chemistry semester 1 – honors review
name
6. how did new evidence support revisions to dalton’s indivisible atom theory? list or describe two pieces of evidence.
a.
b.
7. identify the three basic particles in the atom. give their location, charge, and mass. (fill in the table)

| particle | charge | mass (amu) | location |
|----------|--------|------------|----------|
| | | | |
| | | | |
| | | | |
8. the (protons/neutrons/electrons) contribute to the overall charge of an atom which is (positive/negative/neutral).
9. isotopes have the same number of (protons / neutrons) but a different number (protons / neutrons).
10. write the isotopic symbol for carbon-12 and carbon-14 including the atomic number and mass number:
11. fill in the blanks for the elements using the periodic table

| element | symbol | atomic # | #protons | # electrons | #neutrons | mass # |
|---------------|--------------|----------|----------|-------------|-----------|--------|
| hydrogen-3 | | | | | | |
| | | 74 | | | | 180 |
| | | | 33 | | 43 | |
| | $\frac{147}{61}$pm | | | | | |
| | | | | 92 | | 235 |
12. silicon has three naturally occurring isotopes. explain why the actual average atomic mass of silicon is closest to silicon-28.
a.

| isotope name | isotope mass (amu) | relative abundance (%) |
|--------------|--------------------|------------------------|
| silicon-28 | 27.98 | 92.21 |
| silicon-29 | 28.98 | 4.70 |
| silicon-30 | 29.97 | 3.09 |

is 1.1_b: nuclear stability
examples to practice:
13. what subatomic particle ratio determines nuclear stability in an atom?
14. what are the 3 main uses of nuclear science at this point in time?

Question

chemistry semester 1 – honors review
name
6. how did new evidence support revisions to dalton’s indivisible atom theory? list or describe two pieces of evidence.
   a.
   b.
7. identify the three basic particles in the atom. give their location, charge, and mass. (fill in the table)

| particle | charge | mass (amu) | location |
   |----------|--------|------------|----------|
   |          |        |            |          |
   |          |        |            |          |
   |          |        |            |          |
8. the (protons/neutrons/electrons) contribute to the overall charge of an atom which is (positive/negative/neutral).
9. isotopes have the same number of (protons / neutrons) but a different number (protons / neutrons).
10. write the isotopic symbol for carbon-12 and carbon-14 including the atomic number and mass number:
11. fill in the blanks for the elements using the periodic table

| element       | symbol       | atomic # | #protons | # electrons | #neutrons | mass # |
    |---------------|--------------|----------|----------|-------------|-----------|--------|
    | hydrogen-3    |              |          |          |             |           |        |
    |               |              | 74       |          |             |           | 180    |
    |               |              |          | 33       |             | 43        |        |
    |               | $\frac{147}{61}$pm |          |          |             |           |        |
    |               |              |          |          | 92          |           | 235    |
12. silicon has three naturally occurring isotopes. explain why the actual average atomic mass of silicon is closest to silicon-28.
    a.

| isotope name | isotope mass (amu) | relative abundance (%) |
    |--------------|--------------------|------------------------|
    | silicon-28   | 27.98              | 92.21                  |
    | silicon-29   | 28.98              | 4.70                   |
    | silicon-30   | 29.97              | 3.09                   |

is 1.1_b: nuclear stability
examples to practice:
13. what subatomic particle ratio determines nuclear stability in an atom?
14. what are the 3 main uses of nuclear science at this point in time?

Accepted Answer

### Question 6
# Brief Explanations:
To answer how new evidence supported revisions to Dalton’s indivisible atom theory, we recall key discoveries:
- **Discovery of electrons (e.g., Thomson’s cathode ray experiment)**: Showed atoms have negatively charged particles (electrons), so atoms are divisible (contain subatomic particles).
- **Discovery of the nucleus (Rutherford’s gold foil experiment)**: Showed most of an atom’s mass is concentrated in a tiny, positively charged nucleus, with electrons orbiting. This contradicted Dalton’s idea of a solid, indivisible atom.

# Answer:
a. Discovery of electrons (Thomson’s experiment) showed atoms contain subatomic particles (not indivisible).
b. Rutherford’s gold foil experiment revealed a dense, positively charged nucleus, proving atoms have internal structure (not solid/indivisible).

### Question 7
# Brief Explanations:
The three basic subatomic particles are protons, neutrons, and electrons. We recall their properties:
- **Proton**: Positive charge ($+1$), mass $1$ amu, located in the nucleus.
- **Neutron**: Neutral charge ($0$), mass $1$ amu, located in the nucleus.
- **Electron**: Negative charge ($-1$), mass $\approx 0$ amu (or $5.486 \times 10^{-4}$ amu), located in electron cloud/orbitals around the nucleus.

# Answer:
| Particle | Charge | Mass (amu) | Location |
|----------|--------|------------|----------|
| Proton   | $+1$ | $1$      | Nucleus  |
| Neutron  | $0$  | $1$      | Nucleus  |
| Electron | $-1$ | $\approx 0$ | Electron cloud (around nucleus) |

### Question 8
# Brief Explanations:
- **Protons** have a positive charge, **electrons** have a negative charge, and **neutrons** are neutral.
- In a neutral atom, the number of protons (positive charge) equals the number of electrons (negative charge), so the overall charge is neutral.
- Protons and electrons contribute to the atom’s charge (neutrons do not).

# Answer:
The (protons/electrons) contribute to the overall charge of an atom which is (neutral) (for a neutral atom; if ionized, charge changes, but typically atoms are neutral).
(Note: Fill in: “protons and electrons” for the first blank, “neutral” for the second. The question’s format implies choosing from the parentheses: “protons/electrons” (since neutrons are neutral) and “neutral” (for a neutral atom).)

