hydrogen atoms join with each oxygen atom.
Compound
sodium
chloride
water
Chemical
Formula
Elements
NaCl
• sodium
•chlorine
H20
• hydrogen
• oxygen
No. of Atoms
of Each
1
1
2
1
Total No.
of
Atoms
2
3
INDICATING THE PHYSICAL STATE OF A COMPOUND
Another common notation added to chemical compounds indicates the
state of the chemical at room temperature.
After the chemical formula, a subscript s for solid, l for liquid, or g for gas
is shown in parentheses.
For example, sodium chloride is written as NaCl(s),
water is written as H2O(l),
and natural gas (methane) is written as CH4(g).
For aqueous solutions (substances dissolved in water), a subscript aq
in parentheses is added to the formula.
So, if sodium chloride was dissolved in water,
the resulting aqueous solution would be written as NaCl(aq).
Glucose
C6H12O6 (s)
The chemical formula for glucose tells us that each molecule is
made of 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen
atoms and the (s) indicates it is a solid. 24 atoms in all.
Common Name: Peroxide
Scientific name :
Hydrogen peroxide
Chemical Formula:
H2O2 (aq)
Number of Elements:
2 – Hydrogen, Oxygen
Number of Atoms of each element:
Hydrogen- 2 Oxygen- 2
2 elements 4 atoms
Common Name:
Sugar
Scientific name :
sucrose
Chemical Formula:
C12H22O11 (s)
Number of Elements:
3 – Carbon, Hydrogen, Oxygen
Number of Atoms of each element:
Carbon-12 Hydrogen- 22 Oxygen- 11
3 elements 45 atoms
Common Name:
Baking soda
Scientific name :
sodium hydrogen carbonate
Chemical Formula:
NaH(CO3) (s)
Number of Elements:
4 – Sodium, Hydrogen, Carbon, Oxygen
Number of Atoms of each element:
Sodium - 1 Hydrogen - 1 Carbon -1 Oxygen - 3
4 elements 6 atoms
Common Name:
Rubbing alcohol
Scientific name :
2-propanol
Chemical Formula:
CH3CH(OH)CH3 (l)
Number of Elements:
3 – Carbon, Hydrogen, Oxygen
Number of Atoms of each element:
Carbon-3 Hydrogen- 8 Oxygen- 1
3 elements 12 atoms
Common Name:
Aspartame
Scientific name :
aspartyl-phenylalanine methyl ester
Chemical Formula:
C14H18N2O5 (s)
Number of Elements:
4 – Carbon, Hydrogen, Nitrogen, Oxygen
Number of Atoms of each element:
Carbon-14 Hydrogen- 18 Nitrogen- 2 Oxygen- 5
4 elements 39 atoms
Common Name:
Milk of Magnesia
Scientific name :
Magnesium Hydroxide
Chemical Formula:
Mg(OH) 2(s)
Number of
Elements:
3 - Magnesium , Oxygen, Hydrogen
Number of Atoms of each element:
1 - Mg , 2- Oxygen, 2- Hydrogen
3 elements 5 atoms
Common Name:
Citric acid
Scientific name :
2-hydroxy-1,2,3- propanetricarboxylic acid
Chemical Formula:
C3H4(OH)(COOH)3 (s)
Number of
Elements:
3 - Carbon , Hydrogen, Oxygen,
Number of Atoms of each element:
Carbon - 6, Oxygen - 7, Hydrogen - 8
3 elements 21 atoms
Sodium, shown in (a), is a metal.
Sodium combines with chlorine gas in a violent reaction (b).
The product is table salt, NaCl(s) (c).
2Na
Na + +
ClCl2
2
→→
NaCl
2 NaCl
Sodium chloride is called an ionic compound.
Ionic compounds are pure substances formed as a result of the attraction
between particles of opposite charges, called ions.
Table salt is formed from positively charged sodium ions and negatively
charged chloride ions.
Other properties of ionic compounds include: their high melting point, good
electrical conductivity, and distinct crystal shape.
All ionic compounds are solids at room temperature.
In fact, table salt will not melt until it is heated to 801°C.
When an ionic compound is melted or dissolved in water, it will conduct
electricity.
This property of ionic compounds led to the study of electrochemical cells (cells
that either convert chemical energy into electrical energy or electrical energy
into chemical energy). And that work in turn eventually led to the invention of
batteries.
“Ion” Origin
The word “ion” comes from a Greek word meaning “to go” or “wander.”
When the ionic compound is dissolved in water, the metal and nonmetal
form an aqueous solution of ions.
An ion is an atom or a group of atoms that has become electrically charged
through the loss or gain of electrons.
The following table shows some examples of ion charges for various
elements.
