4.2: NAMES AND FORMULAS OF COMPOUNDS

Pages 184-201

NAMES AND FORMULAS OF IONIC COMPOUNDS

Ionic Compounds: can be represented by: name and/or chemical formula

1. Name:- always a metal (+ ion) followed by non-metal (- ion)- the non-metal ion always ends in the suffix “ide”:

Eg: aluminum fluoride

2. Chemical Formula: subscripts indicate the ratio of (+) to (-) ions present in a compound.

Eg: AlF3

YOUR TURN!!!

Name the following ionic compounds:#1. Li2N

Answer: lithium nitride

#2. GaI3Answer: gallium iodide

#3. Fe2O3

Answer: iron oxide#4. In what ratio do the atoms of each compound combine?

WRITING FORMULAS OF BINARY IONIC COMPOUNDS Ionic compounds containing only 2 elements:

positive charges balance the negative charges

Example: aluminum fluorideStep #1: Identify each ion and its charge:Al3+

F-

Step #2: determine total charges needed to balance positive and negative.

Al 3+: = +3F 1- : -1 -1 -1 = - 3

*Charge is balanced when the overall charge equals 0.

CONT’D

Step #3: Note the ratio of positive ions to negative ions:1 Al3+ ion 3 F- ions

Step 4: Use subscripts to write the formula:

AlF3

*Subscripts must be written in lowest terms.

COMPOUNDS CONTAINING A MULTIVALENT METAL

Recall: Multivalent metals can form 2 or more different positive ions.

The periodic table lists the most common ion charge first.

Examples: Look at your periodic table. A) What are the charges of Nickel, Copper &

Manganese?B) Which charge is each element most likely

found within a compound?

NAMING A MULTIVALENT METAL

In order to distinguish between multivalent metals, each ion needs its own specific name.

Roman numerals are used to indicate an ions charge.

I – VII are used to show ion charges 1+ to 7+

I, II, III, IV, V, VI, VII

HOW TO SHOW THE CHARGE WHEN NAMING A MULTIVALENT METAL

For example look at Ni:Ni can form two different ions: Ni2+ or

Ni3+

Therefore in an ionic compound Ni can be written as:

nickel (II) or nickel (III)

When read aloud, they read as follows: nickel two and nickel three

WHAT ROMAN NUMERALS REVEAL ABOUT AN ION OF A METAL

1. Indicates that there is more than one ion for that metal (multivalent).

2. Tells you the exact charge of the metal ion.

(See page 189 for examples)

HOW TO WRITE THE CHEMICAL FORMULA CONTAINING MULTIVALENT ATOM

Write the formula for the compound: Chromium (III )bromide:

Step 1 - Identify each ion and its charge:chromium (III): Cr3+

Bromide: Br –

Step 2 - Determine the total charges needed to balance the charge:

Cr3+: = + 3Br - : -1 -1 -1 = - 3

Step 3 - Note ratio of positive to negative ions:1 Cr3+ ion for every 3 Br – ions

Step 4 – Use subscripts to write formula (a “1” is never shown):

CrBr3

NAMING A MULTIVALENT COMPOUNDWhat is the name of the following compound? Au3N

Step 1 – Identify the Metal: gold (Au)

Step 2 – Check the periodic table to see if it is multivalent:

YES: Au3+ and Au +

Step 3 – Determine the ratio of the ions in the formula:

Au3N = 3 gold ions for every 1 nitride ion.

Step 4 – Note the charge of the negative ion using the periodic table:

N has a charge of 3-

CONT’DStep #5 – (+) and (-) charges must balance.

Determine the charge on the metal ion that balances the negative ion:Since we know N has a charge of 3- the Au ion must have a charge of 1+ for it to balance the one N ion with a charge of 3-

Thus the name of the gold ion must be gold(I).

Step #6 - Write the name of the compound:gold (I) nitride

POLYATOMIC IONS An ion composed of more than one type of

atom joined by covalent bonds.

Carry an electric charge.

The suffix “ite” and “ate” are used to indicate the presence and number of oxygen atoms.

Rule “ate” polyatomic ions have one more oxygen than “ite” polyatomic ions.

Eg: PO43- : phosphate vs PO3

3-: phosphite

WRITING THE FORMULA FOR A POLYATOMIC ION

Write the formula for the following polyatomic ion: manganese (III) chlorate

Step #1- identify each ion and its charge:manganese (III): Mn3+

chlorate: ClO3- (refer to Table 4.11, pg 192)

Step #2-Balance charges:Mn3+ : = +3ClO3

- : -1 -1 -1 = - 3

Step #3 – Note ratio of positive to negative ions:1 Mn3+ : = +33 ClO3

- : -1 -1 -1 = - 3

CONT’D

Step #4 – Use brackets around ions to show ratio of ions:

(Mn)(ClO3)3

Step #5 – Omit brackets if the value outside the brackets is 1:

Mn(ClO3)3

NAMING COVALENT COMPOUNDS

Lets review what we know:

Ionic Compounds In ionic compounds subscripts are not used

to indicate the actual ratio of ions within a molecule but the smallest whole number ratio.

Covalent Compounds In covalent compounds subscripts are used

to show the precise actual number of atoms of each element in the molecule.

NAMING BINARY COVALENT COMPOUNDS

Binary Covalent Compound: contains 2 non-metals joined together by one or more covalent bonds.

Recall: atoms in covalent bonds do not bond by forming ions but rather share electrons.

Binary Covalent compounds can be made up of many atoms: C25H52 or can by diatomic: O2

NAMING COVALENT BONDS

Prefixes and their Meanings: Indicates the number of atoms present in

each element.

Prefixes are ONLY used for binary covalent compounds.

We will first begin by studying prefixes for naming compounds that do not contain H:- See Table 4.13 on pg. 194

FOR BINARY COMPOUNDS NOT CONTAINING H

RULES: #1. Prefix for the 1st element (+ ion) is only shown if it is present more than once: eg. CCl4

#2. Prefix “mono-” is shortened to “mon-” if placed before an oxide (- ion).

STEPS TO WRITING BINARY COVALENT COMPOUND NAMES

Eg - Write the name of: N2O3

Step #1- Name the element on the left first:nitrogen

Step #2 – Name the 2nd element: Oxygen becomes oxide (recall the “ide”

ending)

Step #3 – Add a prefix to each element:

dinitrogen trioxide

NAMES AND FORMULAS OF COVALENT COMPOUNDS

Covalent Compounds: both the name and chemical formula indicates the # or quantity of each type of atom.

For Example: dinitrogen trioxide OR

OR

N2O3

carbon disulfide CS2

REVIEW RULES FOR NAMING FORMULAS

Page 196