Lesson Notes By Weeks and Term v5 - Grade 8

Lesson Video

This page supports the lesson note with a companion video and a short classroom-ready summary.

For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.

Performance objectives

• Describe the basic structure of an atom (protons, neutrons, electrons).
• Define and use atomic number and mass number.
• Explain the arrangement of elements in the periodic table.
• Identify metals, non-metals, and metalloids and their properties.
• Define an ion and differentiate it from an atom.

Lesson summary

This week, we embark on a fascinating journey into the building blocks of matter: atoms! We will explore what atoms are made of, how they are organized, and how this organization dictates the properties of all the substances around us. Understanding atomic structure is crucial because it helps us understand why materials behave the way they do, from the strength of steel used in bridges to the way medicines interact with our bodies. It also explains why some elements are essential for life, like carbon and oxygen, while others can be harmful. The periodic table, a powerful tool, will be introduced as a way to organize and understand the elements.

Lesson notes

2.1 The Atom: The Basic Building Block All matter is made up of tiny particles called atoms. The word "atom" comes from the Greek word "atomos," meaning indivisible. While we now know that atoms are divisible, the name has stuck! An atom consists of three main subatomic particles: Protons: Positively charged particles found in the nucleus (the center) of the atom.

Neutrons: Neutrally charged (no charge) particles also found in the nucleus.

Electrons: Negatively charged particles that orbit the nucleus in specific energy levels or shells.

Think of it like the solar system: the nucleus is the sun, and the electrons are the planets orbiting around it. 2.2 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 and identifies the element. For example, all atoms with 6 protons are carbon atoms. We use 'Z' to represent the atomic number. You can find the atomic number of each element on the Periodic Table.

Mass Number (A): The total number of protons and neutrons in the nucleus of an atom. We use 'A' to represent the mass number. Mass Number (A) = Number of Protons + Number of Neutrons Therefore, Number of Neutrons = Mass Number (A) - Number of Protons (Z)

Example 1: Let's consider Sodium (Na). Its atomic number is 11, and its mass number is

2

3. Number of Protons = Atomic Number = 11 Number of Neutrons = Mass Number - Atomic Number = 23 - 11 = 12 Since atoms are neutral (equal positive and negative charges), Number of Electrons = Number of Protons = 11 Example 2: Consider Magnesium (Mg). Its atomic number is 12, and its mass number is

2

4. Number of Protons = Atomic Number = 12 Number of Neutrons = Mass Number - Atomic Number = 24 - 12 = 12 Number of Electrons = Number of Protons = 12 2.3 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. It’s a powerful tool that helps us predict how elements will behave.

Periods: The horizontal rows in the periodic table (numbered 1 to 7). Elements in the same period have the same number of electron shells.

Groups (or Families): The vertical columns in the periodic table (numbered 1 to 18). Elements in the same group have similar chemical properties because they have the same number of electrons in their outermost shell (valence electrons). 2.4 Metals, Non-metals, and Metalloids Elements can be broadly classified into three categories: Metals: Generally found on the left side of the periodic table. They are typically shiny, good conductors of heat and electricity, malleable (can be hammered into thin sheets), and ductile (can be drawn into wires).

Examples: Iron (Fe) used in building materials, Copper (Cu) used in electrical wiring, Gold (Au) used in jewellery.

Non-metals: Generally found on the right side of the periodic table. They are typically dull, poor conductors of heat and electricity, and brittle (easily broken).

Examples: Oxygen (O) which we breathe, Nitrogen (N) used in fertilizers, Carbon (C) the basis of all living things.

Metalloids (or Semi-metals): Found along the staircase line that separates metals from nonmetals. They have properties of both metals and non-metals. They are semiconductors, meaning they can conduct electricity under certain conditions.

Examples: Silicon (Si) used in computer chips, Germanium (Ge) also used in electronics. 2.5 Ions: Charged Atoms An ion is an atom that has gained or lost electrons, giving it an overall electrical charge.

Cation: A positively charged ion. Formed when an atom loses electrons. Metals often form cations. For example, Sodium (Na) can lose one electron to form a Sodium ion (Na+).

Anion: A negatively charged ion. Formed when an atom gains electrons. Non-metals often form anions. For example, Chlorine (Cl) can gain one electron to form a Chloride ion (Cl-).

Example 3: A Sodium atom (Na) has 11 protons and 11 electrons. If it loses one electron, it becomes a Sodium ion (Na+). Na+ ion: 11 protons, 10 electrons. The overall charge is +1 (11 positive charges - 10 negative charges = +1). 2.6 Molecules and Chemical Formulas A molecule is formed when two or more atoms are held together by chemical bonds. A chemical formula uses symbols and numbers to represent the types and number of atoms in a molecule.

Water (H2O): Two hydrogen atoms (H) and one oxygen atom (O) bonded together.

Carbon Dioxide (CO2): One carbon atom (C) and two oxygen atoms (O) bonded together.

Methane (CH4): One carbon atom (C) and four hydrogen atoms (H) bonded together. We can represent molecules using diagrams. For example, water (H2O) can be represented as: O-H-H (where the lines represent the chemical bonds). Guided Practice (With Solutions)

Question 1: An atom has an atomic number of 8 and a mass number of

1

6. How many protons, neutrons, and electrons does it have? What element is it?