Lesson Notes By Weeks and Term v5 - Grade 8

Lesson Video

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Performance objectives

• Define the structure of an atom (protons, neutrons, electrons).
• Explain atomic number and identify elements on the Periodic Table.
• Relate element arrangement to electron configurations.
• Define 'group' and 'period' on the Periodic Table.
• Distinguish between metals, non-metals, and metalloids.

Lesson summary

This week, we delve deeper into the fascinating world of atoms and how they are organized in the Periodic Table. Understanding atomic structure is crucial for understanding everything around us, from the air we breathe (oxygen and nitrogen) to the water we drink (hydrogen and oxygen) and the materials that make up our homes and schools. In South Africa, understanding the properties of elements is important in many industries, including mining (gold, platinum), agriculture (fertilizers), and medicine (pharmaceuticals). For example, knowing the properties of different metals helps engineers choose the right material to build strong and safe bridges or buildings.

Lesson notes

2. 1. The Structure of the Atom Atoms are the basic building blocks of all matter. Each atom consists of a central nucleus surrounded by orbiting electrons.

Protons: These are positively charged particles located in the nucleus. The number of protons determines what element an atom is. For example, all atoms with one proton are hydrogen atoms.

Neutrons: These are neutral (no charge) particles also located in the nucleus. Neutrons contribute to the atom's mass but do not affect its charge.

Electrons: These are negatively charged particles that orbit the nucleus in specific energy levels or shells. The number of electrons usually equals the number of protons in a neutral atom.

Analogy: Imagine the atom is like a soccer stadium. The nucleus (protons and neutrons) is like the center circle, and the electrons are like the fans running around the stadium. 2.

2. Atomic Number and Mass Number Atomic Number (Z): This is the number of protons in an atom's nucleus. It is unique to each element and determines its identity. The atomic number is usually located above the element symbol on the Periodic Table.

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

Calculating the Number of Neutrons: Number of neutrons = Mass Number (A) – Atomic Number (Z)

Example 1: Carbon (C) has an atomic number of 6 and a mass number of

1

2. How many neutrons does it have? Number of neutrons = 12 - 6 = 6 neutrons 2.

3. The Periodic Table The Periodic Table is a chart that organizes all known elements based on their atomic number and chemical properties. It’s arranged in rows (periods) and columns (groups).

Periods: These are the horizontal rows in the Periodic Table. Elements in the same period have the same number of electron shells. As you move across a period, the number of protons (and usually electrons) increases.

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

4. Electron Configuration Electrons are arranged in specific energy levels or shells around the nucleus. These shells can hold a certain number of electrons: 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 in Grade 8 (it can hold more, but we simplify it for this grade). The arrangement of electrons in these shells is called the electron configuration.

Example 2: Sodium (Na) has an atomic number of

1

1. Its electron configuration is 2, 8, 1 (2 electrons in the first shell, 8 in the second, and 1 in the third). 2.

5. Metals, Non-metals, and Metalloids Elements can be classified into three main categories: Metals: Generally shiny, malleable (can be hammered into sheets), ductile (can be drawn into wires), and good conductors of heat and electricity. Metals are typically found on the left side of the Periodic Table.

Examples: iron (Fe), copper (Cu), gold (Au). These are important in South African mining.

Non-metals: Generally dull, brittle, and poor conductors of heat and electricity. Non-metals are typically found on the right side of the Periodic Table.

Examples: oxygen (O), sulfur (S), carbon (C).

Metalloids (Semi-metals): Have properties of both metals and non-metals. They are often used as semiconductors in electronics.

Examples: silicon (Si), germanium (Ge). 2.6 Using the Periodic Table to predict Properties The Periodic Table is organized so elements with similar properties are grouped together. For example, Group 1 (alkali metals) are all very reactive metals. Group 17 (halogens) are all very reactive non-metals. Knowing the location of an element can give you clues about its properties. Guided Practice (With Solutions)

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

Solution: Atomic number (Z) = Number of protons = 17 Mass number (A) = Number of protons + Number of neutrons = 17 + 18 = 35 Looking at the Periodic Table, the element with an atomic number of 17 is chlorine (Cl).

Commentary: This question tests your understanding of the definitions of atomic number and mass number and your ability to use the Periodic Table to identify elements.

Question 2: Draw the electron configuration diagram for Magnesium (Mg) which has an atomic number of

1

2. Solution: Magnesium has 12 electrons. The first shell can hold a maximum of 2 electrons. So, the first shell has 2 electrons. The second shell can hold a maximum of 8 electrons. So, the second shell has 8 electrons. This leaves 12 - 2 - 8 = 2 electrons for the third shell.

Therefore, the electron configuration is 2, 8,

2. Commentary: This question assesses your understanding of how electrons fill the shells and how to represent this arrangement.

Question 3: Is Potassium (K) a metal, non-metal, or metalloid?