Nomenclature Flashcards
Explain how to distinguish between an ionic and a covalent compound.
An ionic compound usually consists of a metal cation and an anion, which is either a nonmetal OR polyatomic anion. An exception to this rule of thumb is when the cation is the ammonium ion (NH4+). The compound ammonium chloride (NH4Cl) is ionic even though there is no metal.
A covalent compound consists of nonmetal atoms.
Is the compound barium sulfate BaSO4 ionic or covalent?
Barium sulfate is considered to be an ionic compound because it consists of the barium cation (Ba2+) and the polyatomic nonmetal anion sulfate (SO42-).
Is the compound ammonium phosphate (NH4)3PO4 ionic or covalent?
Ammonium phosphate is considered to be an ionic compound because it consists of the ammonium cation (NH4+) and the polyatomic nonmetal anion phosphate (PO43-). It is important to recognize the ammonium cation as one of the few cations which are not derived from metals.
When is it necessary to use a roman numeral in naming a compound?
A roman numeral is used for an ionic compound when the metal cation can have multiple charges (Fe2+ and Fe3+ for example). The roman numeral indicates the charge. Essentially all transition elements can have multiple charges - with the exception of Zn2+, Cd2+ and Ag+. Other elements that can have multiple charges, which you need to know, are lead (Pb2+ and Pb4+) and tin (Sn2+ and Sn4+).
When is it necessary to use a greek prefix in naming a compond?
A greek prefix is usually used in naming a binary covalent compound. This is because the nonmetals in such compounds can be combined in multiple ratios which are not predictable as with ionic compounds. The greek prefixes are required to indicate how many of each atom in a compound. As an example the following two compounds (NO and N2O) are called nitrogen monoxide and dinitrogen monoxide. Note that if there is only one atom of the first element, the prefix “mono” is not used. Greek prefixes are also used in the naming of some polyatomic ions. For example H2PO4- is called dihydrogen phosphate. Finally, they are used to indicate the number of water molecules in a hydrated compound, such as barium chloride octahydrate (BaCl2 · 8H2O).
What is a hydrate?
Most ionic compounds exist naturally as hydrates. That is the ionic crystals absorb water from the atmosphere in definite molar proportions.For example sodium thiosulfate in its natural state has 5 moles of H2O molecules per 1 formula unit of Na2S2O3. The formula is normally written as Na2S2O3 • 5H2O and is called sodium thihosulfate pentahydrate. The water molecules are loosely bound and can be temrporarily removed by heating (with a bunsen burner for example). If the compound is no longer heated and if the compound is in contact with the atmosphere, it will once again adsorb back the water in the appropriate proportions.
Give the name for the following compound and indicate if it is ionic or covalent: Ag2SO3
Silver sulfite (ionic)
Give the name for the following compound and indicate if it is ionic or covalent: K3PO4
Potassium phosphate (ionic)
Give the name for the following compound and indicate if it is ionic or covalent: CoBr2
Cobalt (II) bromide (ionic)
Give the name for the following compound and indicate if it is ionic or covalent: NBr3
Nitrogen tribromide (covalent)
Give the name for the following compound and indicate if it is ionic or covalent: NaCN
Sodium cyanide (ionic)
Give the name for the following compound and indicate if it is ionic or covalent: FeSO4
Iron (II) sulfate
Give the name for the following compound and indicate if it is ionic or covalent: ICl3
Iodine trichloride (covalent)
Give the name for the following compound and indicate if it is ionic or covalent: KMnO4
Potassium permanganate (ionic and note that the polyatomic anion has a metal + oxygen)
Give the name for the following compound and indicate if it is ionic or covalent: Na2Cr2O7
Sodium dichromate (ionic and note that the polyatomic anion has a metal + oxygen)
