Nomenclature

Question 1

Explain how to distinguish between an ionic and a covalent compound.

Answer 1

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.

Question 2

Is the compound barium sulfate BaSO₄ ionic or covalent?

Answer 2

Barium sulfate is considered to be an ionic compound because it consists of the barium cation (Ba²⁺) and the polyatomic nonmetal anion sulfate (SO₄^2-).

Question 3

Is the compound ammonium phosphate (NH₄)₃PO₄ ionic or covalent?

Answer 3

Ammonium phosphate is considered to be an ionic compound because it consists of the ammonium cation (NH₄⁺) and the polyatomic nonmetal anion phosphate (PO₄^3-). It is important to recognize the ammonium cation as one of the few cations which are not derived from metals.

Question 4

When is it necessary to use a roman numeral in naming a compound?

Answer 4

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⁺).

Question 5

When is it necessary to use a greek prefix in naming a compond?

Answer 5

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).

Question 6

What is a hydrate?

Answer 6

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.

Question 7

Give the name for the following compound and indicate if it is ionic or covalent: Ag₂SO₃

Answer 7

Silver sulfite (ionic)

Question 8

Give the name for the following compound and indicate if it is ionic or covalent: K₃PO₄

Answer 8

Potassium phosphate (ionic)

Question 9

Give the name for the following compound and indicate if it is ionic or covalent: CoBr₂

Answer 9

Cobalt (II) bromide (ionic)

Question 10

Give the name for the following compound and indicate if it is ionic or covalent: NBr₃

Answer 10

Nitrogen tribromide (covalent)

Question 11

Give the name for the following compound and indicate if it is ionic or covalent: NaCN

Answer 11

Sodium cyanide (ionic)

Question 12

Give the name for the following compound and indicate if it is ionic or covalent: FeSO₄

Answer 12

Iron (II) sulfate

Question 13

Give the name for the following compound and indicate if it is ionic or covalent: ICl₃

Answer 13

Iodine trichloride (covalent)

Question 14

Give the name for the following compound and indicate if it is ionic or covalent: KMnO₄

Answer 14

Potassium permanganate (ionic and note that the polyatomic anion has a metal + oxygen)

Question 15

Give the name for the following compound and indicate if it is ionic or covalent: Na₂Cr₂O₇

Answer 15

Sodium dichromate (ionic and note that the polyatomic anion has a metal + oxygen)

Question 16

Give the name for the following compound and indicate if it is ionic or covalent: Hg₂S

Answer 16

Mercury (I) sulfide (ionic)

Question 17

Give the name for the following compound and indicate if it is ionic or covalent: Zn(NO₃)₂

Answer 17

Zinc nitrate (ionic)

Question 18

Give the name for the following compound and indicate if it is ionic or covalent: Ba(NO₂)₂

Answer 18

Barium nitrite (ionic)

Question 19

Give the name for the following compound and indicate if it is ionic or covalent: P₂O₅

Answer 19

Diphosphorus pentaoxide (covalent)

Question 20

Give the name for the following compound and indicate if it is ionic or covalent: MgI₂

Answer 20

Magnesium iodide (ionic)

Question 21

Give the name for the following compound and indicate if it is ionic or covalent: FeCl₃ • 6H₂O

Answer 21

Iron (III) chloride hexahydrate (ionic)

Question 22

Give the name for the following compound and indicate if it is ionic or covalent: NH₃

Answer 22

ammonia (covalent)