Free Printable Atomic Structure And Isotopes Worksheets - Free Printable

Here are the solutions to the problems in your worksheet.

Part A: Atomic Structure

1. Complete the following table.

To solve this, remember these rules for neutral atoms (atoms with no charge):
* Atomic Number = Number of Protons = Number of Electrons
* Mass Number = Number of Protons + Number of Neutrons
* Number of Neutrons = Mass Number - Atomic Number

* Row 1: We have a Mass number of 70. Looking at the periodic table, element 31 is Gallium (Ga). If we assume it's the most common isotope or simply looking for an integer fit, let's look closer. Actually, usually, these problems give you one key piece of info like the Element Name or Symbol. Here, the "Element name" column is blank. Let's look at the other rows first to see if there is a pattern or if I missed a clue. Ah, wait. Usually, you identify the element by its proton count.
* Let's look at Row 4 first: It has 35 protons. Element 35 is Bromine (Br). Since it's neutral, it has 35 electrons. The atomic number is 35. The mass number isn't given, but standard Bromine is often roughly 80 (specifically Br-79 and Br-81). However, without a specific mass number given, we can't calculate exact neutrons unless we assume the most common isotope or if there's a typo in my reading. Let's re-read carefully.
* Actually, let's look at Row 1 again. Just "70" under Mass Number. This is ambiguous without the element name. Let's look at Row 2.
* Row 2: Atomic number is 48. Element 48 is Cadmium (Cd). So, Protons = 48, Electrons = 48. We don't have a mass number, so we can't find neutrons yet.
* Row 3: Electrons = 80. For a neutral atom, Protons = 80. Element 80 is Mercury (Hg). Atomic number = 80. Again, no mass number.
* Row 4: Protons = 35. Element 35 is Bromine (Br). Electrons = 35. Atomic number = 35.

*Self-Correction:* Often in these worksheets, if a cell is blank, you might need to look up standard atomic weights or there is missing context. However, looking at Row 1, "70" is the mass number. Is there an element with mass number 70 that is commonly used? Zinc-70? Germanium-70?
Let's look at the structure again.
Maybe I should provide the variables based on the Periodic Table for the identified elements.

* Row 1: Let's assume the question implies finding the element *if* we knew the protons, or vice versa. Wait, looking at similar online worksheets, sometimes specific isotopes are implied. Let's look at Row 2: Cd-48? No, 48 is the atomic number.
Let's try to fill in what is definitely known from the Periodic Table.

* Row 2 (Atomic # 48): Element is Cadmium. Protons: 48. Electrons: 48.
* Row 3 (Electrons 80): Neutral atom means Protons = 80. Element is Mercury. Atomic #: 80.
* Row 4 (Protons 35): Element is Bromine. Atomic #: 35. Electrons: 35.

*Re-evaluating Row 1:* If the mass number is 70, and we don't know the element, we can't solve it uniquely. HOWEVER, looking at the layout, perhaps the student is expected to pick a common element? Or maybe I am missing a subtle clue. Let's look at the second part of the worksheet. It deals with specific isotopes.

Let's look at the provided solution for Row 1 in typical keys. Often, Zinc (Zn) has a mass number of roughly 65, Germanium (Ge) is 72/73/74. Ytterbium? No.
Actually, let's look at Gallium. Ga-69 and Ga-71 are common.
Let's look at Zinc. Zn-64, 66, 67, 68, 70. Zinc-70 is a stable isotope. If the element was Zinc, Atomic # is 30. Protons 30, Electrons 30, Neutrons 40.
Let's look at Germanium. Ge-70 is also a stable isotope. Atomic # 32. Protons 32, Electrons 32, Neutrons 38.

*Alternative interpretation:* Is it possible the first row corresponds to an element mentioned elsewhere? No.
Let's look at the numbers again. 70, 48, 80, 35.
There is a possibility that Row 1 is Ytterbium? No.

Let's assume the most likely intended answer for a general chemistry class where "70" is the mass number. Without the element name, it is technically unsolvable. BUT, if we look at Row 2, 48 is Cadmium. Row 3, 80 is Mercury. Row 4, 35 is Bromine.

Let's look at the image again very closely.
Row 1: Mass Number 70.
Row 2: Atomic Number 48.
Row 3: Electrons 80.
Row 4: Protons 35.

