Atoms, Molecules, Formulas & Equations
(BASIC BUILDING BLOCKS OF MATTER & LIFE,
 OR . . THE NATURE OF MOTHER NATURE)
Teacher Reference

Objectives:
1. To provide a general understanding of atoms, elements, and compounds
2. To examine word origins of elements and their periodic classification.
3. To combine atoms into molecules, to write and name them.

Materials needed:
  a. Periodic Table of the Elements
  b. set of positive and negative charge cards; one set per group

Selected Answers for Teachers

Activity 1: Elements

3. What do you think are the two different elements that make up the compound
  carbon dioxide? Answer: carbon and oxygen

4. How many total atoms are there in carbon dioxide? Explain. Answer: 3.

5. How can there be only 105 different elements but billions upon billions of atoms?
  Answer: Each of the 105 elements is composed of billions upon billions of atoms.

7. Only four elements make up almost all of a living person. What do you think they
  are? Answer: C, H, O, N.

8. Brimstone is mentioned in the Bible as a foul-smelling, yellow substance. What do
  you think is brimstone? Answer: sulfur mentioned as hell, fire, and brimstone.

Activity 3: A Periodic Table or Classification of the Elements

3. There are more metals than non-metals in the Period Table. Draw a
  line from the top to the bottom in the Periodic Table between the metal
  elements and the non-metal elements. The line is like a stair case. Answer:
  The line runs from top to bottom to the left of elements C, P, Se, I, and Rn.

4. Elements in a group have similar chemical properties and formulas. If fluorine,
  atomic number 9, has the molecular formula of F2, what are the molecular
  formulas for the rest of the elements in this group? Write the formulas in the
  space below. Answer: F2, Cl2, Br2, I2, At2.
6. Elements in the Periodic Table were originally grouped by increasing atomic mass
  or atomic weight. In general, atomic masses increase in a period except in four cases.
  Write the names of the elements in two cases where the masses of the elements are
  reversed in a Period. Answer: Atomic #'s 27 and 28; Atomic #'s 52 and 53;
  Atomic #'s 99 and 100; Atomic #'s 101 and 102.

7. Hydrogen in Group 1 combines with oxygen to form H2O. Write the formulas for all
  of the other elements in Group 1 when they combine with oxygen.
  Answer: Li2O, Na2O, K2O, Rb2O, Cs2O, Fr2O.
8. He (atomic # 2) is a noble or inert gas since it does not combine with anything else.
  Write the symbols and names of the rest of the noble gases that are in the same group.
  Indicate an economic use for at least two of the gases. Answer: Ne, Ar, Kr, Xe, Rn.

Activity 5: Atomic Bonding Within Molecules

4. How can substances become charged? Think of examples in your life.
  Answer: Substances become charged particularly on dry days by walking
  across a rug, combing hair, sliding across a plastic seat cover of a car, etc.

6. Charging a ruler did not cause a chemical reaction but it caused the salt or the
  paper to move toward it. If the ruler is positively charged, what charge must pieces
  of tissue paper and salt have been? Explain. Answer: Negative.

7. If an object is negatively charged and repelled another object, what charge must
  the other object have been? Explain. Answer: Positive.

Activity 6: Introduction to Molecules

1. Suppose that you had an atom with a 3+ charge.
  a. How many atoms with a 1- charge are required
    to make a neutral molecule? Answer: 3

  b. How many total atoms are there in the neutral molecule?
    Answer: 4 

 c. Make a drawing of the molecule in the space
   the right using circles for atoms. Be sureto
   show charges within each circle.


2. Complete the following table by filling in the blanks. Answers: 2+ + 2- --> PN;  
  2(3+) + 3(2-) --> P2N3;   3+ + 3(1-) --> PN3; etc.

3. Complete the following table by filling in the blanks. Instead of charge cards, atoms
  with their actual charges are shown. Write the number of atoms in front of atoms as
  needed. A subscript is the number of positively or negatively charged elements.
  Subscripts of 1 are understood and are not written.
  Answers: Ca2+ + O2- --> CaO;   2Al3+ + 3O2- --> Al2O3;   2H1+ + O2- --> H2O;
  2K1+ + O2- --> K2O;   Mg2+ + 2Cl1- --> MgCl2.

