Lesson Notes By Weeks and Term v5 - Grade 8

Lesson Video

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Performance objectives

• Define atom, element, proton, neutron, and electron.
• Find the number of protons, neutrons, and electrons for the first 20 elements.
• Describe the arrangement of the Periodic Table (groups and periods).
• Explain the difference between metals and non-metals.

Lesson summary

Hello Grade 8 Natural Sciences learners! This week, we're diving into the fascinating world of atoms and how they're organized on the Periodic Table. Understanding atoms is crucial because everything around us is made of them! From the air we breathe to the food we eat, and even the soil our plants grow in, it's all atoms. In South Africa, understanding these concepts helps us understand the composition of our natural resources like the minerals mined in our country, how different materials react, and even helps to inform solutions for issues like water purification. Think about gold mining in Gauteng – it all starts with understanding the atomic structure and properties of gold.

Lesson notes

2.1 The Atom: Building Block of Matter Everything around us is made up of matter. And matter is made up of tiny particles called atoms. An atom is the smallest unit of an element that retains the chemical properties of that element. Imagine breaking down a piece of gold into smaller and smaller pieces. Eventually, you'll reach a point where you can't break it down anymore without changing its properties. That's an atom of gold. Atoms themselves are made up of even smaller particles called subatomic particles: Protons: Positively charged particles located in the nucleus (the center) of the atom. The number of protons determines what element the atom is. Think of it like a fingerprint - each element has a unique number of protons. This number is called the atomic number.

Neutrons: Neutrally charged (no charge) particles also located in the nucleus. Neutrons contribute to the mass of the atom but don't affect its charge.

Electrons: Negatively charged particles that orbit the nucleus in specific energy levels or shells. Electrons are much smaller than protons and neutrons. They are involved in chemical reactions, determining how atoms interact with each other.

Analogy: Think of an atom like a small soccer stadium. The nucleus, containing protons and neutrons, is like the center circle. The electrons are like the fans, orbiting around the circle in the stands (energy levels). 2.2 Elements and the Periodic Table An element is a pure substance that consists only of atoms that have the same number of protons. For example, all atoms of gold have 79 protons. The Periodic Table of Elements is a chart that organizes all known elements based on their atomic number (number of protons) and their chemical properties.

Key Features of the Periodic Table: Atomic Number: This is the number of protons in an atom of that element. It's usually found at the top of each element's box on the periodic table.

Symbol: A one- or two-letter abbreviation for the element's name (e.g., H for Hydrogen, O for Oxygen, Au for Gold (from the Latin aurum)).

Name: The element's name (e.g., Hydrogen, Oxygen, Gold).

Mass Number (Atomic Mass): This is approximately the total number of protons and neutrons in an atom of that element. It's usually found at the bottom of each element's box. It's important to note this is usually a decimal number, representing the average atomic mass of different isotopes of that element (we'll explore isotopes later, but for now, treat it as a guide to the number of protons + neutrons). To estimate the number of neutrons, subtract the atomic number (number of protons) from the mass number.

Organisation of the Periodic Table: Periods: The horizontal rows are called periods. Elements in the same period have the same number of electron shells. The period number indicates the number of electron shells.

Groups (or Families): The vertical columns are called groups or families. Elements in the same group have similar chemical properties because they have the same number of electrons in their outermost shell (valence electrons).

Example: Finding Information on the Periodic Table Let’s look at Sodium (Na): Atomic Number (top number): 11 (Therefore, Sodium has 11 protons)

Symbol: Na Name: Sodium Mass Number (bottom number): Approximately

2

3. We can estimate it has roughly 23 - 11 = 12 neutrons. 2.3 Calculating Number of Neutrons Number of Neutrons = Mass Number – Atomic Number Example 1: Calculate the number of neutrons in an atom of carbon (C). Carbon has an atomic number of 6 and a mass number of approximately

1

2. Number of Neutrons = 12 - 6 = 6 neutrons Example 2: Calculate the number of neutrons in an atom of Iron (Fe). Iron has an atomic number of 26 and a mass number of approximately

5

6. Number of Neutrons = 56 – 26 = 30 neutrons Important

Note: In a neutral atom (an atom with no overall charge), the number of electrons is equal to the number of protons. This is because the positive charge of the protons cancels out the negative charge of the electrons. So, Sodium has 11 protons and 11 electrons. 2.4 Metals and Non-metals The Periodic Table can be divided into two main categories: metals and non-metals.

Metals: Generally found on the left side of the Periodic Table.

Physical properties: Lustrous (shiny): They reflect light well (think of silverware or gold jewelry).

Good conductors of heat and electricity: This is why metal pots are used for cooking and copper wires are used in electrical circuits.

Malleable: They can be hammered into thin sheets (like aluminum foil).

Ductile: They can be drawn into wires (like copper wires). Solid at room temperature (except for mercury, which is a liquid).

Examples: Iron (Fe), Copper (Cu), Gold (Au), Aluminum (Al)

Non-metals: Generally found on the right side of the Periodic Table.

Physical properties: Dull (not shiny): They don't reflect light well.

Poor conductors of heat and electricity: They are often used as insulators.

Brittle: They break easily when hammered or bent.