Okay, I will provide the answers for Rows 2, 3, and 4 which are definitive. For Row 1, since it is ambiguous, I will note that the element name is required. *However*, in many such worksheets, if the mass number is 70, it might refer to Ytterbium-170? No. Tin-118? No.

Wait! Look at the spacing. Is it possible the "70" belongs to the element Gallium (approx mass 69.7)? Or Germanium (72.6)? Or Zinc (65.4)?
Actually, there is a common isotope $^{70}Ge$ (Germanium-70) and $^{70}Zn$ (Zinc-70).
Let's check if there is a pattern in the atomic numbers: 30, 48, 80, 35? No obvious pattern.

Let's look at the prompt again. "Complete the following table."
I will solve the ones that are chemically unique (Rows 2-4) and for Row 1, I will provide the data for Zinc-70 as a likely candidate, but add a note. Actually, looking at the other numbers (48, 80, 35), they are all atomic numbers/proton counts effectively.

Let's try one more thing. Is it possible the first row is Ytterbium? No.
How about Nitrogen? No.

Let's stick to the definitive ones for the final output and explain the logic.

Row 2: Atomic Number 48 $\rightarrow$ Cadmium (Cd).
Protons: 48
Electrons: 48
Neutrons: Depends on isotope. Common mass is 112. Neutrons = $112 - 48 = 64$. (I will leave Neutrons/Mass blank or use average if not specified, but usually, these tables want specific integers. I'll use the most abundant isotope: Cd-114 is common too. Let's just list Protons/Electrons/Symbol).

Row 3: Electrons 80 $\rightarrow$ Protons 80 $\rightarrow$ Mercury (Hg).
Atomic Number: 80
Protons: 80
Symbol: Hg
Neutrons: Common isotope Hg-202. Neutrons = $202 - 80 = 122$.

Row 4: Protons 35 $\rightarrow$ Bromine (Br).
Atomic Number: 35
Electrons: 35
Symbol: Br
Neutrons: Common isotope Br-79 or Br-81. Let's use Br-79. Neutrons = $79 - 35 = 44$.

*Correction for Row 1*: In many textbook examples, if only Mass Number 70 is given, it is often paired with Atomic Number 30 (Zinc) or 32 (Germanium). Without the element name, I cannot be 100% sure. However, I will provide the breakdown for Zinc-70 as it is a very standard example, but I will explicitly state that the element name is needed to be certain.

*Actually*, looking at the worksheet source style (ChemistryLearner), they often use standard integers. Let's look at Part B. It uses specific isotopes like H-1, H-2, He-4. This suggests Part A might also rely on specific common isotopes.

Let's provide the definite answers for 2, 3, 4 and a "Likely" answer for 1 with an explanation.

2. Identify the neutral atom described by name and mass number.

* i) The atom with 2 neutrons and 1 proton:
* Protons = 1 $\rightarrow$ Hydrogen (H).
* Mass Number = Protons + Neutrons = $1 + 2 = 3$.
* Answer: Hydrogen-3 (or Tritium).

* ii) The atom with 17 electrons and 18 neutrons:
* Neutral atom $\rightarrow$ Protons = Electrons = 17.
* Element 17 is Chlorine (Cl).
* Mass Number = Protons + Neutrons = $17 + 18 = 35$.
* Answer: Chlorine-35.

* iii) The atom with 6 protons and 8 neutrons:
* Protons = 6 $\rightarrow$ Carbon (C).
* Mass Number = Protons + Neutrons = $6 + 8 = 14$.
* Answer: Carbon-14.

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Part B: Isotope

1. Complete the following table.

Rules:
* Symbol format: $^{A}_{Z}X^{charge}$
* $A$ (top left) = Mass Number = Protons + Neutrons
* $Z$ (bottom left) = Atomic Number = Protons
* $X$ = Element Symbol
* Charge (top right) = Protons - Electrons
* # of Protons = Atomic Number ($Z$)
* # of Neutrons = Mass Number ($A$) - Protons ($Z$)
* # of Electrons = Protons ($Z$) - Charge (if positive ion, subtract charge; if negative, add magnitude of charge). For neutral atoms, Electrons = Protons.

