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Unit 4: Naming and Writing Chemical Formulas

The rulebook that turns a formula into a name and a name back into a formula, for ionic compounds, covalent compounds, and acids.

8 topics · 27 questions

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4.1 Naming Binary Ionic Compounds

  1. How it worksHow does naming a binary ionic compound chain the metal's name to the nonmetal's name with an -ide ending?
  2. Worked exampleFind the correct name for the ionic compound MgO.
  3. Worked exampleFind the correct name for the ionic compound CaBr2.
Your turn1 of 2
The ionic compound NaCl is named sodium chloride in every chemistry textbook, never sodium chlorine, even though the second element started out as the gas chlorine before bonding. Why does NaCl get called sodium chloride instead of sodium chlorine?

4.2 Writing Formulas for Ionic Compounds

  1. How it worksHow does crossing over the charges of two ions give you the subscripts in a formula?
  2. Worked exampleFind the correct formula for the ionic compound formed between aluminum and oxygen.
  3. Worked exampleFind the correct formula for the ionic compound formed between magnesium and nitrogen.
Your turn1 of 2
Calcium forms a Ca2+ ion while chlorine forms a Cl- ion, and the resulting neutral compound is written CaCl2, with two chlorine atoms for every one calcium atom rather than a one-to-one ratio. Why does calcium chloride need two chlorine atoms for every one calcium atom?

4.3 Polyatomic Ions and Their Formulas

  1. How it worksHow does a polyatomic ion carry one overall charge even though it's built from several covalently bonded atoms?
  2. Worked exampleFind the formula for calcium phosphate, using the ions Ca2+ and PO4 3-.
  3. Worked exampleFind the formula for ammonium sulfate, using the ions NH4+ and SO4 2-.
  4. Common mistakeWhy doesn't the number of atoms inside a polyatomic ion change when you write a compound's formula?
Your turn1 of 2
A sulfate ion, SO4 2-, is made of one sulfur atom covalently bonded to four oxygen atoms, yet the whole group moves and reacts together as a single charged particle rather than falling apart into separate ions. Why does a group of bonded atoms like sulfate act as a single charged unit instead of falling apart?

4.4 Naming Compounds with Polyatomic Ions

  1. How it worksHow do you recognize a polyatomic ion inside a formula so you can name the compound correctly?
  2. Worked exampleFind the correct name for the compound NH4NO3.
  3. Worked exampleFind the correct name for the compound K2SO4.
Your turn1 of 2
The compound name 'sodium sulfate' immediately tells a chemist that the compound contains Na+ ions paired with SO4 2- ions, without needing to see the actual chemical formula written out. Why does the name sodium sulfate tell you exactly which two ions built the compound?

4.5 Naming Ionic Compounds with Transition Metals

  1. How it worksHow does a roman numeral in a compound's name tell you the exact charge on a transition metal ion?
  2. Worked exampleFind the correct name for the compound FeCl3 using the Stock system.
  3. Worked exampleWalk me through assigning the correct roman numeral when naming the compound CuO with the Stock system.
  4. Common mistakeWhy doesn't every metal need a roman numeral in its compound's name?
Your turn1 of 2
Iron reacts with chlorine to form FeCl2 in one compound and FeCl3 in another, showing that iron doesn't always carry the same ionic charge. Why does iron sometimes form Fe2+ and other times Fe3+ in different compounds?

4.6 Naming Binary Covalent Compounds

  1. How it worksHow do Greek prefixes in a covalent compound's name tell you exactly how many atoms of each element are present?
  2. Worked exampleFind the correct name for the covalent compound N2O5.
  3. Worked exampleFind the correct name for the covalent compound CCl4.
Your turn1 of 2
Carbon monoxide, CO, has one oxygen atom and needs no numerical prefix on carbon, while carbon dioxide, CO2, has two oxygen atoms and requires the prefix di- before oxide. Why does carbon dioxide need the prefix di- while carbon monoxide only has one oxygen?

4.7 Naming and Writing Formulas for Acids

  1. How it worksHow does an acid's name change depending on whether its polyatomic ion ends in -ate or -ite?
  2. Worked exampleFind the correct name for the acid H2SO4.
  3. Worked exampleFind the correct name for the acid HBr once it's dissolved in water.
  4. Common mistakeWhy isn't every compound that contains hydrogen automatically classified as an acid?
Your turn1 of 2
The formula HCl by itself is named hydrogen chloride, but the exact same formula dissolved in water is instead called hydrochloric acid, a different name for what looks like the same substance. Why does HCl get called hydrochloric acid only once it's dissolved in water?

4.8 Distinguishing Ionic from Covalent Compounds

  1. How it worksHow does checking whether a formula contains a metal and a nonmetal predict its bond type?
  2. Common mistakeWhy doesn't a compound's physical state alone tell you whether it's ionic or covalent?
  3. Ties togetherHow does the electron-transfer versus electron-sharing picture from bonding explain why ionic and covalent compounds follow completely different naming rules?
Your turn1 of 2
A chemist glances at a formula like NaCl and immediately identifies it as ionic, while glancing at a formula like CO2 immediately identifies it as covalent, often without running any test at all. Why can you often tell a compound is ionic just by glancing at which elements are in its formula?