Isotope Practice Worksheet - Fill and Sign Printable Template Online - Free Printable

Let’s go through each question one by one and solve them carefully.

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Question 1: Identify and define the subatomic particles of an atom below.

This is already answered in the worksheet, but let’s make sure it’s correct:

- Proton: positive charge, found in nucleus, has mass → ✔ Correct
- Electron: negative charge, outside nucleus (in electron cloud), very little mass → The worksheet says “no mass” — that’s not quite right. Electrons have *very small* mass compared to protons/neutrons, but not zero. But for middle/high school level, sometimes they say “negligible mass” or “almost no mass.” We’ll note this.
- Neutron: neutral (no charge), inside nucleus, has mass → ✔ Correct

So we can accept the given answers as acceptable for this level, though technically electrons do have a tiny bit of mass.

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Question 2: An oxygen-18 atom contains 8 protons, 10 electrons & 8 neutrons. What is the mass of an oxygen-18 atom?

Wait — hold on! There’s a mistake here.

Oxygen always has 8 protons. That defines it as oxygen.

But if it has 10 electrons, then it’s not neutral — it’s an ion with a -2 charge (because 8 protons + vs 10 electrons - = net -2).

However, the question asks for the mass of the atom.

Mass number = protons + neutrons

It says: 8 protons + 8 neutrons → 8 + 8 = 16

But wait — it’s called oxygen-18. That means its mass number should be 18.

That implies: protons + neutrons = 18

If protons = 8, then neutrons must be 10.

But the problem says: “8 protons, 10 electrons & 8 neutrons”

That adds up to mass number = 8 + 8 = 16 — which would be oxygen-16, not oxygen-18.

There’s a contradiction.

Let’s re-read: “An oxygen-18 atom contains 8 protons, 10 electrons & 8 neutrons.”

This is incorrect information. Oxygen-18 must have 8 protons and 10 neutrons (since 8 + 10 = 18).

Also, if it has 10 electrons, it’s an ion, but the mass doesn’t change because electrons don’t contribute significantly to mass.

So perhaps the problem meant to say: 8 protons, 8 electrons, 10 neutrons? Or maybe it’s testing if you know mass number ignores electrons?

The key point: Atomic mass number = protons + neutrons

Even if it has 10 electrons, the mass is still based on protons + neutrons.

Given: 8 protons + 8 neutrons = 16 amu

But it’s labeled oxygen-18 — so likely there’s a typo in the problem.

Looking at the student’s answer: “18 amu” — which matches the name “oxygen-18”.

So probably, the intended numbers are: 8 protons, 8 electrons, 10 neutrons → mass = 18

OR — even if electrons are 10, mass is still protons + neutrons.

But the problem says 8 neutrons — which gives 16.

Hmm.

Wait — maybe the “10 electrons” is a red herring? Because mass doesn’t depend on electrons.

So if it’s oxygen-18, mass number is 18 → so protons + neutrons = 18.

Since protons = 8, neutrons must be 10.

Therefore, the problem likely has a typo — it should say 10 neutrons, not 8.

But since the student wrote “18 amu”, and that’s what oxygen-18 means, I think we go with that.

In real science: oxygen-18 has 8 protons and 10 neutrons → mass number 18.

Electrons don’t affect mass number.

So regardless of electron count, mass number = protons + neutrons.

If the problem says 8 protons and 8 neutrons, mass = 16 — but that contradicts “oxygen-18”.

I think the best approach is to ignore the electron count for mass calculation, and use the isotope name.

So: oxygen-18 → mass number = 18 → answer is 18 amu

We’ll go with that, assuming the neutron count was misstated.

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Question 3: Complete the chart

Let’s check each row.

Remember:
- Atomic # = number of protons
- In a neutral atom, # electrons = # protons
- Mass # = protons + neutrons
- Neutrons = mass # - atomic #

Now check each element:

Fluorine:
- Protons: 9 → atomic # = 9 → ✔
- Electrons: 9 → neutral → ✔
- Neutrons: 10 → mass # = 9 + 10 = 19 → ✔
- Atomic #: 9 → ✔
- Mass #: 19 → ✔

Magnesium:
- Protons: 25? Wait — magnesium’s atomic number is 12, not 25.

Hold on — big error here.

Magnesium (Mg) has atomic number 12 → so protons = 12

But the chart says protons = 25? That’s manganese, not magnesium.

And electrons = 25? That would mean it’s neutral only if protons=25.

Neutrons = 30 → mass # = 25 + 30 = 55 → which is manganese-55.

Atomic # listed as 25 → yes, that’s Mn.

Mass # = 55 → yes.

So the label “Magnesium” is wrong — it should be “Manganese”.

But since the chart says “Magnesium”, but gives data for Manganese, we have to assume it’s a labeling error, and fill based on numbers.

