Writing and Naming Compounds

Writing Compounds To write a formula for a compound, you need information You need to know the elements involved You need to know the number of electrons they lose, share, or gain to become stable. This is called the elements oxidation number. The net charge of a compound is 0. Ionic compounds are formed between metals and nonmetals. Covalent compounds are formed between nonmetals.

Oxidation Number For ionic compounds, the oxidation number is the same as the charge on the ion In salt, the sodium ion has a charge of 1+ and the chlorine ion has a charge of 1- The oxidation number of sodium is 1+ and for chlorine, 1-.

Writing and Naming Ions When an atom loses or gains an electron, it becomes an ion The charge of an ion is written in superscript after the elements symbol. Ex. Mg 2+ For the non transition metals, the ion formed depends on the number of outer shell electrons and how likely it is to gain or lose them. Transition metals can have multiple ionic charges, and are given in parenthesis after the element. Ex. Copper (III)

Naming Binary Ionic Compounds Write the name of the positive ion Determine if it is capable of forming more than one oxidation number. If it is, determine the oxidation number from the compound formula and write the charge of the ion in roman numerals after the ion’s name. If it only has one oxidation number, do nothing. Write the root name of the negative ion and add ide to it.

Element-ide Name OxygenOxide PhosphorusPhosphide NitrogenNitride SulfurSulfide FluorineFluoride

Example What would be the name of the compound CuCl? Write the name of the positive ion in the compound: copper Determine if copper is capable of forming more than one oxidation state. Is it a transition metal? Yes. Looking at the formula there is one copper and one chlorine atom. Since the overall charge must be zero and the charge of chlorine is 1-, the charge of copper must be 1+, so write a (I) after copper: copper (I) The root of chlorine is chlor, so it becomes chloride. copper (I) chloride

Example What would be the name of the compound AlCl 3 ? Write the name of the positive ion in the compound: aluminum Determine if aluminum is capable of forming more than one oxidation state. Is it a transition metal? No: aluminum The root of chlorine is chlor, so it becomes chloride. aluminum chloride

Writing Binary Ionic Compounds Write the symbol of the element or polyatomic ion (ions containing more that one atom) that has a positive oxidation number and charge. Write the symbol of the element or polyatomic ion with the negative oxidation number. The charge without the sign becomes the subscript of the other ion.

Example What is the formula for lithium nitride? The symbol and oxidation number of the positive element: Lithium -> Li 1+ The symbol and oxidation number of the negative element: Nitrogen -> N 3- The charge without the sign becomes the subscript of the other: Li 1+ N 3- -> Li 3 N 1

Example What is the formula for lead (III) oxide? The symbol and oxidation number of the positive element: lead -> Pb 3+ The symbol and oxidation number of the negative element: oxygen -> O 2- The charge without the sign becomes the subscript of the other: Pb 3+ O 2- -> Pb 2 O 3

Polyatomic Ions A polyatomic ion is a positvly or negativly charged, covalentyl bonded group of atoms These ions behave as a group like a single ion ChargeNameFormula 1+ammoniumNH acetateC2H3O2-C2H3O2- 1-chlorateClO hydroxideOH - 1-nitrateNO carbonateCO sulfateSO phosphatePO 4 3-

Writing Polyatomic Ions When writing a polyatomic ion, the only difference is adding parentheses around the ion and putting any subscripts at the parentheses

Example What is the formula for barium chlorate? The symbol and oxidation number of the positive element: barium -> Ba 2+ The symbol and oxidation number of the negative polyatomic ion: chlorate -> ClO 3 1- The charge without the sign becomes the subscript of the other: Ba 2+ ClO > Ba(ClO 3 ) 2

Binary Covalent Compounds Covalent compounds are formed between nonmetals. Some nonmetals can form multiple compounds with one another. Covalent compounds are named differently than ionic compounds Nitrogen and oxygen can form N2O, NO, No2, and N2O5. If they were named like ionic compounds they would all be called nitrogen oxide.

Using Prefixes With covalent compounds a prefix is used to indicate how many atoms of an element are in a compound. Often the mono- prefix is omitted, but is used as an emphasis in some cases like carbon monoxide Number of Atoms Prefix 1mono- 2di- 3tri- 4tetra- 5penta- 6hexa- 7hepta- 8octa-

NO nitrogen oxide NO2 nitrogen dioxide N2O dinitrogen monoxide N2O5 Dinitrogen pentoxide Number of Atoms Prefix 1mono- 2di- 3tri- 4tetra- 5penta- 6hexa- 7hepta- 8octa-