Ch. 2.3: Formulae and Equations

Question 1

Describe the trend for ionisation across the groups of the periodic table.

Answer 1

Group : 1 2 3 4 5 6 7 8

Charge: + 1 , + 2, +3, 0, -3, -2, -1 , 0

Question 2

Give some examples of ions that can have different charges.

Answer 2

Iron (ii) = Fe2+
Iron (iii) = Fe3+

Copper (i) = Cu+
Copper (ii) = Cu2+

Question 3

What is a binary compound? How do you name one?

Answer 3

Binary compound: only contains two elements.

To name it, you use the first name of the first element, but change the ending of the second elements name to -ide.

For ionic compounds the metal ion always comes first.

Question 4

Define polyatomic ion

Answer 4

An ions that contains atoms of more than one element bonded together.

Question 5

What is the symbol for the following polyatomic ions : ammonium, hydroxide, nitrate, nitrite, hydrogencarbonate, manganate (vii) (permanganate , carbonate, sulfate, sulfite, dichromate, phosphate

Answer 5

ammonium - (NH4)+
Hydroxide - OH- 
Nitrate - (NO3)-
Nitrite - (NO2)-
Hydrogencarbonate - (HCO3)- 
Manganate - (MnO4)- 
Carbonate - (CO3)2-
Sulfate - (SO4)2-
Sulfite - (SO3)2-
Dichromate - (Cr2O7) 2-
Phosphate -( PO4)3-

Question 6

How do you know you have written the correct formula for an ionic compound?

Answer 6

• the overall charge is zero as the ionic charges balance
• sum of positive charges = sum of negative charges

Trick : it often works to just swap the charges and put them in subscript.

E.g. Zn2+ and Cl- = ZnCl2
Al3- , (SO4)2- = Al2(SO4)3

Question 7

What are the diatomic molecules? What is the molecule that comes in fours?

Answer 7

H2 N2 O2 F2 Cl2 Br2 I2

Phosphorus = P4

Question 8

What are the four different state symbols

Answer 8

( g ) = gas
( l ) = liquid
( s ) = solid
( aq ) = aqueous ( dissolved in water )