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Name and Formula of Cations Introductory Chemistry Tutorial

Key Concepts

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Writing the Formula of a Monoatomic Cation Using Its Name

The formula of a monoatomic cation is made up of two parts:

Formula of Monoatomic Cation
symbol of element charge as a superscript to the right of the symbol
E x+

Note the charge on the cation is given with the number first followed by the plus sign.

Ex+   NOT   E+x

Note: if the charge on the cation is 1+, we don't need to write the number 1, that is, E1+ is written as E+

To write the formula of a monoatomic cation when you know the name of the cation:

  1. Split the name of the monoatomic cation up into its two parts:

    (i) name of the element

    (ii) charge on the cation

    name (x+)

  2. Use the periodic table of the elements to find the symbol of the element using its name

    Write the symbol of the element under its name

    name (x+)
    E  

  3. Remove the parentheses from around the charge on the cation:

    (x+) becomes x+

  4. Write this charge as a superscript to the right of the symbol of the element:

    name (x+)
    E x+

  5. Write the formula for the cation:

    Note: if the charge on the cation is 1+, we don't need to write the number 1, that is, E1+ is written as E+

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Worked Examples: Writing the Formula of a Monoatomic Cation

Question 1: Write the formula for the cation with the name potassium(1+)

Solution:

  1. Split the name of the monoatomic cation up into its two parts:

    (i) name of the element : potassium

    (ii) charge on the cation : 1+

    potassium (1+)

  2. Use the periodic table of the elements to find the symbol of the element using its name

    Write the symbol of the element under its name

    potassium (1+)
    K  

  3. Remove the parentheses from around the charge on the cation:

    (1+) becomes 1+

  4. Write this charge as a superscript to the right of the symbol of the element:

    potassium (1+)
    K 1+

  5. Write the formula for the cation: K+

    Note: the charge on the cation IS 1+, so we don't need to write the number 1

Question 2: Write the formula for the cation with the name chromium(3+)

Solution:

  1. Split the name of the monoatomic cation up into its two parts:

    (i) name of the element : chromium

    (ii) charge on the cation : 3+

    chromium (3+)

  2. Use the periodic table of the elements to find the symbol of the element using its name

    Write the symbol of the element under its name

    chromium (3+)
    Cr  

  3. Remove the parentheses from around the charge on the cation:

    (3+) becomes 3+

  4. Write this charge as a superscript to the right of the symbol of the element:

    chromium (3+)
    Cr 3+

  5. Write the formula for the cation: Cr3+

    Note: the charge on the cation is NOT 1+, so we need to write the number 3

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Naming a Monoatomic Cation Using Its Formula

The name of a monoatamic cation is made up of two parts:

Systematic IUPAC Name of Monoatomic Cation
name of element (charge in parentheses given to the right of the name)
element (x+)

Note there is no space between the name of the element and the parentheses.

element(x+)   NOT   element (x+)

To name a monoatomic cation when you know its formula:

  1. Split the formula up into its two parts:

    (i) symbol of the element

    (ii) charge on the cation

    E x+

  2. Use the periodic table of the elements to find the name of the element using its symbol

    Write the name of the element under its symbol

    E x+
    name  

  3. Write the charge on the cation inside parentheses to the right of the element's name:

    E x+
    name (x+)

  4. Write the name of the cation:

    (i) If the charge in parentheses is +, (+), then we MUST write the number 1 to the left of the plus sign, that is, (1+)

    (ii) DO NOT put a space between the last letter of the name and the parentheses:

    name(x+)   NOT   name (x+)

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Worked Examples: Naming a Monoatomic Cation

Question 1: Name the cation that has the formula Na+

Solution:

  1. Split the formula up into its two parts:

    (i) symbol of the element : Na

    (ii) charge on the cation : +

    Na +

  2. Use the periodic table of the elements to find the name of the element using its symbol

    Write the name of the element under its symbol

    Na +
    sodium  

  3. Write the charge on the cation inside parentheses to the right of the element's name:

    Na +
    sodium (+)

  4. Write the name of the cation: sodium(1+)

    (i) The charge in parentheses IS +, (+), so we MUST write the number 1 to the left of the plus sign, that is, (1+)

    (ii) DO NOT put a space between the last letter of the name and the parentheses

Question 2: Name the cation that has the formula Mg2+

Solution:

  1. Split the formula up into its two parts:

    (i) symbol of the element : Mg

    (ii) charge on the cation : 2+

    Mg 2+

  2. Use the periodic table of the elements to find the name of the element using its symbol

    Write the name of the element under its symbol

    Mg 2+
    magnesium  

  3. Write the charge on the cation inside parentheses to the right of the element's name:

    Mg 2+
    magnesium (2+)

  4. Write the name of the cation: magnesium(2+)

    (i) The charge in parentheses is not +, (+), but we MUST still write the number 2 to the left of the plus sign, that is, (2+)

    (ii) DO NOT put a space between the last letter of the name and the parentheses

Footnotes: reference "Nomenclature of Inorganic Chemistry: IUPAC Recommendations 2005" (Red Book)

(1) monoatomic or monotomic or monatomic? The IUPAC document cited above uses monoatomic so we will too!

(2) This location around the symbol of an element is actually referred to as the "right upper index".

left upper index symbol right upper index
left lower index right lower index

(3) Each isotope of hydrogen has been named:
1H is protium, 2H is deuterium, 3H is tritium
(the combination of a muon and an electron behaves like a light isotope of hydrogen and is called muonium, Mu)
The respective cations are:
1H+ is protium(1+) or proton, 2H+ (or D) is deuterium(1+) or deuteron, 3H+ or (T) is trituim(1+) or triton
(Mu+ is muon)
The term "proton" is commonly used to refer to the cation of the undifferentiated mixture of hydrogen isotopes as found in nature.
IUPAC recommends the name hydron in preference to proton to remove any ambiguity when referring the undifferentiated mixture of hydrogen isotopes.
That is, the name of H+ is hydrogen(1+) or hydron.

(4) Heteropolyatomic cations are usually named either substitutively or additively.
Substitutive names do not require a charge number because the name itself implies the charge.
Azanium is the name for NH4+ using substitutive nomenclature.

(5) Hydronium is no longer an acceptable IUPAC name for H3O+
Oxidanium is the name for H3O+ using substitutive nomenclature.

(6) Homopolyatomic cations are named by adding the charge number to the stoichiometric name of the corresponding neutral species.
This is done by adding the appropriate multiplicative prefix (di = 2) to the name of the element (mercury)
Hg22+ is therefore named as dimercury(2+)