Lesson Notes By Weeks and Term v5 - Grade 8

Lesson Video

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Performance objectives

• Identify protons, neutrons, and electrons.
• Calculate the number of particles in an atom.
• Explain what isotopes are.
• Describe the layout of the periodic table.

Lesson summary

This week, we delve into the fascinating world of atomic structure and the periodic table. Understanding atoms, the basic building blocks of all matter, is crucial for understanding everything around us – from the air we breathe to the soil that grows our food. The periodic table, a highly organized chart of all known elements, provides a framework for understanding the properties and behavior of these atoms. Why does this matter to you, a South African learner? South Africa is rich in mineral resources like gold, platinum, and diamonds – all elements found on the periodic table.

Lesson notes

2.1 Atomic Structure All matter is made up of tiny particles called atoms. Atoms are not indivisible, as was once thought. They consist 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 an atom is. For example, all atoms with 6 protons are carbon atoms. The number of protons is also equal to the atomic number (symbol: Z).

Neutrons: Neutral (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. Atoms are electrically neutral because they have the same number of protons and electrons.

Key Definitions: Atomic Number (Z): The number of protons in the nucleus of an atom. This defines the element. The atomic number is located above the element's symbol on the periodic table.

Mass Number (A): The total number of protons and neutrons in the nucleus of an atom. Mass Number = Number of Protons + Number of Neutrons Neutral Atom: An atom with no overall charge. Number of Protons = Number of Electrons Calculating the number of subatomic particles: Protons: Number of protons = Atomic Number (Z)

Electrons: In a neutral atom, Number of electrons = Atomic Number (Z)

Neutrons: Number of Neutrons = Mass Number (A) - Atomic Number (Z)

Example 1: Determine the number of protons, neutrons, and electrons in a neutral sodium (Na) atom, given that its atomic number is 11 and its mass number is

2

3. Protons: Atomic number = 11, so there are 11 protons.

Electrons: Neutral atom, so number of electrons = number of protons = 11 electrons.

Neutrons: Mass number - Atomic number = 23 - 11 = 12 neutrons.

Example 2: Determine the number of protons, neutrons, and electrons in a neutral chlorine (Cl) atom, given that its atomic number is 17 and its mass number is

3

5. Protons: Atomic number = 17, so there are 17 protons.

Electrons: Neutral atom, so number of electrons = number of protons = 17 electrons.

Neutrons: Mass number - Atomic number = 35 - 17 = 18 neutrons. 2.2 Isotopes Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. Since they have the same number of protons, they have the same atomic number and are the same element.

However, because they have different numbers of neutrons, they have different mass numbers.

Example: Carbon has two common isotopes: Carbon-12 (¹²C) and Carbon-14 (¹⁴C). Both have 6 protons (atomic number = 6), but Carbon-12 has 6 neutrons (12-6 = 6), while Carbon-14 has 8 neutrons (14-6 = 8).

Relative Atomic Mass: The relative atomic mass of an element is the weighted average of the masses of its isotopes, taking into account their natural abundances.

Formula: Relative Atomic Mass = [(% abundance of isotope 1 x mass of isotope 1) + (% abundance of isotope 2 x mass of isotope 2) + ... ] / 100 Example 3: Chlorine has two naturally occurring isotopes: Chlorine-35 (³⁵Cl) with a mass of 35 amu and an abundance of 75.77%, and Chlorine-37 (³⁷Cl) with a mass of 37 amu and an abundance of 24.23%. Calculate the relative atomic mass of chlorine. Relative Atomic Mass = [(75.77 x 35) + (24.23 x 37)] / 100 = [2651.95 + 896.51] / 100 = 3548.46 / 100 = 35.48 amu Therefore, the relative atomic mass of chlorine is approximately 35.48 amu. This value is found on most periodic tables. 2.3 The Periodic Table The periodic table is an organized arrangement of all known elements in order of increasing atomic number. It is a powerful tool that helps us understand the properties and relationships between different elements.

Periods: Horizontal rows on the periodic table. Elements in the same period have the same number of electron shells.

Groups (or Families): Vertical columns on 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). Metals, Nonmetals, and Metalloids: Elements are broadly classified into metals, nonmetals, and metalloids (also known as semi-metals).

Metals: Generally located 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: Sodium (Na), Iron (Fe), Copper (Cu), Gold (Au), Platinum (Pt) (important elements for South African mining).

Nonmetals: Generally located on the right side of the periodic table. They are typically dull, poor conductors of heat and electricity, and brittle.

Examples: Oxygen (O), Nitrogen (N), Chlorine (Cl), Sulfur (S).

Metalloids: Have properties of both metals and nonmetals. They are located along the "staircase" line that separates metals and nonmetals.

Examples: Silicon (Si), Germanium (Ge).