Matter and Its Properties · SHS1 Chemistry

Lesson notes

Learning Objectives

Indicator: 1.1.1.LI.1 - Explain relative atomic mass and relative molecular mass.

By the end of the lesson, learners can:

Define relative atomic mass (Ar) as the average mass of atoms of an element compared to one-twelfth the mass of one atom of carbon-12, using the standard scale.
Define relative molecular mass (Mr) as the sum of the relative atomic masses of all atoms in a molecule or formula unit of a substance.
Calculate the relative atomic mass of an element from the masses and relative abundances of its isotopes.
Calculate the relative molecular mass of a compound given its chemical formula and the relative atomic masses of its constituent elements.
Explain why the carbon-12 isotope is the standard reference scale for measuring atomic and molecular masses.

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Curriculum details

Strand: Physical Chemistry (Strand 1)
Sub-strand: Matter and Its Properties (1.1)
Content standard: 1.1.1.CS.2 - Demonstrate an understanding of the mole concept and its significance to the quantitative analysis of chemical reaction. 1.1.1.LO.1 Use the knowledge and understanding of the scientific practices in Chemistry to explain the structure of the atom as well as the stability of its nucleus. 1.1.1.LO.2 Use the mole concept to determine the amount and quantity of various substances involved in chemical reactions. 1.1.1.LO.3 Write mole ratios for chemical equations and apply it in quantitative analysis. 1.1.1.LO.4 Use the kinetic theory of matter to explain the behaviour of solids, liquids and gases under different conditions and describe the laboratory preparation of gases as well as their uses in everyday life.
Indicator: 1.1.1.LI.1 - Explain relative atomic mass and relative molecular mass.
Suggested placement: Semester 1, Week 11 (Week 11 of the year)
Our suggestion, laid out in curriculum order across three terms of twelve weeks. NaCCA does not fix the week, so follow your school's scheme of learning.
Curriculum reference: NaCCA curriculum document, p. 34

Exemplars (from the NaCCA curriculum)

Prior to the lesson: Find-out why carbon-12 isotope is used as a reference scale for measurement.
Activity-Based learning: Use a beam balance to demonstrate the determination of the mass of an element/compound by placing the standard (Carbon-12) in one pan and the mass to be determined in the other pan.
Teaching and Learning Materials:
- * Worksheets with sample questions * Worksheets to record results. * Na CO 2 3 * CaCl 2 * Bolt and nuts * Resources for measuring volume and preparing solutions * Weighing scale
- * Calculator
- * Periodic table containing the elements with their relative atomic masses * Calculator * Beam balance or diagram of beam balance Substances of different weights
- * Apparatus (beaker, flask, weighing * Worksheet on the of substance and molar * Solid solutes
- Liquid solutes (e.g., water)
- CHARTS * Charts between other quantities
- for preparing solutions funnel, stirrer, volumetric scale), with sample questions interconversion of amount to number of entities quantities. (e.g., NaOH, NaCl) (e.g., HCl) Solvent
- showing interconversion amount of substance and
Assessment (1.1.1.AS.1). The document marks these depth-of-knowledge levels for this indicator: Level 2 Skills of conceptual understanding.