Conceptual Physics - Elements and Compounds
Day 1 | Day 2 - 3 | Day 4 | Day 5 | Lab | Reading Assignment

This Unit's
Process Standards: 1.1, 2.1, 3.5, 4.1, 4.2, 4.6, 6.4
Content Standards: 1.1, 1.2, 1.3
Instructional Technology Standards: 2.1, 4.2

vocabulary for the week
  • Chemical symbol
  • Chemical formula
  • Oxidation number
  • Polyatomic ion
  • Binary compound

Elements and Compounds

click to find the answer to today's question How many elements have a chemical symbol with just one letter?

Element link to an Internet Websitecannot be changed by chemical means.
Atom - link to an Internet Websitethe smallest particle of an element.

Chemical symbols - a shorthand for elements.
Compound - two or more elements chemically combined.
Molecule - the smallest particle of a compound.
Chemical formulas - combinations of chemical symbols representing compounds.

 

Use this periodic table to see the common uses for each element.
Alchemists tried to change lead into gold.

Chemical symbols represent elements

Element Symbol Element Symbol Element Symbol
Aluminum Al Bromine Br Calcium Ca
Carbon C Chlorine Cl Chromium Cr
Copper Cu Fluorine F Gold Au
Helium He Hydrogen H Iodine I
Iron Fe Lead Pb Lithium Li
Magnesium Mg Mercury Hg Neon Ne
Nickel Ni Nitrogen N Oxygen O
Phosphorus P Potassium K Silicon Si
Silver Ag Sodium Na Sulfur S
Tin Sn Uranium U Zinc Zn

All elements listed alphabeticallylink to a local webpage

Chemical symbols can be one or two letters. The first letter is always a capital case and the second letter is always a small case. Do not get sloppy when writing chemical symbols.

Learn the chemical symbols for the 30 elements in the table above. You already know many of them. Work on the ones that you don't know.

Use this Periodic Table Game link to an Internet Websiteto learn chemical names.

Day 2 - 3

Writing Chemical Formulas

click to find the answer to today's question What number is never used as a subscript in a chemical formula?
click for a career
Pharmacist

Chemical formulas represent compounds.

Oxidation numbers are used to determine the ratio in which elements combine to form compounds.

Oxidation numbers tell the number of electrons an atom gained or lost when forming the compound.

The plus or minus indicates if electrons were lost or gained.

Since electrons have a negative charge, and atom with a negative oxidation number will gain electrons. That means an atom with a positive oxidation number will lose electrons.

Nonmetals and polyatomic ions almost always gain electrons - have negative oxidation numbers.

Metals almost always lose electrons - have positive oxidation numbers.

The number indicates how many electrons.

Example: Aluminum has an oxidation number of +3. It will lose 3 electrons when forming compounds.

Oxygen has an oxidation number of -2. It will gain 2 electrons when forming compounds.

Common Oxidation Numbers

Element Oxidation # Element Oxidation # Element Oxidation #
Aluminum
Al		 +3 Bromine
Br		 -1 Calcium
Ca		 +2
Carbon
C		 -4 or +4 Chlorine
Cl		 -1 Chromium
Cr		 +3
Copper
Cu		 +2 or +1 Fluorine
F		 -1 Gold
Au		 +3
Helium
He		 0 Hydrogen
H		 +1 Iodine
I		 -1
Iron
Fe		 +3 or +2 Lead
Pb		 +2 Lithium
Li		 +1
Magnesium
Mg		 +2 Mercury
Hg		 +2 Neon
Ne		 0
Nickel
Ni		 +2 Nitrogen
N		 -3 Oxygen
O		 -2
Phosphorus
P		 -3 Potassium
K		 +1 Silicon
Si		 +4
Silver
Ag		 +1 Sodium
Na		 +1 Sulfur
S		 -2
Tin
Sn		 +4 or +2 Uranium
U		 +6 Zinc
Zn		 +2

Notice that some of the elements on the table have more than one possible oxidation number. You will soon learn how to know which one to use. However, the first listed on the table is the most common.

link to a local webpage with useful information

Understanding chemical formulas

  • Chemical formulas are composed of a positive half and a negative half.

    Water is a compound you know to have a formula of H2O.

  • The element with the positive oxidation number is always written first.

    H

  • The element with the negative oxidation number is always written second.

    HO

  • The total of the oxidation numbers in a compound must equal zero.

    Hydrogen's oxidation number is +1 and oxygen's is -2.
    With one H and one O, the total is not 0, it is -1.

  • Subscripts, small numbers to the lower right of the chemical symbol, represent the number of atoms of that element present in the compound.

    The subscript of 1 is never written in a chemical formula.
    It is understood since the chemical symbol is there.
    Add subscripts after a chemical symbol, when needed, to make the oxidation numbers total zero.
    H2O

  • Multiply subscript by oxidation number for the total oxidation number of each element in a formula.

    For hydrogen: (oxidation number +1) (subscript 2) = +2 total
    For oxygen: (oxidation number -2) (subscript 1) = -2 total

  • The formula H2O is the correct formula.  

The easiest way to think of writing chemical formulas is to
use the oxidation number (without the + or -) of one
element as the subscript of the other element.
Example
Remember -   subscripts of 1 are never written in a formula!

After doing this, be sure the subscripts will not reduce.
If both subscripts are divisible by the same number,
they must be reduced to have the formula in its proper form.

Example: Ca2O2 must be reduced to CaO

Practice Writing Chemical Formulas:

Write the formulas for the compounds formed when these elements combine. Do not look at the answers before you have written all the formulas. If one of your formulas differs from the answer, try to find out why. If you have questions, ask your facilitator.

  1. hydrogen and oxygen
  2. sodium and chlorine
  3. chlorine and magnesium
  4. potassium and sulfur
  5. aluminum and oxygen
  6. gold and fluorine
  7. iodine and hydrogen
  8. phosphorus and silver
  9. phosphorus and aluminum
  10. sulfur and silver
  11. oxygen and uranium
  12. tin (IV) and oxygen
  13. iron (III) and oxygen
  14. copper (I) and chlorine
  15. copper (II) and chlorine

Roman numerals indicate the oxidation number of the positive element in problems 12 - 15.


Physical Science

  Answers to 061 practice problems:

  1. H2O
  2. NaCl
  3. MgCl2
  4. K2S
  5. Al2O3
  6. AuF2
  7. HI
  8. Ag3P
  9. AlP
  10. Ag2S
  11. UO3
  12. SnO2
  13. Fe2O3
  14. CuCl
  15. CuCl2

14 elements on the periodic table have chemical symbols with only one letter.

Hydrogen (H), Boron (B), Carbon (C), Nitrogen (N), Oxygen (O), Fluorine (F), Phosphorus (P), Sulfur (S), Potassium (K), Vanadium (V), Yttrium (Y), Iodine (I), Tungsten (W) and Uranium (U)

   

The number 1 is never used as a subscript in a chemical formula.
The chemical symbol represents one atom of the element in a compound.