CHAPTER 3: CHEMICAL FORMULAE & EQUATIONS

4S1Monday, 7/2/201110.45 – 11.55 am

Thermochemistry

Salts

Acids &

Bases

Periodic Table of Element

s

ElectrochemistryOxidation & Reduction

Rate of Reaction

CHEMICAL FORMULAE AND

EQUATIONS

A. Relative Atomic Mass & Relative Molecular Mass

B. The Mole and the Number of Particles

C. The Mole and the Mass of Substances

D. The Mole and the Volume of Gas

E. Chemical FormulaeF. Chemical Equations

What is the mass of an atom?Since an atom is very small, there is no machine in the world that can weigh it.Therefore, to determine the mass of an atom, scientists compare the mass of one atom of the element to the mass of one atom of carbon-12

Relative Atomic Mass (RAM) of an

element???Average mass of one atom of the element when

compared with 1/12 of the mass of an atom of carbon-12

Relative Atomic Mass (RAM) of an

element???= The average mass of one atom of the

element1/12 x the mass of an atom of carbon-

12

Relative Molecular Mass (RMM) of a molecule???

Average mass the molecule when compared with 1/12 of

the mass of an atom of carbon-12

Relative Molecular Mass (RMM) of a molecule???

= The average mass of the molecule

1/12 x the mass of an atom of carbon-12

Why do we compare with carbon-12?(why is carbon-12 used as standard?)•It is solid•It is easily handled•It is used as a reference standard in the mass spectrometer

Refer page 28 of

your Textbook

Calculating RMM of a molecule

= add up the RAM of all

atoms present in the molecule

Refer page 176 of your

Textbook

Example 1:Calculate the RMM of H2

RMM of H2 = RAM of H + RAM of H

= 2 x (RAM of H)

= 2 x 1 = 2

Example 2:Calculate the RMM of N2

RMM of N2 = RAM of N + RAM of N

= 2 x (RAM of N)

= 2 x 14 = 28

Example 3:Calculate the RMM of NaOH

RMM of NaOH = RAM of Na + RAM of O + RAM of H= 23 + 16 + 1= 40

REMINDER !!!RAM & RMM is a number without unit

HOMEWORK:Exercise book:

Try This Out 3.1 page 17 of Practical

TextbookSubmit: Thursday, 10/2/11