Sodium - Na
Sodium – Ion charge 1 +
Sodium will lose 1 electron
Sodium has 1 valence electron
Think of it as being able to fill in 1 hole.
Chlorine Cl
Chlorine – Ion charge 1 –
Chlorine gain 1 electrons
Chlorine has 7 valence electrons
Think of it as having 1 hole.
The crystals in this table salt are held together by ionic bonds.
Ion Charges
To indicate ions in written notation, a plus sign (+) or a minus sign (-) is
placed to the upper right of the element symbol.
This is a superscript position (super - means “above”).
For example, a sodium ion is written as Na + and a chlorine ion as Cl -.
Naming Ionic Compounds
1. The chemical name of the metal or positive ion goes first,
followed by the name of the non-metal or negative ion.
2. The name of the non-metal negative ion changes its
ending to ide.
Hydrogen – Hydride Nitrogen - Nitride Phosphorus – Phosphide
Oxygen – Oxide Sulfur – Sulfide Selenium – Selenide Fluorine – Fluoride
Chlorine – Chloride Bromine - Bromide Iodine - Iodide
Lithium
Fluoride
Li F
Lithium 1+ has 1 extra valence electron – can fill one hole
Fluorine 1- missing 1 valence electron – has one hole
2. Lithium + Oxygen
Lithium
Oxide
Li 2 O
Lithium 1+ has 1 extra valence electron – can fill one hole
Oxygen 2 - missing 2 valence electrons – has two holes
Lithium 1+ can fill one hole – you need 2 Li atoms to fill 2 holes
2. Lithium + Nitrogen
Lithium
Nitride
Li 3 N
Lithium 1+ has 1 extra valence electron – can fill one hole
Nitrogen 3 - missing 3 valence electrons – has three holes
Lithium 1+ can fill one hole – you need 3 Li atoms to fill 3 holes
4
Sodium Chloride
NaCl
5
Sodium Sulfide
Na2S
6
Sodium Nitride
Na3N
7
Sodium Phosphide
Na3P
8
Potassium Bromide
KBr
9
Potassium Sulfide
K2S
10
Potassium Nitride
K3N
11
Beryllium Iodide
Bel2
12
Beryllium Oxide
BeO
13
Beryllium Nitride
Be3N2
14
Calcium Fluoride
CaF2
15
Calcium Oxide
CaO
16
Calcium Phosphide
Ca3P2
17
Magnesium Iodide
MgI2
18
Magnesium Sulfide
MgS
19
Magnesium Nitride
Mg3N2
20
Magnesium Chloride
MgCl2
Metals that have more than 1 ionic charge
Some elements with more than one ion charge:
Titanium 3+ or 4+
Iron
3+ or 2+
Nickel
2+ or 3+
Copper
1+ or 2+
Lead
2+ or 4+
Gold
1+ or 3+
Mercury 1+ or 2+
Use Roman Numerals to indicate the charge
used – I, II, III, IV, V, VI, VII, VIII
Titanium 3+ or 4+ , Iron 3+ or 2+ , Nickel 2+ or 3+ , Copper 1+ or 2+ , Lead 2+ or 4+
Gold 1+ or 3+ , Mercury 1+ or 2+
Roman Numerals to indicate the charge used –(1) I, (2)II, (3)III, (4)IV, (5)V, (6)VI, (7)VII, (8)VIII 1.Titanium III Fluoride
F 1Ti
One atom of titanium will fill 3 holes
One atom of fluorine will has 1 hole to fill
3+
Titanium IV Fluoride
Ti
F
One atom of titanium will fill 4 holes
One atom of fluorine will has 1 hole to fill
4+
1-
2.Titanium IV Oxide
Ti
O
One atom of titanium will fill 4 holes
One atom of oxygen will has 2 holes to fill
4+
2-
Titanium III Oxide
Ti 3+
O 2One atom of titanium will fill 3 holes
One atom of oxygen will has 2 holes to fill
Ti F3
Ti F4
Ti O2
Ti 3 + O 2
Ti O
-
3. Titanium III Nitride
.
Titanium IV Nitride
Ti N
Ti3N4
4. Iron III Chloride
FeCl3
Iron II Chloride
FeCl2
5. Iron III Sulfide
Fe2S3
Iron II Sulfide
FeS
6. Copper I Oxide
Cu2O
Copper II Oxide
CuO
8. Lead II Fluoride
Pb F2
Lead IV Oxide
PbO2
9. Gold I Oxide
Gold III Nitride
10. Mercury I Oxide
Mercury II Nitride
Au2O
AuN
Hg2O
Hg3N2
Polyatomic Ions
Some ions can also form when certain atoms of elements
combine.
These ions are called polyatomic ions (poly - means “many”).
Polyatomic ions are a group of atoms acting as one.
The formula is written in brackets.
The name will not end in ide.
