Chemistry 2023

Year 8 Science - Chemistry Properties of Materials

Assessments

• Acids and Bases Practical Report: 15%, Week 4

• Chemistry Topic Test: 20%, Week 9

The Periodic Table - Introduction

• Atoms are composed of:

  • Protons: Positively charged particles with mass

  • Electrons: Negatively charged particles with negligible mass

  • Neutrons: Neutral particles with mass

• Protons and neutrons are in the nucleus, while electrons orbit around it.

The Periodic Table – Structure

• Columns: Groups

• Rows: Periods

The Periodic Table – Element Properties

• Elements are arranged by properties.

• Example with Hydrogen:

  • Atomic Number: Equal to number of protons

  • Atomic Symbol: Unique identifier for each element

  • Atomic Mass: Total of protons and neutrons

The Periodic Table – Subatomic Particle Determination

• From the Periodic Table:

  • Protons = Atomic Number

  • Electrons = Protons

  • Neutrons = Atomic Mass - Atomic Number

Classification of Elements

• Metals: Good conductors of heat/electricity, malleable, and generally solids.

• Non-Metals: Poor conductors, generally not malleable, mostly gases.

• Metalloids: Properties of both metals and non-metals.

Special Groups in the Periodic Table

• Noble Gases: Least reactive, full valence electrons, odorless, gaseous at room temperature.

• Halogens: Most reactive non-metals, 7 valence electrons, toxic, gaseous at room temperature.

Alkali Metals

• Highly reactive, silvery, with 1 valence electron.

Alkaline Earth Metals

• Shiny, silvery-white, with 2 valence electrons, solids at room temperature.

Transition Metals

• Varying valence electron counts, good heat/electricity conductors (e.g., Copper, Iron).

Rare Earth Elements

• Final group, include rare and radioactive metals, stable as solids at room temperature.

Atomic Structure Introduction

• Atoms consist of protons, neutrons, and electrons; electrons orbit the nucleus in shells.

Electron Shells

• Neils Bohr's model: Electrons occupy unique shells:

  • 1st Shell: Max 2 electrons

  • 2nd Shell: Max 8 electrons

  • 3rd Shell: Can hold 18 electrons (usually fills with 8 before next shell)

Ion Formation Through Electron Transfer

• Atoms prefer full or empty valence shells, leading to positive (Cation) or negative charges (Anion).

• Example: Sodium (Na) loses 1 electron to become Na+; Fluorine (F) gains 1 electron to become F−.

Neutrons

• Neutrons help determine atomic mass but do not affect charge. The number of neutrons can be calculated as:

  • Neutrons = Relative Atomic Mass - Atomic Number.

Protons

• Changing the number of protons changes the element.

Acids and Bases

• Acids: Proton donors (pH < 7). Found in foods, cleaning products.

• Bases: Proton acceptors (pH > 7). Found in soaps, cleaning products.

pH Scale

• Measures acidity or basicity:

  • Acidic: pH < 7

  • Neutral: pH = 7

  • Basic: pH > 7

Measuring pH

• Methods:

  • Indicators: Change color in acids/bases (Universal Indicator).

  • Litmus Paper: Red turns blue for bases; blue turns red for acids.

Neutralization

• Chemical reaction between acids and bases producing water and salt:

  • Equation: Acid + Base → Water + Salt.

Chemical Bonding

• Ionic Bonding: Formation of compounds through attraction between cations and anions (e.g., NaF).

• Covalent Bonding: Sharing of electrons between atoms.

• Metallic Bonding: Formation of a "sea of electrons", resulting in strong, conductive properties.