YG

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.