4. Just as people have different tastes in food, clothes, etc., nitrogen atoms exhibit
  different charges when they react with oxygen to form smog molecules in a hot car
  engine. Complete the table by writing the correct formulas of possible NxOy
  molecules in the blanks in the table below.
 
atoms
N1+ and O2-
N2+ and O2-
N4+ and O2-
N5+ and O2-
N3- and O2-
formula
N2O
NO
NO2
N2O5
not possible two negative charges

Activity 7: Charges or Oxidation Numbers

3. Think of one or more chemical reactions that are started with heat.
  Answer: Anything that burns or is oxidized.

4. Why are drivers cautioned not to smoke when pumping gasoline at a gas station?
  Answer: The lighted cigarette could ignite gasoline.

5. Think of a chemical reaction that is started when something is struck.
  Answer: Dynamite, the firing of a rifle shell.

6. Think of a chemical reaction that is started when something is scratched or rubbed.
  Answer: A match. An infection on your skin.

7. Examine charges of each pair of elements. Write the formula of the neutral molecule;
  the subscripts show the number of atoms needed to make the molecule neutral.
  Subscripts of 1 are understood and need not be placed in the formula. Name the
  compound using the names from above; positive elements are written and named
  first. Negatively charged elements have a different name than when they are neutral
  (as shown above in parentheses).

element and charge
Cl1-
O2-
N3-
Na1+
NaCl
Na2O
Na3N
name of compound
sodium chloride
sodium oxide
sodium nitride
Ca2+
CaCl2
CaO
Ca3N2
name of compound
calcium chloride
calcium oxide
calcium nitride
Al3+
AlCl3
Al2O3
AlN
name of compound
aluminum chloride
aluminum oxide
aluminum nitride

Activity 8: Charges or Oxidation Numbers of Group of Atoms

1. Examine charges of each pair, write the formula and the name of the compound
  using names from above; positive elements or radicals are written and named first.

atom or ion
HCO31-
SO42-
PO43-
Na1+
NaHCO3
Na2 SO4
Na3 PO4
name of compound
sodium bicarbonate
sodium sulfate
sodium phosphate
Ca2+
Ca(HCO3)2
CaSO4
Ca3 (PO4)2
name of compound
calcium bicarbonate
calcium sulfate
calcium phosphate
Al3+
Al(HCO3)3
Al2 (SO4)3
AlPO4
name of compound
aluminum bicarbonate
aluminum sulfate
aluminum phosphate

2. Write the formula for ammonium sulfate, a fertilizer. Answer: (NH4)2 SO4

Activity 9: Naming Compounds

1. The formula for water can be H2O or HOH. What are two possible chemical names?
  Answer: Although water is the common and preferred name, other possibilities
  are: hydrogen monoxide, dihydrogen monoxide, dihydrogen oxide, hydrogen oxide,
  hydrogen hydroxide.

2. Name the compounds below using Rule 2.

formula
name
formula
name
N2O
dinitrogen monoxide
or dinitrogen oxide
NO
nitrogen monoxide
also known as nitric oxide
NO2
nitrogen dioxide
N2O4
dinitrogen tetroxide
N2O5
dinitrogen pentoxide
NH3
trihydrogen nitride
commonly known as ammonia
CO
carbon monoxide
CO2
carbon dioxide
 
Comments: The naming of compounds differs slightly since there are both formal and
  common names. Compounds such as water, ammonia, cholesterol, etc., are known
  by these common names. Authors often do not apply prefixes for the element H in
  compounds; one example is hydrogen sulfide (H2S). A prefix is also not used for
  oxides unless more than one compound exists such carbon monoxide and carbon dioxide.

3. Name the compounds below using Rule 3.

formula
name
formula
name
NH4Cl
ammonium chloride
CaCO3
calcium carbonate
KClO3
potassium chlorate
Na3PO4
sodium phosphate sold in stores as TSP or trisodium phosphate
H2SO4
dihydrogen sulfate
also known as sulfuric acid
NaHCO3
sodium bicarbonate sold in grocery stores as baking soda

4. Use all three rules to complete the table; supply either the rule, a formula, or name.

rule(s)
formula
name of compound
1
MgCl2
magnesium chloride
2
H2O
dihydrogen monoxide
3
(NH4)2SO4
diammonium sulfate
3
Na3PO4
sodium phosphate
2
SO3
sulfur trioxide
3
Al2 (SO4)3
aluminum sulfate
3
KOH
potassium hydroxide
1
Fe2O3
iron oxide
3
Al2 (CO3)3
aluminum carbonate

Comments: Metal compounds with iron that have both a 2+ and 3+ charge are
  formally named as iron (II) or iron (III). For example: FeO is iron (II) oxide, whereas
  Fe2O3 is iron (III) oxide.