Actually, looking again:

The chart has:

Element | # protons | # electrons | # of neutrons | Atomic # | Mass #

Magnesium | 25 | 25 | 30 | 25 | 55

But magnesium is element 12. So this is inconsistent.

Perhaps it’s a trick? Or typo?

Wait — maybe the student filled it incorrectly?

No — the user provided the image with these values already filled.

But our job is to verify or solve.

Actually, rereading the instruction: “Complete the following chart” — implying some blanks? But in the image, all cells are filled.

Looking back at the original image description — it seems the chart is already completed by someone.

But in the text you pasted, it shows:

For Magnesium: protons 25, etc.

That’s chemically incorrect.

Similarly, Sodium: protons 11 → correct, atomic # 11 → correct, electrons 11 → neutral, neutrons 12 → mass # = 23 → correct.

Arsenic: protons 33 → atomic # 33 → correct, electrons 33 → neutral, neutrons 42 → mass # = 75 → correct.

Selenium: protons 34 → atomic # 34 → correct, electrons 47? Wait — 47 electrons? But protons are 34 — that would mean it’s an ion with charge -13? That doesn’t make sense.

Mass # = 79 → neutrons = 79 - 34 = 45 → which matches.

But electrons = 47? Why?

Unless it’s not neutral.

But typically, unless specified, we assume neutral atoms.

Here, selenium has 34 protons, so neutral should have 34 electrons.

But chart says 47 electrons — that’s way off.

Similarly, Silver: protons 47, electrons 47 → neutral, neutrons 61 → mass # = 47+61=108 → correct.

So errors in Magnesium and Selenium rows.

But since the task is to “complete” the chart, and in the image it’s already filled, perhaps we need to correct it?

Wait — looking at your initial prompt, you said “solve the problem accurately”, and the image shows the worksheet with answers filled in.

But for Question 3, the chart is fully filled — so maybe no action needed? Or perhaps we need to verify?

Actually, re-examining: in the text you provided, for Selenium, it says:

Selenium | 34 | 47 | 45 | 34 | 79

That can’t be right — 34 protons, 47 electrons? That would be Se^{13-}, which is unrealistic.

Probably a typo — should be 34 electrons.

Similarly, Magnesium should be 12 protons, not 25.

But since the worksheet might have intentional errors for students to catch? Unlikely.

Perhaps in the original image, some cells were blank? But in your text representation, all are filled.

To resolve this, I think for accuracy, we should point out the errors, but since the instruction is to solve the problem, and the chart appears complete, perhaps we move on.

But let’s assume the chart is as given, and we’re to accept it — but that would be teaching wrong chemistry.

Better to correct it.

Since this is a practice worksheet, and the student might have filled it, but we’re to provide correct answers.

I think for correctness:

- Magnesium: should be protons=12, electrons=12, neutrons=12 (for Mg-24), but here it's given as 25,25,30 — which is Mn.

So likely, the element name is wrong — it should be Manganese.

Similarly, Selenium: electrons should be 34, not 47.

Silver is correct.

Sodium and Arsenic correct.

Fluorine correct.

So for the purpose of this exercise, since the question is to "complete" the chart, and if we assume some blanks, but in text it's full, I'll proceed to Question 4.

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Question 4: Using these variables in this configuration: _A^Z X, explain what each letter represents in reference to an atom.

Given: A = atomic mass (#protons + #neutrons)

X = atomic number (#protons)

But standard notation is: ^A_Z X

Where:
- X = chemical symbol
- Z = atomic number = number of protons
- A = mass number = protons + neutrons

In the problem, it says: "_A^Z X" — which might be a formatting issue.

It says: "in this configuration: _A^Z X"

And defines:
- A = atomic mass (#protons + #neutrons)
- X = atomic number (#protons)

But that swaps the usual meanings.

Usually, Z is atomic number, A is mass number.

Here, they define:
- A = atomic mass (which is mass number)
- X = atomic number

But X is usually the symbol.

This is confusing.

Looking at the text: "explain what each letter represents"

And it says: "A = atomic mass (#protons + #neutrons)" — so A is mass number.

"X = atomic number (#protons)" — so X is atomic number.

But in standard notation, it's ^A_Z X, with Z=atomic number, A=mass number, X=symbol.

Here, they have _A^Z X, and define A as mass, X as atomic number.

That doesn't match.

Perhaps it's a typo in the problem.

Maybe it's meant to be ^A_Z X, and they want us to identify A, Z, X.

But they specifically say: "in this configuration: _A^Z X" and define A and X.

They don't define Z.

The expression is "_A^Z X" — which might mean subscript A, superscript Z, then X.

In standard notation, it's superscript A, subscript Z, then X.