Left Column:

1. $^1H_1$:
* Protons ($Z$): 1
* Mass ($A$): 1
* Neutrons: $1 - 1 = 0$
* Electrons: 1 (Neutral)

2. $^2H_1$:
* Protons ($Z$): 1
* Mass ($A$): 2
* Neutrons: $2 - 1 = 1$
* Electrons: 1 (Neutral)

3. $^4He_2$:
* Protons ($Z$): 2
* Mass ($A$): 4
* Neutrons: $4 - 2 = 2$
* Electrons: 2 (Neutral)

4. $^5He_2$:
* Protons ($Z$): 2
* Mass ($A$): 5
* Neutrons: $5 - 2 = 3$
* Electrons: 2 (Neutral)

5. $^6Li_3$:
* Protons ($Z$): 3
* Mass ($A$): 6
* Neutrons: $6 - 3 = 3$
* Electrons: 3 (Neutral)

6. $^7Li_3$:
* Protons ($Z$): 3
* Mass ($A$): 7
* Neutrons: $7 - 3 = 4$
* Electrons: 3 (Neutral)

Right Column:

1. $^{17}O_8$:
* Protons ($Z$): 8
* Mass ($A$): 17
* Neutrons: $17 - 8 = 9$
* Electrons: 8 (Neutral)

2. $^{39}K_{19}$:
* Protons ($Z$): 19
* Mass ($A$): 39
* Neutrons: $39 - 19 = 20$
* Electrons: 19 (Neutral)

3. $^{40}Ca_{20}$:
* Protons ($Z$): 20
* Mass ($A$): 40
* Neutrons: $40 - 20 = 20$
* Electrons: 20 (Neutral)

4. $^{235}U_{92}$:
* Protons ($Z$): 92
* Mass ($A$): 235
* Neutrons: $235 - 92 = 143$
* Electrons: 92 (Neutral)

5. $^{244}Pu_{94}$:
* Protons ($Z$): 94
* Mass ($A$): 244
* Neutrons: $244 - 94 = 150$
* Electrons: 94 (Neutral)

6. $^{56}Fe_{26}^{3+}$:
* Protons ($Z$): 26
* Mass ($A$): 56
* Neutrons: $56 - 26 = 30$
* Electrons: The charge is $3+$, meaning it lost 3 electrons.
* Calculation: $26 - 3 = 23$.

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Final Answer:

Part A: Atomic Structure

1. Table Completion
*(Note: For Row 1, the element name is missing in the problem. Based on common isotopes with mass 70, it is likely Zinc-70 or Germanium-70. I have provided Zinc-70 below as a common example, but please check with your teacher if a specific element was discussed in class. Rows 2-4 are definitive based on atomic number.)*

| Element name | Atomic number | Mass number | Number of protons | Number of electrons | Number of neutrons | Element symbol |
| :--- | :---: | :---: | :---: | :---: | :---: | :---: |
| *(Likely Zinc)* | 30 | 70 | 30 | 30 | 40 | Zn |
| Cadmium | 48 | *(Varies, e.g., 112)* | 48 | 48 | *(e.g., 64)* | Cd |
| Mercury | 80 | *(Varies, e.g., 202)* | 80 | 80 | *(e.g., 122)* | Hg |
| Bromine | 35 | *(Varies, e.g., 79)* | 35 | 35 | *(e.g., 44)* | Br |

2. Identify the neutral atom
i) Hydrogen-3 (or Tritium)
ii) Chlorine-35
iii) Carbon-14

Part B: Isotope

1. Table Completion

| Symbol | # of protons | # of neutrons | # of electrons |
| :--- | :---: | :---: | :---: |
| $^1H_1$ | 1 | 0 | 1 |
| $^2H_1$ | 1 | 1 | 1 |
| $^4He_2$ | 2 | 2 | 2 |
| $^5He_2$ | 2 | 3 | 2 |
| $^6Li_3$ | 3 | 3 | 3 |
| $^7Li_3$ | 3 | 4 | 3 |

| Symbol | # of protons | # of neutrons | # of electrons |
| :--- | :---: | :---: | :---: |
| $^{17}O_8$ | 8 | 9 | 8 |
| $^{39}K_{19}$ | 19 | 20 | 19 |
| $^{40}Ca_{20}$ | 20 | 20 | 20 |
| $^{235}U_{92}$ | 92 | 143 | 92 |
| $^{244}Pu_{94}$ | 94 | 150 | 94 |
| $^{56}Fe_{26}^{3+}$ | 26 | 30 | 23 |