Activity 10: Using a Dichotomous Key to Name Compounds

Use the dichotomous key above to key out the names of the compounds in the table.


formula
name of compound
formula
name of compound
FeCl3
iron chloride
or iron (III) chloride
CCl4
carbon tetrachloride
H2CO3
dihydrogen carbonate
or carbonic acid
Al2O3
aluminum oxide
CaSO4
calcium sulfate
Mg3P2
magnesium phosphide
NaHCO3
sodium bicarbonate
or baking soda
NH4NO3
ammonium nitrate
KOH
potassium hydroxide
CaC2
calcium carbide
 

Activity 11: Balancing Chemical Equations

3. Complete the table involving H2 and O2 to form water (H2O). The subscript tells us
  how Mother Nature put atoms together to make molecules. Balance the equation by
  supplying the coefficients in the boxes provided. Coefficients of 1 are not written; show
  this by leaving a square empty. The equation is balanced when the number of atoms
  is on both sides of the arrow. The drawing shows molecules in the balanced equation.
reactants
-->
products
balanced
equation
2 H2   +   O2
-->
2 H2O
# atoms when balanced
4 H and 2 O
-->
4 H and 2 O

4. Complete the following partially completed table involving nitrogen and hydrogen
  gases. The equation is balanced when the number of different atoms are equal on
  both sides of the equation. Draw molecules in the balanced equation.
   

5. Complete the following partially completed table involving aluminum and copper
  chloride. The equation is balanced when the number of different atoms are equal
  on both sides of the equation. Draw molecules in the balanced equation.

  

6. Balance each of the following equations by placing coefficients into the box in front
  of atoms and molecules. A coefficient of 1 does not need to be written. Make a
  drawing of the reaction by completing the boxes.

question
reactants
-->
products
1
2 H2O2
-->
2 H2O   +   O2
2
Zn   +   2 HCl
-->
ZnCl2   +   H2
3
2 CuO  +    C
-->
CO2   +  2 Cu
4
2 Zn   +   O2
-->
2 ZnO
5
H2    +    Cl2
-->
2 HCl
6
CH4  +   2 O2
-->
CO2   +  2 H2O
7
2 AgNO3  +   CaCl2
-->
Ca(NO3)2   +  2 AgCl
8
2 NH3   +   3 Mg
-->
3 H2   +   Mg3N2

VOCABULARY

1.  element: A substance composed of atoms of only one kind that cannot be broken
    down into smaller substances in the laboratory.

2.  compound: A substance that is made up of two or more elements

3.  atom: The smallest particle of an element with the properties of that element.

4.  atomic symbol: Composed of one or two letters that have been assigned to
    represent that particular element. The first letter is always a capital. If there is a
    second letter, it is always lower case.

5.  atomic number: The number of protons or positive charges that each atom of this
    element has in its nucleus. The atomic number determines the identity of an atom.

6.  Periodic Table of the Elements: Arrangement of elements in order of their atomic
    number which is also the number of protons (positively charged particles) in the nucleus.

7.  period: Arrangement of the elements in the Periodic Table into rows.

8.  group: Arrangement of the elements in the Periodic Table into columns.

9.  noble or inert gas: An element which does not combine with anything else under
    ordinary laboratory conditions.

10. molecule: A neutral substance made up of two or more atoms that are attracted to
    one another because of their equal and opposite charges.

11. molecular formula: Shows the combination of different atoms within a molecule
    by their atomic symbols.

12. law of charges: The statement expressing the observation that opposite charges
    attract and move toward one-another and like charges repel or move away from
    one-another.

13. subscript: The number of atoms in a molecule written as a small number after a
    symbol. A symbol of 1 is not written but understood to represent one atom.

14. charge or oxidation number: A charge that an atom accepts in a chemical
    reaction in the formation of a molecule.

15. polyatomic ion: Groups of atoms that join and act as a unit with a single charge.

16. prefix: The use of words such as mono, di, tri, tetra, penta, etc., identify the
    numbers 1, 2, 3, 4, 5, etc. of nonmetals in a molecular formula.

17. dichotomous key: To proceed in a chart either to the right or to the left.

18. reactant: Atoms or molecules at the beginning or to the left side of the ý in a
    chemical equation.

19. product: Atoms or molecules at the end or to the right side of the ý in a
    chemical equation.

20. coefficient: The number in front of an atom or a molecule to tell how many there
    are of each kind.

(C) "Armchair Chemistry for the Middle Grades 2001"