Ions and Ionic Compounds
Elements combine in a specific ratio to form compounds. Compounds can be categorized
as ionic or covalent depending on the type of bond present within the compound. Ionic
compounds consist of ionic bonds that arise from the electrostatic (magnetic) attraction
between ions (charged species). The positively charged ion, called a cation, and the
negatively charges ion, called an anion are attracted much like two magnets. The bond
found in covalent molecules is a covalent bond which results from two atomic nuclei
sharing electrons.
This exercise is designed to allow you to explore the world of ionic compounds. When
you complete this exercise you should understand:
1. Which elements form cations and which elements form anions.
2. Be able to list all metals that form cations of a specific charge and identify that
charge.
3. Be able to list all elements that form anions and identify the charge they will have.
4. Be able to name cations, anions, and polyatomic ions.
5. Be able to determine the number of protons and electrons in an element and an
ion.
6. Explain the difference between elemental ions and polyatomic ions.
7. Be able to explain what the term charge neutrality means.
8. Be able to write the formula of ionic compounds.
9. Be able to write the name of ionic compounds.
Part I: Ions
A cation results from an element losing an electron (e-) to form a positively charged
species. The magnitude of the charge of the cation depends on the number of electrons
lost.
X → X+ + eX → X2+ + 2eThe number of electrons lost by an element, that forms a cation, equals the electron
difference between that of the element and that of the nearest noble gas or pseudo noble
gas. Example: Sodium, in its neutral state, has 11
protons and 11 electrons. The nearest noble gases are
Neon with 10 electrons and Argon with 18 electrons.
Sodium can either lose one electron to have the same
number of electrons as Neon, or it can gain 7 electrons
to reach Argon. Because the difference between
Sodium and Neon is less, Sodium will lose one
electron. Once sodium has lost an electron the ion will
contain 11 protons but only 10 electrons making the Sodium ion have a 1+ charge.
An anion is the product of an element gaining electrons to become negatively charged.
The magnitude of the charge of the anion depends on the number of electrons gained.
Z + e- → ZZ + 2e- → Z2The number of electrons gained by an element, that forms an anion, equals the difference
between that element and the nearest noble gas. Example: Chlorine has 17 protons and
17 electrons in its neutral state. The nearest
noble gases are Neon with 10 electrons and
Argon with 18 electrons. Chlorine can either
lose 7 electrons to reach Neon or it can gain one
electron to have the same number of electrons
as Argon. Because the difference between
Chlorine and Argon is less, Chlorine will
choose to gain one electron. After the addition
of that electron, Chlorine will have 17 protons
and 18 electrons making the Chlorine ion have a
1- charge.
Part I of this lab allows you to identify the type of element (metal, metalloid, non-metal)
that forms cations. You will find that cations can be of two types. You will identify the
two types of cations and learn how to name them.
Additionally, you will discover that anions can be of two types. One type of anion is
referred to as a polyatomic anion. Poly- meaning many, atomic- meaning atom, hence,
they are many atom ions. A list of polyatomic ions is provided at the end of this exercise.
The elemental ratio, charge and name of each polyatomic ion are set. Alteration of any
single piece of the above information and you alter the ion. The second type of anion is
an elemental anion. You will identify the type of element that forms elemental anions,
identify the periodic trend associated with the charge formed, and learn how to name
these anions.
Part I: Ions
1. Define cation.
2. Define anion.
3. Define ionic bond.
4. Cations are ______________________ charged species that result from the
_________________ of electrons.
5. Anions are ______________________ charged species that result from the
_________________ of electrons.
Separate the cards (symbol up) according to color, elemental symbol,
and charge.
6. Besides hydrogen and the polyatomic ion ammonium, what type of element
forms cations: metal, metalloid, non-metal?
Analyze the elemental symbol side of the pink cards and orange cards
for differences.
7. Describe the difference between the cations represented on the pink cards and
those found on the orange cards.
Flip the pink and orange cards over.
8. Do you notice a difference in how the cations on the pink cards are named
compared to those on the orange cards?
a. A cation for which the charge is constant is named by writing the
_____________________________.
b. A cation that can have more than one charge is named by writing first the
______________________________ followed by the charge as a
___________________________________.
9. Using your text or the notes, list the symbols of all of the elements that form
cations for which the charge is constant, the magnitude of that charge, and the
name of those cations.
10. What periodic trends do you observe for group 1 and group 2 elements?
Analyze the elemental symbol side of the green cards and yellow cards
for differences.
11. Describe the difference between the symbols of anions on the green cards
compared to those on the yellow cards.
12. What type of element form anions: metals, metalloids, or non-metals?
Flip the yellow and green cards over.
13. What do the names of the elemental anions have in common?
14. Using your text or the notes, list the symbols of all elements that form anions, the
magnitude of that charge, and the name of the anion.
15. What periodic trend do you observe with the elemental anions?
16. What type of ions found on the yellow cards?
17. Define polyatomic ion.
Additional Practice
Element
Sodium
Oxygen
Cesium
Barium
Fluorine
Selenium
Phosphorus
Potassium
Radium
Iodine
Atomic
#
Number protons
11
11
#
electrons
in neutral
atom
Will the
element
gain/lose
electrons
during ion
formation
# of
electrons
in ion
Ionic
Charge
Symbol of
Ion
Name of ion
11
Lose
10
+1
Na+
Sodium ion
Part II: Formulas of Ionic Compounds
Ionic compounds are the result of cations combining with anions via an electrostatic
attraction. The ionic compound formed will be neutral. To obtain charge neutrality all
positive charges must be counterbalanced by an equal amount of negative charge.
