# Lesson Notes By Weeks and Term - Senior Secondary 1

Particulate nature of matter III

Term: 1st Term

Week: 10

Class: Senior Secondary School 1

Age: 15 years

Duration: 40 minutes of 5 periods each

Date:

Subject:      Chemistry

Topic:-       Particulate nature of matter III

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to

1. Explain atomic number, mass number and isotopy
2. Calculate the relative atomic masses based on C4 isotope

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers, demonstration, videos from source

INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures

INSTRUCTIONAL PROCEDURES

PERIOD 1-2

 PRESENTATION TEACHER’S ACTIVITY STUDENT’S ACTIVITY STEP 1 INTRODUCTION The teacher reviews the previous lesson on particulate nature of matter Students pay attention STEP 2 EXPLANATION He explains atomic number, mass number and isotopy Students pay attention and participates STEP 3 DEMONSTRATION He shows the learners how to calculate the relative atomic masses and relative molecular mass based on C4 isotopes Students pay attention and participate STEP 4 NOTE TAKING The teacher writes a summarized note on the board The students copy the note in their books

NOTE

PARTICULATE NATURE OF MATTER

ATOMIC OR PROTON NUMBER

This is the number of protons in an atom. The atomic number is represented by the symbol z. in a neutral atom, the number of protons equals the number of electrons (p=e)

MASS OR NUCLEON NUMBER

This is the sum of protons and neutrons in an atom. It is represented by the letter A (A= p + n)

Proton and neutron has 1 unit each and are concentrated at the centre in the nucleus of the atom, with electron around the shell. Atomic number is used to arrange the electron on the shell while the number of proton and neutron determines the weight of the atom.

From Dalton’s theory it is possible for atoms to have different number of neutron, hence different mass number. For neutral atom, the number of proton and the electron is the same.

ISOTOPES AND ISOTOPY

Isotopes are atoms of the same element having the same atomic number but different mass number. This is due to the number of neutron they contain

Isotopy is a phenomenon or the ability of an atom of the same element to have different mass number.

Isotopes have the same chemical properties since they have same number of electrons but their physical properties are different because of different number of neutron.

Relative atomic mass of element (Ar)

With the existence of isotopy in elements there arose the need to measure the mass of element in relative term with the view to obtain the average mass of respective elements. Relative atomic mass could be obtained using carbon -12 scales.

Relative molecular mass (Mr)

This is the sum of the relative atomic masses of elements that makes up the molecules of the substance or compound

Example ( Ar Cl=35.5, H=1, Na=23, S=32, O=16,C=12, Ca=40, Mg=24)

Mr      for NaCl = Ar Na + Ar Cl

= 23+35.5 = 58.8 g/mol.

Mr  for MgSO4 = Mg + S +4O

=24 +32+ (4x16) =120 g/mol.

Mr  for Ca(HCO3)2=Ca + 2H + 2C+ 6O

= 40 +(2x1) + (2x12) +( 6x16)

= 40+2+24+96

= 162 g/mol.

Note Mr  & Ar have no unit

EVALUATION:    1. Explain briefly

1. atomic number
2. mass number

2. Define Isotopes and Isotopy

3. Give two examples of common isotopes

4. Calculate the relative molecular mass of

1. H2SO4
2. Al2O3
3. Ca(NO3)2
4. (NH4)2SO4

( Ar Cl=35.5, H=1, Na=23, S=32, O=16,C=12, Ca=40, Al=27 N=14                             Mg=24)

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively