1. STOICHIOMETRIC RELATIONS
The Mole Concept

2. The mole concept Avogadro’s Number (L)= 6.02214129*1023
1 mole substance contains the particles as the amount of Avogadro’s number.
Avogadro’s Number (L)= *1023

3. Number of Particles (N) = Mole number (n) * Avogadro constant (L)
The mole concept
Number of moles: n Number of particles: N
Number of Particles (N) = Mole number (n) * Avogadro constant (L)
WE 1, Exercises 13, Test yourself pg 12

4. The mass of an individual atom in a sample of an element is taken as a weighted average of its different (isotope) masses.
𝑨 𝒓 = 𝑾𝒆𝒊𝒈𝒉𝒕𝒆𝒅 𝒂𝒗𝒆𝒓𝒂𝒈𝒆 𝒐𝒇 𝒐𝒏𝒆 𝒂𝒕𝒐𝒎 𝒐𝒇 𝒕𝒉𝒆 𝒆𝒍𝒆𝒎𝒆𝒏𝒕 𝟏 𝟏𝟐 𝒎𝒂𝒔𝒔 𝒐𝒇 𝒐𝒏𝒆 𝒂𝒕𝒐𝒎 𝒐𝒇 𝑪−𝟏𝟐
Has no unit

5. Relatıve atomıc mass
Mass spectrometer is an instrument to measure the mass of individual atoms.
The mass of a H atom = 1.67*10-24 g
The mass of a C atom = 1.99*10-23 g
C/H = 11.9 ≈12
The mass needs to be recorded relative to some agreed standard.
As C is a very common element which is easy to transport and store because it is a solid.
The mass of standard 12C isotope is 12, but relative atomic mass of C element is , because 12C has 13C and 14C isotopes.

6. Relatıve average mass
The mass spectrum of Zirconium is shown as below: So, calculate the relative average mass of Zirconum.
51.5
11.2
17.1
17.4
2.8

7. Relatıve average mass
Chlorine has 2 isotopes as 𝟑𝟓 𝑪𝒍 and 𝟑𝟕 𝑪𝒍 . If the abundance of 𝟑𝟓 𝑪𝒍 is %75, what is the average weight of chlorine?
Average = = 35.5
is also relative atomic mass of chlorine

8. Relatıve Formula mass; 𝑀 𝑟
The mass of a compound (or molecular element) calculated by the relative atomic masses of its atoms: (No unit again) For example: H2 = 2*1.01 =2.02 H2O = 2* = 18.02
Test yourself pg 9

9. MOLAR MASS; M The mass of 1 mole substance. Has unit g.mol-1
For example:
H2 = 2*1.01 =2.02 g.mol-1
H2O = 2* = g.mol-1
Exercises 16 – 23
Test yourself pg 11

10. Empırıcal formula of a compound
The formula which is the simplest whole-number ratio of the elements in a compound.
For example:
The empirical formula of C6H6 is CH.
WE 2, 3, 4, Exercises 24, 25, 26, 27, 34
TY q.13, 16, 17, 18, 19

11. molecular formula of a compound
The formula which shows all atoms present in a molecule of a compound.
For example:
C6H6 is the molecular formula of benzene.
WE 6, 7, Exercises 31, 32, 33, TY q.14, 15

12. Percentage composıtıon by mass
Let’s see CaCO3 (Ar; Ca: C:12.01 O: 16.00) %Ca = = %C = = %O = =15.98
Exercises 28, 30, TY pg 14

13. QUIZ SL & HL Questions on the mole and Avogadro’s constant
SL & HL Questions on Empirical and molecular formulas