Study Notes on Structures and Properties of Matter

Module 1: Structures and Properties of Matter

Overview of Matter

  • Definition of Matter: Anything that has mass and occupies space (volume).

  • Three different types of matter:

    1. Elements: The simplest form of matter, consisting of only one type of atom.

    2. Compounds: Consisting of two or more different elements that are chemically bonded in a fixed ratio (e.g., Water). Can only be broken down via chemical reactions.

    3. Mixtures: Physical combination of substances, each retaining its chemical identity.

Pure Substances vs. Mixtures

  • Pure Substance: Has a constant composition and consistent properties throughout. Cannot be separated into other types of matter by physical means (like filtering or evaporating).

  • Mixtures: Two or more substances combined but not chemically bonded.

    • Homogeneous Mixture: Uniform composition throughout.

    • Heterogeneous Mixture: Non-uniform composition.

Atoms

  • Definition: The smallest particle of a chemical which can exist, overall electrically neutral in elemental form (protons = electrons).

  • Components of Atoms:

    1. Nucleus: Center containing protons and neutrons.

    2. Cloud of Electrons: Majority of volume, negatively charged, held together by electrostatic attraction with protons.

Atomic Symbols and Isotopes

  • Atomic Symbols:

    • Atomic Number: Number of protons.

    • Mass Number: Number of protons + number of neutrons.

    • Number of Neutrons: Mass number - number of protons.

  • Isotopes: Atoms with the same number of protons but different numbers of neutrons (e.g. Carbon-12, Carbon-13, Carbon-14).

    • Classification of Isotopes:

    1. Natural Isotopes: Found in nature (generally stable).

    2. Artificial Isotopes: Manufactured (generally unstable/radioactive).

Types of Matter Definitions

  1. Element: Made up of one atom from the periodic table.

  2. Molecule: A group of atoms bonded together, the smallest fundamental unit of a chemical compound that can take part in a chemical reaction.

  3. Compound: Two or more elements chemically combined.

  4. Mixture: A physical combination of substances.

  5. Gravimetric Analysis: Quantitative analysis of composition.

  6. Percentage Composition: Percentage of a particular substance in a mixture or compound.

Classification of Mixtures

  • Non-Pure Substances: Mixtures are classified as homogeneous or heterogeneous based on uniformity.

  • Mixtures can contain:

    1. Multiple different compounds.

    2. Different states of a compound.

    3. A combination of elements and compounds.

Separation Techniques

Different methods to separate mixtures:

  1. Sieving: Separates fine from coarse particles based on size. Uses perforated mesh.

  2. Magnetic Separation: Uses magnetism to separate magnetic substances.

  3. Filtration: Uses filter paper in a funnel to separate solids from liquids based on solubility.

  4. Sedimentation and Decantation: Allows sediments to settle before separating based on density.

  5. Distillation: Separates based on boiling point, involves vaporization and condensation.

  6. Evaporation and Crystallization: Removes solvent by evaporation, cooled liquid crystallizes.

  7. Separating Funnel: Used for immiscible liquids; releases the bottom layer through a stopcock.

Percentage Composition Calculation

  • Calculation Example: For Iron in Iron(III) oxide (Fe₂O₃)

    1. Mass of iron: 70g from 100g of Fe₂O₃.

    2. Percentage composition = rac{70}{100} imes 100 = 70 ext{%}.

  • General Calculation Formula: Mass of substance = total mass × percentage composition.

Types of Compounds

  1. Ionic Compounds: Consist of cations (positively charged) and anions (negatively charged). Example: Sodium Chloride (NaCl).

  2. Covalent Compounds: Formed by electron sharing, exist in molecular or network forms.

Covalent Molecular Compounds

  • Properties:

    • Generally low melting and boiling points.

    • Not electrically conductive.

    • Include diatomic molecules.

Covalent Network Compounds

  • Properties:

    • High melting points.

    • Non-conductors.

    • Discrete units forming a large structure (e.g. Diamond).

Bohr Model of Atom

  • Structure: Similar to solar system; Electrons in quantized shells (specific energy levels).

    • Ground State: Lowest energy state.

    • Excited State: State gained energy, allowing electron to move to a higher energy shell.

  • Photon Release: Occurs when electrons drop from excited to lower state, releasing energy.

Electron Configuration

  • Arrangement of electrons in shells:

    1. Shell: 2 electrons.

    2. Shell: up to 8 electrons.

    3. Shell: up to 18 electrons.

    4. Shell: up to 32 electrons.

    5. Shell: up to 50 electrons.

  • Valence Electrons: Electrons in the outermost shell.

  • Octet Rule: Atoms aim to have 8 valence electrons.

Schrodinger Model

  • Most modern model that uses quantum mechanics to describe electron positions.

  • Introduces the SPDF Notation for electrons.

VSEPR Theory

  • Definition: Valence Shell Electron Pair Repulsion Theory predicts the molecular shape based on electron pair repulsion in bonding and non-bonding pairs.

Intermolecular Forces

  1. Intra-molecular Bonds: Bonds within molecules.

  2. Inter-molecular Bonds: Forces between molecules (e.g., Dispersion Forces, Dipole-Dipole Forces, Hydrogen Bonds).

Allotropes

  • An element can have different stable forms (allotropes) with different chemical and physical properties due to variability in bonding.