Multivalent Species

• Ions of a certain elements can have more than one possible charge. Such elements are called multivalent species.

• For example, copper is multivalent - its ions can have either a 1+ or a 2+ ion charge (Cu + or Cu 2+).

• You use a Roman numeral in the cation name to indicate its charge. – CuCl2 is named copper(II) chloride. (copper is

in the Cu2+ form.)   – CuCl is named copper(I) chloride.  (the copper

is in the  Cu+ form.)

Chemical Formulas Involving Multivalent Species:

• Writing formula units from names which include multivalent species uses the same approach you learned for other binary ionic compounds.  The only difference is you have to indicate the charge of the multivalent species with roman numerals.

• Only use roman numerals for metals that have more than one charge! 

• For instance silver only has one possible charge (Ag+) so do not use roman numerals.

• Write the chemical formula for iron(II) chloride.

1. Write down the symbols of the ions involved – Iron (II) (the roman numeral tells us it has a 2+ charge)

Fe2+– Chloride (group 17 thus has a 1- charge)  Cl -

2. Determine the lowest whole number ratio of ions that will give a net charge of zero.

– (Fe2+) x 1 = 2+          (Cl -) x 2 = 2-–                 (2+)  +  (2 -) = 0 net charge 

3. Write the formula removing all charges. • FeCl2

• Your turn:• Write chemical formulas for the following

compounds:• 1.  Titanium (III) fluoride • 2.  Titanium (IV) fluoride • 3.  Nickel (II) oxide • 4.  Lead (IV) sulfide • 5.  Vandium(V) oxide•  

• Rules For writing Formulas for multivalent Binary Ionic Compounds

1. Determine if the metal has more than one possible charge (multivalent).

o consult periodic table

2. Determine charge of anion. (Anions only have one possible charge).

o recall group number

3. Pick the metal ion that results in a net charge of zero.

4. Write the name of the compound be sure to indicate the identity of the metal ion with Roman Numerals.

Write the IUPAC name for SnCl4. 1.  Determine if the metal has more than one possible charge

(multivalent).– ·Sn  has two possible charges Sn4+ and Sn2+ . 

» We have to decide which charge we have.

2.  Determine charge of anion. (Anions only have one possible charge).

– ·         The chloride ion has a 1- charge because chlorine is a Group 17 element. (Cl can only have one charge 1-)

3.  Pick the metal ion that results in a net charge of zero.» Since there are four chloride ions in the formula, the charge on tin ions

must be 4+. » (Cl 1-) x 4 = 4 -

» (Sn X+) x 1 = 4+– Sn4+

4.  Write the name of the compound be sure to indicate the identity of the metal ion with Roman Numerals.

•  SnCl4 is tin (IV) chloride.

• Your Turn:• Write the names for the following compounds:• 1.  CrBr3 • 2.  TiO2   • 3.  AuCl3 • 4.  Fe2O3 • 5.  AgI

 

5.9 Polyatomic Compounds Some compounds like calcium carbonate and copper (II) sulphate do not end in “ide” like other ionic compounds. Why? Such compounds are pure substances that involve a metal ion and a polyatomic or complex ion. Polyatomic ions are groups of atoms that tend to stay together and carry an overall charge. E.g. sulphate ion is SO4

-2

Writing Formulas for Polyatomic Compounds

We use the same steps that we learned in section 5.8

 What is the formula for copper (II) sulphate 1)      write the symbols for the metal and the polyatomic group

Cu SO4

2)     write the ionic charges +2 -2

Cu SO4

 3)     Criss Cross and reduce the subscripts to their simplest terms if possible. (Brackets) may be needed if there is 2 or more polyatomic ions. Never change the subscript of the polyatomic group. 

Cu2 SO42 = Cu2 (SO4)2

= Cu SO4

Naming Polyatomic Compounds The name of the above compound is Copper (II) Sulphate The name is simply the name of the metal (use a roman numeral if the metal has more than 1 positive charge) and the name of the polyatomic ion . Both can be found on the periodic table by looking them up.

Oxyacids Oxyacids are compounds formed when hydrogen (H +1) combines with polyatomic groups that contain oxygen 

E.g. HNO3 is nitric acid 

H +1 NO3 –1 = HNO3 

Use the acid naming table on the back of your periodic table to name and

write the formulas of all ionic compounds that begin with hydrogen

Hydrogen _______ide becomes hydro_________ic acidHydrogen _______ate becomes _____________ic acidHydrogen _______ite becomes ____________ous acid

chlor chlor

chlor chlor

chlor chlor

Assignment• U3 S2 L7 – Worksheet 1

• A2-A7

• Homework : Q 1-7 pg 198