Ammonium (NH4)1+
Bicarbonate (HCO3)1- Hydroxide (OH)1- Nitrate (NO3)1Nitrite (NO2)1Carbonate (CO3)2- Sulfate (SO4)2- Sulfite (SO3)2Phosphate (PO4)3-
Polyatomic Ions
Cations (+1 Charge)
Ammonium (NH4)+
Polyatomic Ions
Anions (-1 Charge)
Bicarbonate (HCO3)-
Polyatomic Ions
Anions (-1 Charge)
Hydroxide (OH)-
Polyatomic Ions
Anions (-1 Charge)
Nitrate (NO3)-
Nitrite (NO2)-
Polyatomic Ions
Carbonate (CO3)2-
Anions (-2 Charge)
Polyatomic Ions
Sulfate (SO4)2-
Sulfite (SO3)2-
Anions (-2 Charge)
Polyatomic Ions
Phosphate (PO4)3-
Anions (-3 Charge)
1. Ammonium + Fluorine
Ammonium Fluoride
(NH4)F
2. Ammonium + Oxygen
Ammonium Oxide
(NH4)2O
3. Ammonium + Nitrogen
Ammonium Nitride
(NH4)3N
4. Sodium + Hydroxide
Sodium Hydroxide
Na(OH)
5. Magnesium + Hydroxide
Magnesium Hydroxide
Mg(OH) 2
6. Calcium + Nitrate
Calcium Nitrate
Ca(NO3) 2
7. Potassium + Nitrite
Potassium Nitrite
K(NO2)
8. Lithium + Carbonate
Lithium Carbonate
LI2(CO3)
9. Potassium + Sulfite
10. Calcium + Phosphate
Potassium Sulfite
K2(SO3)
Calcium Phosphate
Ca3 (PO4)2
11. (NH4) 2O
Ammonium Oxide
12. Ca (OH) 2
Calcium Hydroxide
13. K 2 (SO4)
Potassium Sulphate
14. K3 (PO4)
Potassium Phosphate
15. Be (OH) 2
Beryllium Hydroxide
Bonus – Metals with more than 1 charge 16. Cu(OH)2
Copper II Hydroxide
17. Fe 2 (SO4)3
Iron III Sulfate
18. Hg3(PO4)2
19. Pb(OH)2
Mercury II Phosphate
Lead II Hydroxide
When non-metals combine, a pure substance called a molecule
or a molecular compound is formed.
Molecular compounds differ from ionic compounds in several
ways.
They can be solids, liquids, or gases at room temperature.
They tend to be insulators, or poor conductors of electricity.
They also have relatively low melting and boiling points because
the forces between the molecules are weak.
Examples of molecular compounds:
sugar, acetylene, and water.
Scientists have discovered more than 10 million compounds.
At least 9 million are molecular compounds containing the
element carbon.
WRITING FORMULAS FOR MOLECULAR COMPOUNDS
Writing formulas for molecular compounds is similar to writing
formulas for ionic compounds, except that no ions are present
and the ion charge is not used in the formulas.
This makes it hard to predict how non-metals combine.
However, the formulas still clearly show what elements are
present, and how many of each type of atom make up the
molecule.
For example, hydrogen gas is usually found as H2.
Each molecule has two atoms of hydrogen connected to each
other.
For ammonia ( NH3(g) ), the situation is similar.
Three hydrogen atoms combine with the nitrogen atom.
Naming of Molecular Compounds
Non-metal + Non-metal
1.  The first element in the compound uses the element name
(just like the ionic compounds do).
2. The second element has a suffix – ide
(like the ionic compounds).
3. A prefix is used which tells how many atoms there are.
4. Exception to #3 above – when the first element has only 1
atom the prefix mono is not used.
Examples:
CO2 carbon dioxide
CO carbon monoxide
CCl4 carbon tetrachloride H2O Dihydrogen monoxide
Number of Atoms
1
2
3
4
5
6
7
8
9
10
Prefix
mono
di
tri
tetra
penta
hexa
hepta
octa
nona
deca
Molecular Compounds – Non-metal + Non-metal
CO2
Carbon dioxide
N 2O
Dinitrogen monoxide
N2O3
Dinitrogen trioxide
NF3
Nitrogen trifluoride
CCl4
Carbon tetrachloride
PF5
Phosphorus pentafluoride
S2F4
a. disulfur tetrafluoride
b. carbon trioxide
CO3
c. nitrogen pentoxide
NO5
d. nitrogen tribromide
NBr3
e. dinitrogen heptachloride
f. carbon tetrachloride
N2Cl7
CCl4
g. hydrogen monochloride HCl
h. trihydrogen monophosphide H3P
i. dihydrogen monoxide
H 2O
Comparing Ionic And Molecular Compounds