indicates a physical change.
atomic theory bohr, democritus and rutherford experiment: write their main points out.
recall they all understood atoms to be the smallest units of matter
bohr model of ca:
rutherford experiment drawing and how nucleus was invented:
density:
what is the volume of an object with the density of 5.4g/ml and mass of 20g.
conversions: convert 10 ml to l.
mixture separation:
what properties are you using to separate, sand, salt and fe filings?
what happens during a phase change in terms of energy? solid to liquid to gas.

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Accepted Answer

# Brief Explanations:
1. **Atomic theory summaries**:
    - Democritus: Proposed matter is made of indivisible, indestructible tiny particles called atoms; different substances have different atom shapes/sizes.
    - Bohr: Electrons orbit the nucleus in fixed, circular energy levels; electrons absorb/release energy to jump between levels.
    - Rutherford experiment: Fired alpha particles at gold foil; most passed through, some deflected. This led to the discovery of the dense, positively charged atomic nucleus, as deflections showed concentrated positive mass at the atom's center.
2. **Bohr model of Ca**: Calcium has an atomic number of 20. Its Bohr model has 4 energy levels: 2 electrons in the first level, 8 in the second, 8 in the third, and 2 in the outermost (fourth) level.
3. **Density calculation**: Use the density formula rearranged to solve for volume.
4. **Unit conversion**: Use the conversion factor 1 L = 1000 mL.
5. **Mixture separation properties**: Use magnetism for iron filings, solubility for salt, and particle size for sand.
6. **Phase change energy**: Energy is absorbed/released to break/form intermolecular forces without changing chemical identity.

# Answer:
1. **Atomic theory main points**:
    - Democritus: Matter is made of indivisible, indestructible atoms; different atoms have different shapes and sizes.
    - Bohr: Electrons occupy fixed, discrete circular energy levels (shells) around the nucleus; electrons absorb or emit energy when moving between levels.
    - Rutherford experiment:
      - **Drawing**: A source of alpha particles directed at a thin gold foil, surrounded by a fluorescent screen to detect deflected particles.
      - **Nucleus discovery**: Most alpha particles passed straight through the foil, showing atoms are mostly empty space. A small fraction of particles were deflected at large angles, indicating a dense, positively charged central region (the nucleus) that repels the positively charged alpha particles.
2. **Bohr model of Ca**: A central nucleus with 20 protons and 20 neutrons, surrounded by 4 electron shells: 2 electrons in the 1st shell, 8 in the 2nd, 8 in the 3rd, and 2 in the 4th (outer) shell.
3. **Density problem**:
    ## Step1: Rearrange density formula for volume
    $	ext{Volume} = \frac{	ext{Mass}}{	ext{Density}}$
    ## Step2: Substitute given values
    $	ext{Volume} = \frac{20\ 	ext{g}}{5.4\ 	ext{g/ml}} \approx 3.70\ 	ext{ml}$
    Answer: $\approx 3.70\ 	ext{ml}$
4. **Conversions**:
    ## Step1: Use 1 L = 1000 ml conversion factor
    $10\ 	ext{ml} 	imes \frac{1\ 	ext{L}}{1000\ 	ext{ml}}$
    ## Step2: Calculate the result
    $= 0.01\ 	ext{L}$
    Answer: $0.01\ 	ext{L}$
5. **Mixture Separation properties**:
    - Iron filings: Use magnetism (magnetic attraction, since Fe is magnetic and sand/salt are not).
    - Salt: Use solubility (salt dissolves in water, sand does not; filter to separate sand, then evaporate water to get salt).
    - Sand: Use particle size (filtration, since sand particles are too large to pass through filter paper, while dissolved salt passes through).
6. **Phase change energy**:
    - Solid to liquid (melting): Energy is absorbed to break intermolecular forces holding the solid structure together, increasing particle kinetic energy and allowing particles to move freely in the liquid state.
    - Liquid to gas (vaporization/boiling): Energy is absorbed to overcome remaining intermolecular forces, allowing particles to move independently in the gaseous state.
    - Gas to liquid (condensation): Energy is released as intermolecular forces form between gas particles, reducing their kinetic energy.
    - Liquid to solid (freezing): Energy is released as intermolecular forces lock particles into a rigid solid structure.
    - Solid to gas (sublimation): Energy is absorbed to directly break all intermolecular forces holding the solid together, transitioning particles to the gaseous state.
    - Gas to solid (deposition): Energy is released as intermolecular forces form to lock gaseous particles directly into a solid structure.

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Explanation:

Answer:

Step1: Rearrange density formula for volume

Step2: Substitute given values