Electron Dot structures
Valence electrons of Elements
A Lewis Dot structure or an electron dot structure shows the valence electrons that an atom has in its
highest energy level. The valence electrons can be donated or accepted in chemical reactions. This
changes the chemical structure of the atom.
Directions: Draw the electron dot structures for the following elements.
Sodium
Aluminum
Oxygen
Iodine
Nitrogen
Carbon
Neon
Calcium
Argon
Valence electrons for compounds
The octet rule says that: ________________________________________________________________.
This means that metals tend to _________ electrons and non-metals tend to _____________ electrons.
When two atoms are connected by an electrical charge, there is a ____________ formed between them.
In an ionic bond forms when one atom or element donates electrons to another atom or element. An
ionic bonds hold together ionic compounds.
Directions: Draw the electron dot structures for the following compounds.
Hydrogen Fluoride (HF)
Sodium chloride (NaCl)
Magnesium oxide (MgO)
Potassium iodide (KI)
Calcium chloride (CaCl2)
Hydrochloric Acid (HCl)
Aluminum oxide (Al2O3)
Calcium Flouride (CaF2)
Lithium Oxide (Li2O)
Chemical formulas for compounds
Notice that the electrons have to balance out the charge of ionic compounds. Ionic Compounds have a
neutral (no charge) because the positive charge on the cation is equal to the negative charge on the
anion.
Directions: Determine the Chemical formula for the following compounds.
1. potassium iodide __________________________________________
2. magnesium oxide __________________________________________
3. aluminum chloride __________________________________________
4. lithium sulfide __________________________________________
5. beryllium phosphide __________________________________________
6. calcium chloride __________________________________________
7. aluminum oxide __________________________________________
8. ammonium chloride __________________________________________
Polyatomic ions
Most of the compounds that you have seen so far are one element ionically bonded to another element.
However sometimes electrons can he shared. Non-metals have a high electronegativity, so are able to
hold electrons to the nucleus very well. So, non-metals can share electrons. When nonmetals share
electrons it is called a COVALENT BOND. We will talk more about covalent bonds later, but a group of
non-metals that is bonded together can form an ion (an atom with a positive or negative charge). For
example when oxygen bonds with hydrogen it forms a hydroxide ion (OH-). Here is a list of some
important polyatomic ions.
Table 1: Cations (+1 Charge)
Ion
Two-Dimensional
Structure
Three-Dimensional
Representation
Ammonium
NH4+
Hydronium
H3O+
Table 2: Anions (-1 Charge)
Ion
Two-Dimensional
Structure
Three-Dimensional
Representation
Bicarbonate
HCO3
Cyanide CN
Hydrogen
Sulfate
HSO4
Hydroxide
OH
Nitrate NO3
Nitrite NO2
-
-
Perchlorate
ClO4
Permanganate
MnO4
Table 3: Anions (-2 Charge)
Ion
Carbonate
CO32
Chromate
CrO42
Dichromate
Cr2O72
Two-Dimensional
Structure
Three-Dimensional Representation
Hydrogen
Phosphate
HPO42
Sulfate
SO42
Sulfite
SO32
Thiosulfate
S2O32
Table 4: Anions (-3 Charge)
Ion
Two-Dimensional
Structure
Three-Dimensional
Representation
Phosphate
PO43
Directions: look at the charges on the Polyatomic Ions. Now try to write the chemical formula for the
ionic compounds with polyatomic ions.
1. sodium nitrate __________________________________________
2. calcium carbonate __________________________________________
3. lithium sulfate __________________________________________
4. magnesium hydroxide _________________________________________
5. sodium phosphate __________________________________________
6. aluminum carbonate __________________________________________
7. sodium cyanide __________________________________________