Understanding Atoms and Radioactivity

6.1 Inside the Atom

6.1.1 Introduction to Atomic Structure

  • Historical Model:
      - The atom was originally conceptualized using the Plum Pudding Model.
      - Developed by English chemist J.J. Thomson.
      - Depicted negatively charged electrons embedded in a positively charged sphere.
      - Current Understanding:
        - This model has since been disproven.
        - Atoms are now understood to be the smallest unit of matter and are not easily observable under a microscope.

  • Scientific Models:
      - Models and theories are crafted based on prior knowledge, experimental results, and observational data.
      - Scientists perform experiments multiple times, often modifying conditions slightly in each trial.
      - Data collected is carefully analyzed, and a coherent model is constructed to explain observations.
      - Models offer utility in predicting behaviors and explaining phenomena.
      - Evolution of Models:
        - New discoveries necessitate updates to existing models for improved accuracy in explaining observations.
      - This is a hallmark of the scientific process, highlighting the continuous improvement of our understanding of the universe.

6.1.2 Questions for Thought

  • Connection between Radioactivity and its Uses:
      1. How does radioactivity play a role in cancer treatment?
      2. What is the correlation between radioactivity and fossils?

  • Understanding Atoms:
      1. How did the Plum Pudding Model help clarify atomic structure?
      2. In what way did Lord Rutherford's experiments using solid gold determine that atoms are mainly empty space?
      3. What phenomena causes radioactivity?
      4. Is radioactivity universally dangerous?
      5. How is uranium utilized within a nuclear reactor?

6.1.3 Science Inquiry

Composition of Matter

  • Matter is composed of three groups:
      1. Elements:
         - Substances composed of only one type of atom.
      2. Compounds:
         - Composed of two or more different types of atoms bonded together.
      3. Mixtures:
         - Composed of two or more substances that are not chemically bonded.

  • Basic Concepts:
      1. Atoms vs. Molecules:
         - Atom: The basic unit of a chemical element.
         - Molecule: A group of two or more atoms bonded together.
      2. Example of an element in molecular form:
         - Oxygen exists as O2O_2.
      3. Examples of compounds made up of molecules:
         - Water: H2OH_2O, Carbon dioxide: CO2CO_2.
      4. A compound not made of molecules:
         - Sodium chloride: NaClNaCl.

Particles Inside an Atom

  • Key particles found within an atom:
      1. Protons
      2. Neutrons
      3. Electrons

Identifying Atoms and Molecules

  • Different types of diagrams can represent:
      1. An atom of an element
      2. A molecule of an element
      3. A molecule of a compound

6.1 Topic 6 Pre-test

  • Q1: Every proton in an atom has a ___ electric charge.
      - Options: Positive, Negative, Zero, Variable

  • Q2: Which particles are in the nucleus?
      - Options:
        - A: Electrons
        - B: Neutrons
        - C: Protons

  • Q3: Different isotopes of the same element contain different numbers of:
      - Options:
        - A: Electrons
        - B: Protons
        - C: Neutrons

  • Q4: Most of the volume in an atom is composed of:
       - Options:
        - Air
        - Electrons
        - Empty space
        - Nucleus

  • Q5: True or false? All radioactive substances are artificially made.
      - Answer: False

  • Q6: How many protons are present in every atom of hydrogen?
      - Explain your answer.

  • Q7: (Follow-up to Q6) How many electrons are present in every neutral atom of hydrogen?
      - Explain your answer.

  • Q8: Which particles orbit the nucleus of an atom?

  • Q9: Where is most of the mass of the atom located?

  • Q10: How are neutrons different from protons?

  • Q11: Which two atoms U, V, X and Y are of the same element?
      - Details:
        - Atom U: 11 protons, 13 neutrons, 11 electrons
        - Atom V: 13 protons, 11 neutrons, 13 electrons
        - Atom X: 12 protons, 11 neutrons, 13 electrons
        - Atom Y: 11 protons, 12 neutrons, 11 electrons

  • Q12: Identify the type of nuclear radiation:
      - (a) Consists of helium nuclei containing two protons and two neutrons
      - (b) Travels at the speed of light
      - (c) Has the same size and mass as electrons

  • Q13-14: Identify which of alpha, beta or gamma radiation can be easily stopped by human skin or paper.

  • Q15: Graph Analysis:
      - Analyze the radioactive decay of 100 grams of strontium-90 used for spacecraft power.
      - (a) Determine the mass of strontium-90 remaining after 56 years.
      - (b) Estimate the half-life of strontium-90.