Example: Sodium ion carries a 1+ charge, the chloride ion carries a 1- charge. When
sodium reacts with chlorine, it does so in a 1:1 ratio making sodium chloride neutral.
Example: Magnesium ion carries a 2+ charge, the oxide ion carries a 2- charge. When
magnesium reacts with oxygen, it does so in a 1:1 ratio making magnesium oxide neutral.
A third example is the reaction of sodium ion with oxide ion. Again sodium has a 1+
charge and the oxide a 2- charge. When sodium combines with oxygen it must do so in a
2:1 ratio to give neutral sodium oxide.
Note: When more than one of an ion is required for the ionic compound to achieve charge
neutrality, a subscript is used to the right of the elemental symbol to indicate the quantity
of that ion necessary. If more than one polyatomic ion is needed for the ionic compound
to achieve charge neutrality then the polyatomic ion is placed in parenthesis and the
number required is written as a subscript outside the parenthesis.
To assist in determining when an ionic compound achieves charge neutrality the ions in
the ionic block set have been designed in such a way so that the size is related to the
magnitude of the charge. Begin by placing the cation of interest on a surface. Then add
anions one by one until the size of the cation row and anion row are equivalent (or at least
really close). Example: A compound of magnesium ion and chloride ion. If you lay the
magnesium ion down followed by one chloride ion, you will notice that the sizes do not
match. Now add a second chloride ion and you will see that the sizes match. That is
because it takes 2 chloride ions of a -1 each to neutralize the charge of one magnesium
ion. Your cards will look as below.
Part III: Naming Ionic Compounds
The name of an ionic compound is simply the combination of the names of the ions. The
name is written with the cation listed first followed by the name of the anion. In this
section of the lab you will practice developing chemical formulas for and naming ionic
compounds. In so doing you will explore the concept of charge neutrality.
For each of the following pairs,
1. Gather the cations and anions of indicated by the first cation/anion pair on the
attached table.
2. Place the cation on your desk with the symbol face up.
3. Starting on a second row, add anions until the length of the anion row is
equivalent to that of the cation row.
4. If in adding anions the anion row becomes longer than the cation row, add an
additional cation and repeat step 3.
5. Fill in the table with your results.
6. Repeat steps 1-5 for each cation and anion pair in the table.
Cation/Anion Symbol Symbol # of
Pair
of the
of the
Cations
Cation Anion
Required
For
charge
neutrality
1
Potassium
and bromide
2
Iron (III) and
oxide
3
Magnesium
and
hydroxide
4
Gold (III)
and sulfate
5
Aluminum
and nitride
6
Copper (II)
and acetate
7
Calcium and
sulfide
8
Sodium and
phosphate
# of
Formula of Name of
Anions
Compound Compound
Required
For
charge
neutrality
Practice Problems
In the table below write the symbols of the positive and negative ions using the periodic table to determine ionic charge. Determine
the number of each ion that will give a charge balance by using the cards to help match positive and negative charges. Write correct
formulas using subscripts to indicate when two or more ions are needed. Write the names of the ionic compounds by placing the
metal name first, then the non-metal name ending in –ide.
Name
Sodium oxide
Magnesium sulfide
Potassium chloride
Calcium nitride
Aluminum bromide
Lithium phosphide
Cadmium nitride
Silver oxide
Positive ion
Negative ion
Formula
Name the following ionic compounds.
Formula
Name
Na2S
ZnF2
MgO
K3N
Ca3P2
AlBr3
Write the ionic formula for the following compounds.
Name
Iron (II) bromide
Copper (I) oxide
Gold (III) nitride
Copper (II) chloride
Gold (I) phosphide
Iron (III) sulfide
Positive ion
Negative ion
Formula
Name the following ionic compounds.
Formula
Name
Cu3P
Fe2O3
FeBr3
CuCl
AuN
Write the ionic formulas for the following compounds containing polyatomic ions.
Name
Sodium acetate
Iron (III) cyanide
Gold (I) dichromate
Calcium hydroxide
Aluminum phosphate
Barium nitrate
Positive ion
Negative ion
Formula
Test Yourself
Name: _________________________________________
In each of the following squares write the formula for the compound and its name.
Cs+
Sr2+
Sc3+
Cr3+
Co2+
Ti4+
Se2-
I-
-
F
C2O42ClO3MnO4PO33-
CrF3
Chromium
(III) fluoride
Ti(C2O4)2
Titanium
(IV) oxalate
Ru3+
Polyatomic Ions
CNOHO22-
cyanide
hydroxide
peroxide
NH4+
H3O+
ammonium
hydronium
Carbon
C2H3O2C2O42-
acetate
oxalate
CO32HCO3-
carbonate
hydrogen carbonate (bicarbonate)
Nitrogen
NO3-
nitrate
Silicon
SiO32-
silicate
Phosphorus
PO43phosphate
HPO42hydrogen phosphate
H2PO4
dihydrogen phosphate
NO2-
nitrite
PO33-
phosphite
Sulfur
SO42HSO4-
sulfate
hydrogen sulfate
SO32HSO3-
sulfite
hydrogen sulfite
Chlorine
ClO3ClO4-
chlorate
perchlorate
ClO2ClO-
chlorite
hypochlorite
Manganese
MnO4-
permanganate
Chromium
CrO42Cr2O72-
chromate
dichromate