### Question 9
# Brief Explanations:
Isotopes are atoms of the same element with the **same number of protons** (same atomic number, so same element) but a **different number of neutrons** (different mass number).

# Answer:
Isotopes have the same number of (protons) but a different number (neutrons).

### Question 10
# Brief Explanations:
The isotopic symbol is written as $\ce{^{A}_{Z}X}$, where:
- $Z$ = atomic number (number of protons),
- $A$ = mass number (protons + neutrons),
- $X$ = element symbol (carbon, $C$).

For carbon:
- **Carbon-12**: Atomic number $Z = 6$ (carbon has 6 protons), mass number $A = 12$. Symbol: $\ce{^{12}_{6}C}$.
- **Carbon-14**: Atomic number $Z = 6$, mass number $A = 14$. Symbol: $\ce{^{14}_{6}C}$.

# Answer:
Carbon-12: $\boldsymbol{\ce{^{12}_{6}C}}$
Carbon-14: $\boldsymbol{\ce{^{14}_{6}C}}$

### Question 11 (Table Completion)
We use atomic structure rules:
- Atomic number ($Z$) = #protons = #electrons (for neutral atoms).
- Mass number ($A$) = #protons + #neutrons.

#### Row 1: Hydrogen-3
- Element: Hydrogen-3 (isotope of H).
- Symbol: $\ce{^3_1H}$ (or $\ce{T}$ for tritium).
- Atomic # ($Z$): $1$ (H has 1 proton).
- #Protons: $1$.
- #Electrons: $1$ (neutral).
- #Neutrons: $A - Z = 3 - 1 = 2$.
- Mass #: $3$.

#### Row 2: Atomic # = 74
- Atomic # = 74 → element is tungsten ($W$).
- #Protons: $74$.
- #Electrons: $74$ (neutral).
- #Neutrons: $A - Z = 180 - 74 = 106$.
- Mass #: $180$.

#### Row 3: #Protons = 33, #Neutrons = 43
- #Protons = 33 → atomic # = 33 → element is arsenic ($As$).
- Symbol: $As$.
- Atomic #: $33$.
- #Electrons: $33$ (neutral).
- Mass #: $33 + 43 = 76$.

#### Row 4: $\ce{^{147}_{61}Pm}$ (Promethium)
- Atomic # ($Z$): $61$ (bottom left).
- #Protons: $61$.
- #Electrons: $61$ (neutral).
- #Neutrons: $147 - 61 = 86$.
- Mass #: $147$.

#### Row 5: #Electrons = 92, Mass # = 235
- #Electrons = 92 → #protons = 92 (neutral atom) → atomic # = 92 → element is uranium ($U$).
- Symbol: $U$.
- Atomic #: $92$.
- #Protons: $92$.
- #Neutrons: $235 - 92 = 143$.

# Filled Table:

| Element       | Symbol   | Atomic # | #Protons | #Electrons | #Neutrons | Mass # |
|---------------|----------|----------|----------|------------|-----------|--------|
| Hydrogen-3    | $\ce{^3_1H}$ | $1$    | $1$    | $1$      | $2$     | $3$  |
| Tungsten      | $W$    | $74$   | $74$   | $74$     | $106$   | $180$ |
| Arsenic       | $As$   | $33$   | $33$   | $33$     | $43$    | $76$  |
| Promethium    | $\ce{^{147}_{61}Pm}$ | $61$   | $61$   | $61$     | $86$    | $147$ |
| Uranium       | $U$    | $92$   | $92$   | $92$     | $143$   | $235$ |

### Question 12
# Brief Explanations:
The average atomic mass of an element is a **weighted average** of its isotopes’ masses, weighted by their relative abundances.

For silicon:
- Silicon-28 has a relative abundance of $92.21\%$ (much higher than Silicon-29 ($4.70\%$) and Silicon-30 ($3.09\%$)).
- A higher abundance means Silicon-28 contributes more to the average atomic mass, so the average is closest to Silicon-28’s mass (27.98 amu).

# Answer:
a. The average atomic mass is a weighted average. Silicon-28 has the highest relative abundance ($92.21\%$) among the isotopes. Since it is the most abundant, it has the greatest influence on the average, making the actual average atomic mass closest to Silicon-28’s mass.

### Question 13
# Brief Explanations:
Nuclear stability is determined by the **ratio of neutrons to protons ($n/p$ ratio)** in the nucleus. For light elements (low atomic number), stability is around $n/p \approx 1$; for heavier elements, a higher $n/p$ (closer to $1.5$) is stable.

# Answer:
The subatomic particle ratio that determines nuclear stability is the **neutron-to-proton ($n/p$) ratio** (ratio of neutrons to protons in the nucleus).

### Question 14
# Brief Explanations:
Nuclear science has three main uses:
- **Energy production**: Nuclear power plants use fission (e.g., uranium-235) to generate electricity.
- **Medicine**: Radioisotopes for diagnostics (e.g., $^{18}\text{F}$ in PET scans) and therapy (e.g., $^{131}\text{I}$ for thyroid cancer).
- **Research/Industry**: Radioactive tracers for studying chemical reactions, sterilization of medical equipment/food, and materials analysis (e.g., carbon dating).

# Answer:
The three main uses of nuclear science are:
1. **Nuclear energy production** (via fission in power plants).
2. **Medical applications** (diagnostics, cancer therapy with radioisotopes).
3. **Industrial/Research uses** (sterilization, radioactive tracers, carbon dating).

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