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Naming Binary Covalent Compounds

Key Concepts

Binary means 2.
A binary covalent compound is a covalent compound made up of 2 different elements.

Naming Binary Covalent Compounds

  • The first element in the formula is named first using the name of the element.
    Symbol in FormulaCNOFPSClBrIH

  • The second element in the formula is named last and using the suffix 'ide'.
    Symbol in FormulaCNOFPSClBrI

    If the compound contains oxygen it will be named as an oxide UNLESS the compound contains oxygen and fluorine in which case it will named as a fluoride.

  • If there is more than one atom of an element in the compound, prefixes are used:
    Number of atoms
    of the element
    (the final vowel of the prefix is usually omitted if it sounds the same as the first letter in the name of the element, eg, monoxide not monooxide, but nitrogen triiodide not nitrogen triodide)
  1. The mono prefix is not usually used for the first named element and sometimes other prefixes are also omitted from the name of the first element.
    The mono prefix may be used if there is more than compound possible, eg, CO and CO2 are both possible oxides of carbon, CO is named carbon monoxide and CO2 is named carbon dioxide.
  2. Some compounds containing hydrogen have special names:
  3. Organic (carbon) compounds have their own naming system.

Formula of Binary Covalent Compounds

  • The first part of the formula will be the symbol for the less electronegative element.
    The less electronegative element is usually named first, so, the symbol for the first named element is written first.
    In general, an element to the left in the Periodic Table is less electronegative than one to the right in the Periodic Table (oxygen is an exception, it is more electronegative than all the other elements except fluorine).
    In general, elements at bottom of a Group in the Periodic Table are less electronegative than the elements at the top of the Group.

    nitrogen becomes N, sulfur beomes S, chlorine becomes Cl etc

  • The second part of the name will include the name of the element but ending end in 'ide', use the symbol for the element indicated:
    oxide indicates oxygen, O, sulfide indicates sulfur, S, chloride indicates chlorine, Cl, etc

  • The prefixes for each element in the name are converted to subscript numbers in the formula:
    eg, dinitrogen = N2, trinitrogen = N3, etc
    eg, dioxide = O2, trioxide = O3, tetroxide = O4 etc
    Since the mono prefix is rarely used, assume if no prefix is present there is only one atom of that element present.

Example : Naming Binary Covalent Compounds

Name the compound with the formula NO2

  1. Identify the elements making up the formula:

    N is the symbol for nitrogen
    O is the symbol for oxygen

  2. Determine which of the elements will be named first:

    N lies to the left of O in the Periodic Table so it is less electronegative than O so nitrogen is named first.
    O is more electronegative so it is named last and given the 'ide' suffix, ie, oxygen becomes oxide.
    The name (without prefixes) looks like nitrogen oxide.

  3. Use the number of atoms of each element present in the formula to find the prefixes:

    N has no subscript so the prefix would be mono (but mono is not usually used), the first part of the name will be nitrogen.
    O2 tells us there are 2 atoms of oxygen present, the prefix will be di and the last part of the name will be dioxide.

  4. Combine the first part of the name with the second part of the name:

    nitrogen dioxide is the name given to the formula NO2

Example : Writing the Formula of Binary Covalent Compounds

Write the formula for sulfur dioxide

  1. Find the symbol of each element present in the formula:

    sulfur has the symbol S
    oxide means oxygen is present and oxygen has the symbol O

  2. Use the prefixes in the name to determine the number of atoms of each element present:

    sulfur has no prefix, probably only 1 atom of sulfur is present, S
    oxide has the prefix di so 2 atoms of oxygen are present, O2

  3. Determine the order of the elements in the formula:

    S is less electronegative than O since it lies below O in the same Group of the Periodic Table, so S comes first in the formula
    O2 must come second in the formula

  4. Combine the first part of the formula with the second part:

    SO2 is the formula for sulfur dioxide

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