# 3 Isotopes and Mass calculations Objectives Defining and

3. Isotopes and Mass calculations Objectives: Defining and calculating Ar and Mr for ionic and molecular substances

Relative atomic mass Calculations 1. What is relative atomic mass calculated from? 2. Why is it rarely a whole number? 3. Find the Ar of the following: Caesium Cadmium Copper 4. How is Ar different from Relative Isotopic mass?

The periodic table states that the Relative Atomic Mass (Ar) of Boron is 11 Boron has two naturally occurring isotopes. 80% of all Boron is B 11 (6 neutrons) 20% of all Boron is B 10 (5 Neutrons) Calculate the average relative atomic mass of Boron. (80 x 11) + (20 x 10) = 100 10. 8

The periodic table states that the Relative Atomic Mass (Ar) of Copper is 64 Copper has two naturally occurring isotopes. 69% of all Copper is Cu 63 (34 neutrons) 31% of all Copper is Cu 65 (36 Neutrons) Calculate the average relative atomic mass of Boron. (69 x 63) + (31 x 65) = 100 63. 6

The periodic table states that the Relative Atomic Mass (Ar) of Magnesium is 24 Magnesium has three naturally occurring isotopes. 79% of all Magnesium is Mg 24 (12 neutrons) 11% of all Magnesium is Mg 25 (13 Neutrons) 10% of all Magnesium is Mg 26 (14 neutrons) Calculate the average relative atomic mass of Magnesium. (79 x 24) + (11 x 25) + (10 x 26) = 100 24. 3

Relative molecular mass Calculations 1. Write the definition for this 2. How do you calculate Mr? 3. Find the relative molecular mass of the following compounds: NH 4 CO 2 C 6 H 12 O 6

Relative formula mass Calculations 1. Write the definition for this 2. How id this different to Relative Molecular mass? 3. How do you calculate Relative formula mass? 4. Find the relative molecular mass of the following compounds: Ca. F 2 Si. O 2 Na. OH

- Slides: 7