Lesson Notes By Weeks and Term v5 - Grade 8

Lesson Video

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Performance objectives

• Identify the three subatomic particles.
• Draw simple diagrams of the first 20 elements.
• Explain the structure of the Periodic Table.
• Use atomic and mass numbers to find protons, neutrons, and electrons.

Lesson summary

Welcome, Grade 8 Natural Sciences learners! This week, we're diving into the fascinating world of atoms and the Periodic Table. Understanding atoms is crucial because everything around us – from the air we breathe to the soil that grows our food, to the gadgets we love – is made of them. The Periodic Table is like a map of all known elements, organizing them in a way that reveals their properties and how they interact. Understanding atomic structure and the periodic table allows us to predict and understand chemical reactions that are essential for life and industry.

Lesson notes

2. 1.

The Atom: The Building Block of Matter Everything around us is made of matter, and the smallest unit of matter that retains the chemical properties of an element is called an atom. Atoms are incredibly tiny – you can't see them with the naked eye! They are made up of even smaller particles called subatomic particles. 2.

2. Subatomic Particles: There are three main types of subatomic particles: Protons: These have a positive (+) charge and are located in the nucleus (the center) of the atom. The number of protons determines what element the atom is. For example, all atoms with one proton are hydrogen atoms, all atoms with six protons are carbon atoms, and so on.

Neutrons: These have no charge (they are neutral) and are also located in the nucleus of the atom. Neutrons contribute to the mass of the atom but don't affect its charge.

Electrons: These have a negative (-) charge and orbit the nucleus in specific energy levels called electron shells. The electrons are much lighter than protons and neutrons.

Summary Table: | Subatomic Particle | Charge | Location | Relative Mass | | :----------------- | :----- | :---------- | :------------ | | Proton | +1 | Nucleus | 1 | | Neutron | 0 | Nucleus | 1 | | Electron | -1 | Electron Shells | Almost 0 | 2.

3. Atomic Number and Mass Number: Atomic Number (Z): This is the number of protons in the nucleus of an atom. It's like the atom's identity card. Elements are arranged in the Periodic Table in order of increasing atomic number.

Mass Number (A): This is the total number of protons and neutrons in the nucleus of an atom.

Number of Neutrons: You can calculate the number of neutrons by subtracting the atomic number from the mass number: Number of Neutrons = Mass Number (A) - Atomic Number (Z) 2.

4. Electron Shells (Energy Levels): Electrons don't just randomly orbit the nucleus; they are arranged in specific energy levels or shells. These shells have a maximum number of electrons they can hold: First shell (closest to the nucleus): Maximum of 2 electrons Second shell: Maximum of 8 electrons Third shell: Maximum of 8 electrons (for the elements we're studying now) To fill up the shells, electrons start filling from the innermost shell outwards. 2.

5. The Periodic Table: The Periodic Table is a chart that organizes all the known elements in order of increasing atomic number. Elements with similar chemical properties are grouped together in columns called groups (vertical) and rows called periods (horizontal). The Periodic Table is organized as follows: Periods: Rows represent the number of electron shells an atom of that element has.

Groups: Columns represent the number of valence electrons (electrons in the outermost shell). Elements in the same group have similar chemical properties because they have the same number of valence electrons. 2.

6. Worked

Examples: Example 1: Oxygen (O) Atomic Number (Z) = 8 Mass Number (A) = 16 Number of Protons = Atomic Number = 8 Number of Electrons = Number of Protons = 8 (for a neutral atom) Number of Neutrons = Mass Number - Atomic Number = 16 - 8 = 8 Electron Configuration: 2 electrons in the first shell, 6 electrons in the second shell (2, 6)

Example 2: Sodium (Na) Atomic Number (Z) = 11 Mass Number (A) = 23 Number of Protons = Atomic Number = 11 Number of Electrons = Number of Protons = 11 (for a neutral atom) Number of Neutrons = Mass Number - Atomic Number = 23 - 11 = 12 Electron Configuration: 2 electrons in the first shell, 8 electrons in the second shell, 1 electron in the third shell (2, 8, 1)

Example 3: Calcium (Ca) Atomic Number (Z) = 20 Mass Number (A) = 40 Number of Protons = Atomic Number = 20 Number of Electrons = Number of Protons = 20 (for a neutral atom) Number of Neutrons = Mass Number - Atomic Number = 40 - 20 = 20 Electron Configuration: 2 electrons in the first shell, 8 electrons in the second shell, 8 electrons in the third shell, 2 electrons in the fourth shell (2, 8, 8, 2) 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) How many electrons does it have (assuming it is neutral)?

Solution: a) Atomic number = Number of protons = 17 b) Mass number = Number of protons + Number of neutrons = 17 + 18 = 35 c) Number of electrons = Number of protons = 17 (since it's a neutral atom)

Question 2: Draw a diagram of a Boron atom (B), which has an atomic number of 5 and a mass number of

1

1. Show the protons and neutrons in the nucleus, and the electrons in their shells.

Solution: Protons = Atomic number = 5 Neutrons = Mass number - Atomic number = 11 - 5 = 6 Electrons = Number of protons = 5 Diagram: (Imagine a drawing here that you would do on a whiteboard)

Nucleus: 5 protons and 6 neutrons First shell: 2 electrons Second shell: 3 electrons Question 3: An element 'X' has an electron configuration of (2, 8, 2). a) In which group of the periodic table is it? b) In which period of the periodic table is it?