Lesson Notes By Weeks and Term v5 - Grade 8

Lesson Video

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Performance objectives

• Define atom, element, proton, neutron, and electron.
• Draw simple diagrams of the first 20 elements.
• Explain how proton number defines an element.
• Describe the organization of the Periodic Table.
• Identify metals, non-metals, and metalloids.

Lesson summary

This week, we delve into the fascinating world of atoms and how they're organized in the Periodic Table. Understanding atomic structure is fundamental to comprehending everything around us, from the air we breathe to the materials used in building our homes and schools. Almost every material we use in our daily lives, from the plastics in our cellphones to the metals in our pots, is made of atoms. Understanding how these atoms interact will help us to understand the properties of the materials. This knowledge is crucial for fields like medicine, engineering, and environmental science, all of which are vital to South Africa's development and progress.

Lesson notes

2. 1. What is Matter Made Of? Everything around us – solids, liquids, and gases – is made up of matter. Matter is anything that has mass and takes up space (volume). The fundamental building block of matter is the atom. 2.

2. The Atom: A Closer Look An atom is the smallest unit of an element that retains the chemical properties of that element.

Think of it like this: if you break down a gold nugget into smaller and smaller pieces, you eventually reach a point where you have a single gold atom. If you break it down further, it no longer behaves like gold. Atoms are made of even smaller particles, called subatomic particles: Protons: Positively charged particles found in the nucleus (the center) of the atom. The number of protons determines what element the atom is.

Neutrons: Neutrally charged (no charge) particles also found in the nucleus. Neutrons contribute to the mass of the atom but do not affect its charge.

Electrons: Negatively charged particles that orbit the nucleus in specific energy levels or shells. Electrons are much lighter than protons and neutrons.

Analogy: Imagine an atom as a soccer stadium. The nucleus is like the center circle, where the protons and neutrons (the players) are located. The electrons are like fans moving around the stadium (nucleus) in the stands (energy levels). 2.

3. Atomic Number and Mass Number Atomic Number (Z): The number of protons in the nucleus of an atom. This number is unique to each element. For example, all hydrogen atoms have 1 proton (Z=1), and all carbon atoms have 6 protons (Z=6). You can find the atomic number of an element on the Periodic Table.

Mass Number (A): The total number of protons and neutrons in the nucleus of an atom. To calculate the number of neutrons, we can use the formula: Number of neutrons = Mass Number (A) - Atomic Number (Z) The mass number is not usually found on the periodic table because most elements exist as different isotopes (atoms with the same number of protons but a different number of neutrons). The relative atomic mass on the periodic table is an average based on the abundance of these isotopes.

Example 1: Carbon (C) Carbon has an atomic number of 6 (Z=6) and a mass number of 12 (A=12). Number of protons = 6 Number of electrons = 6 (in a neutral atom, the number of protons equals the number of electrons) Number of neutrons = A - Z = 12 - 6 = 6 Example 2: Sodium (Na) Sodium has an atomic number of 11 (Z=11) and a mass number of 23 (A=23). Number of protons = 11 Number of electrons = 11 Number of neutrons = A - Z = 23 - 11 = 12 2.

4. Electron Arrangement (Electron Configuration) Electrons don't just float around randomly. They occupy specific energy levels or shells around the nucleus. The first shell (closest to the nucleus) can hold a maximum of 2 electrons. The second shell can hold a maximum of 8 electrons. The third shell can hold a maximum of 8 electrons (up to element 20 – Calcium). To determine the electron arrangement, we simply fill the shells starting from the innermost shell.

Example 3: Oxygen (O) (Atomic Number = 8) Oxygen has 8 electrons.

First shell: 2 electrons Second shell: 6 electrons Electron arrangement: 2.6 Example 4: Magnesium (Mg) (Atomic Number = 12) Magnesium has 12 electrons.

First shell: 2 electrons Second shell: 8 electrons Third shell: 2 electrons Electron arrangement: 2.8.2 2.

5. The Periodic Table: Organizing the Elements The Periodic Table is a chart that organizes all known elements based on their atomic number and chemical properties. Elements with similar properties are grouped together.

Periods: Horizontal rows in the Periodic Table. The period number corresponds to the highest energy level (shell) occupied by electrons in that element.

Groups: Vertical columns in the Periodic Table. Elements in the same group have similar chemical properties because they have the same number of electrons in their outermost shell (valence electrons). 2.

6. Metals, Non-metals, and Metalloids Elements can be classified into three main categories based on their properties: Metals: Generally shiny, good conductors of heat and electricity, malleable (can be hammered into shapes), and ductile (can be drawn into wires). Most elements are metals.

Examples: Iron (Fe), Copper (Cu), Gold (Au). Metals are found on the left side of the periodic table.

Non-metals: Generally dull, poor conductors of heat and electricity, and brittle (easily broken).

Examples: Oxygen (O), Sulfur (S), Carbon (C). Non-metals are found on the right side of the periodic table.

Metalloids (Semi-metals): Have properties of both metals and non-metals. They are semiconductors, meaning they conduct electricity under certain conditions. This makes them useful in electronics.

Examples: Silicon (Si), Germanium (Ge). Metalloids are found along the staircase line separating metals and nonmetals. Guided Practice (With Solutions)

Question 1: An atom has 17 protons and 18 neutrons. a) What is its atomic number? b) What is its mass number? c) What element is it?