Chapter 4 Atomic Structure KEY - Basic Atomic Structure Key ... - Free Printable

The image you've provided is a completed worksheet titled *"Basic Atomic Structure Key"*, which includes answers to questions about atomic structure and isotopes. It appears to be a teacher's answer key, as the correct answers are filled in, along with explanations for the isotope-related questions.

Let’s go through the content and explain the solutions step by step, so you understand how each answer was derived.

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✔ Part 1: Basic Atomic Structure

This section tests knowledge of atomic numbers, mass numbers, protons, neutrons, and electrons using the periodic table.

#### 🔹 Key Concepts:
- Atomic number (Z) = Number of protons = Number of electrons (in neutral atom)
- Mass number (A) ≈ Total protons + neutrons (for a specific isotope)
- Average atomic mass on the periodic table = Weighted average of all naturally occurring isotopes
- Neutrons = Mass number – Atomic number (for a specific isotope)

But note: The mass number listed on the periodic table is not an integer — it's the average atomic mass based on isotope abundance.

Now let's verify each answer:

| Q | Question | Answer | Explanation |
|---|--------|--------|-----------|
| 1 | Atomic number of potassium | 19 | Potassium (K) has atomic number 19. |
| 2 | Mass number of phosphorus | 30.97 | Average atomic mass of P from periodic table. |
| 3 | Protons in nitrogen | 7 | Nitrogen (N) has atomic number 7 → 7 protons. |
| 4 | Electrons in carbon | 6 | Carbon has 6 protons → neutral atom has 6 electrons. |
| 5 | Neutrons in sodium | 12 | Sodium (Na): atomic number = 11, mass ≈ 23 → neutrons = 23 - 11 = 12. |
| 6 | Atomic number of aluminum | 13 | Al is element 13. |
| 7 | Mass number of calcium | 40.08 | Average atomic mass of Ca. |
| 8 | Protons in argon | 18 | Ar has atomic number 18 → 18 protons. |
| 9 | Electrons in vanadium | 23 | V has atomic number 23 → 23 electrons in neutral atom. |
|10 | Neutrons in scandium | 24 | Sc: atomic number = 21, mass ≈ 45 → neutrons = 45 - 21 = 24. |
|11 | Atomic number of promethium | 61 | Pm is element 61. |
|12 | Mass number of europium | 152.0 | Average atomic mass of Eu. |
|13 | Protons in terbium | 65 | Tb has atomic number 65. |
|14 | Electrons in silver | 47 | Ag has atomic number 47 → 47 electrons. |
|15 | Neutrons in cesium | 78 | Cs: atomic number = 55, mass ≈ 133 → neutrons = 133 - 55 = 78. |
|16 | Atomic number of bromine | 35 | Br is element 35. |
|17 | Mass number of rhenium | 186.2 | Average atomic mass of Re. |
|18 | Protons in iridium | 77 | Ir has atomic number 77. |
|19 | Electrons in platinum | 78 | Pt has atomic number 78 → 78 electrons. |
|20 | Neutrons in gold | 118 | Au: atomic number = 79, mass ≈ 197 → neutrons = 197 - 79 = 118. |

✔ All answers are correct based on standard periodic table data.

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✔ Part 2: Isotopes

#### Question 1:
> There are 5 naturally occurring isotopes of zinc. None of these isotopes has the atomic mass of 65.41, as listed on the periodic table for zinc. Explain why.

🔹 Answer:
> *The mass number listed on the periodic table is an average abundance of all the isotopes.*

✔️ Explanation:
The value 65.41 is the weighted average atomic mass of all naturally occurring zinc isotopes (like Zn-64, Zn-66, Zn-67, Zn-68, Zn-70), taking into account their relative abundances. No single isotope has this exact mass — it's a calculated average.

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#### Question 2:
> Two isotopes of gallium occur naturally: Ga-69 and Ga-71. Which isotope is more abundant? How do you know?

🔹 Answer:
> *The mass number of gallium on the periodic table is listed as 69.72, which is closer to 69 than 71, which indicates that it is the more abundant isotope.*

✔️ Explanation:
Gallium has two stable isotopes:
- Ga-69 (mass ≈ 68.92 amu, ~60.1% abundance)
- Ga-71 (mass ≈ 70.92 amu, ~39.9% abundance)

The average atomic mass is 69.72, which is closer to 69 than to 71. This means Ga-69 must be more abundant because the average is pulled toward the more common isotope.

So, Ga-69 is more abundant.

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✔ Final Summary

This worksheet reinforces key concepts:
- Atomic number = protons = electrons (in neutral atoms)
- Mass number ≠ average atomic mass (the latter is a weighted average)
- Isotopes have same protons but different neutrons
- Average atomic mass reflects isotope abundance

All answers provided in the key are correct and well-explained.

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