4.1.1 A Simple Model of the Atom, Symbols, Relative Atomic Mass, Electronic Charge and Isotopes

4.1.1.1 Atoms, Elements, and Compounds

• Atoms: Smallest part of an element that can exist, represented by chemical symbols (e.g., O for oxygen, Na for sodium).
• Elements: Consist of one type of atom, about 100 different elements shown in the periodic table.
• Compounds: Formed from elements via chemical reactions, involve formation of new substances and energy changes, contain two or more elements combined in fixed proportions, represented by formulae, can only be separated by chemical reactions.
• Chemical Reactions: Represented by word equations or symbols/formulae.
• Exam Skills:
  • Use names/symbols of first 20 elements, Groups 1 and 7, and other specified elements.
  • Name compounds from given formulas or symbol equations.
  • Write word equations and balanced chemical equations (HT: half equations, ionic equations).

4.1.1.2 Mixtures

• Definition: Consist of two or more elements or compounds not chemically combined; properties unchanged.
• Separation: Physical processes (filtration, crystallization, distillation, chromatography) used for separation without chemical reactions or forming new substances.
• Exam Skills:
  • Describe, explain, and provide examples of separation processes.
  • Suggest suitable separation/purification techniques for mixtures.

4.1.1.3 Development of the Model of the Atom

• Model Changes: New evidence can change or replace scientific models.
• **Historical Models: **
  • Pre-electron: Atoms were indivisible tiny spheres.
  • Plum Pudding Model: Atom as positive charge ball with embedded electrons.
  • Nuclear Model: Post-alpha particle scattering experiment, mass concentrated at nucleus.
  • Bohr’s Model: Electrons orbit nucleus at specific distances, supported by calculations.
  • Proton Discovery: Positive charge in nucleus subdivided into protons.
  • Neutron Discovery: Chadwick's experiments confirmed neutrons in the nucleus.
• Exam Skills:
  • Explain model changes based on scattering experiment.
  • Differentiate between plum pudding and nuclear models.

4.1.1.4 Relative Electrical Charges of Subatomic Particles

• Charges:
  • Proton: +1
  • Neutron: 0
  • Electron: -1
• Neutrality: Atoms are neutral, having equal numbers of protons and electrons.
• Atomic Number: Reflects number of protons, unique to each element.
• Exam Skills:
  • Describe atoms using the nuclear model.

4.1.1.5 Size and Mass of Atoms

• Atom Size: Radius ~0.1 nm; nucleus radius <1/10,000 of atom.
• Mass: Concentrated in nucleus.
• Relative Masses:
  • Proton: 1
  • Neutron: 1
  • Electron: Very small
• Mass Number: Sum of protons and neutrons.
• Isotopes: Atoms of an element with different neutron numbers.
• Exam Skills:
  • Calculate protons, neutrons, electrons from atomic/mass numbers.

4.1.1.6 Relative Atomic Mass

• Definition: Average value considering isotopic abundance.
• Exam Skills:
  • Calculate relative atomic mass from isotope abundance.

4.1.1.7 Electronic Structure

• Energy Levels: Electrons occupy lowest available levels; can be represented by numbers or diagrams.
  • Example: Sodium’s structure is 2,8,1.
• Exam Skills:
  • Represent electronic structures for first twenty elements both numerically and diagrammatically.