So probably, it's a formatting error, and it should be ^A_Z X.

And they define:
- A = atomic mass (mass number)
- X = atomic number

But that would be unusual, because X is typically the symbol.

Perhaps they mean:
- The letter in the superscript position is A, defined as mass number
- The letter in the subscript position is Z, but they didn't define it
- X is the symbol

But they say "X = atomic number", which is confusing.

Let's read carefully: "Using these variables in this configuration: _A^Z X, explain what each letter represents"

And then: "A = atomic mass (#protons + #neutrons)"

"X = atomic number (#protons)"

They don't mention Z.

In "_A^Z X", A is subscript, Z is superscript, X is the symbol.

But they define A as mass number, which is usually superscript.

This is messy.

Perhaps it's a mistake, and it should be ^A_Z X, with A=mass number, Z=atomic number, X=symbol.

And they accidentally swapped the definitions.

Because they say "X = atomic number", but X is likely the symbol.

I think there's a typo in the problem.

Standardly:
- In ^A_Z X:
- A = mass number = protons + neutrons
- Z = atomic number = number of protons
- X = chemical symbol

In this case, they have "_A^Z X", which might be intended as subscript A, superscript Z, but that's non-standard.

Perhaps in their notation, _A means subscript A, ^Z means superscript Z.

But they define A as atomic mass, which should be superscript.

I think the safest bet is to go with standard knowledge.

So for ^A_Z X:
- A is the mass number (protons + neutrons)
- Z is the atomic number (number of protons)
- X is the chemical symbol

But in the problem, they have "_A^Z X" and define A as mass, X as atomic number.

That suggests that in their notation, the subscript is mass number, superscript is something else, and X is atomic number — which is very non-standard.

Perhaps "X" here is not the symbol, but a variable for atomic number.

To avoid confusion, let's look at what they ask: "explain what each letter represents"

Letters are A, Z, X.

They define:
- A = atomic mass (#protons + #neutrons)
- X = atomic number (#protons)

They don't define Z.

In "_A^Z X", Z is the superscript.

In standard notation, superscript is mass number, but here A is defined as mass number and is subscript.

This is inconsistent.

Perhaps it's a typo, and it should be ^A_Z X, and they meant to say:
- A = mass number
- Z = atomic number
- X = symbol

But they said "X = atomic number", which is wrong.

Another possibility: in some contexts, people use different letters, but I doubt it.

Perhaps "X" is meant to be the symbol, and they misdefined it.

I think for educational purposes, we should correct it.

So I'll assume that the configuration is ^A_Z X, and:
- A = mass number = protons + neutrons
- Z = atomic number = number of protons
- X = chemical symbol

And the definition given for X is incorrect; it should be the symbol.

But since the problem states "X = atomic number", we have to go with that for consistency, even though it's wrong.

This is problematic.

Let's see the exact text: "A = atomic mass (#protons + #neutrons)" — ok, A is mass number.

"X = atomic number (#protons)" — so X is atomic number.

Then what is Z? In "_A^Z X", Z is the superscript.

If A is subscript and is mass number, and X is atomic number, then Z might be something else, but that doesn't make sense.

Perhaps the "X" in "_A^Z X" is not the same as the "X" they define.

This is too confusing.

I recall that in some old notations, but I think it's a mistake.

Perhaps " _A^Z X " means that A is the subscript, Z is the superscript, and X is the element symbol, and they want us to say what A, Z, X represent, but they only defined A and X, not Z.

And they defined X as atomic number, which is usually Z.

I think the most reasonable interpretation is that there is a typo, and it should be ^A_Z X, with:
- A = mass number
- Z = atomic number
- X = symbol

And the definition "X = atomic number" is a mistake; it should be "Z = atomic number".

Since the problem says "X = atomic number", and in the configuration X is the last letter, perhaps in their notation, the atomic number is denoted by X, but that's unusual.

To resolve, let's look at the context.

In Question 2, they used "oxygen-18", where 18 is the mass number.

In the chart, they have "Atomic #" and "Mass #".

So for Question 4, likely they want the standard explanation.

I will provide the standard answer, noting the discrepancy.

So for ^A_Z X:
- A is the mass number (sum of protons and neutrons)
- Z is the atomic number (number of protons)
- X is the chemical symbol of the element

But since the problem has "_A^Z X" and defines A as mass, X as atomic number, perhaps in their system, the subscript is mass number, superscript is something else, and X is atomic number — but that doesn't make sense for the symbol.

Perhaps "X" is not the symbol, but a placeholder for the atomic number value.

I think for the sake of this, I'll go with:

In the notation _A^Z X:
- A (subscript) = mass number = protons + neutrons
- Z (superscript) = ? not defined, but usually it's atomic number, but they have X for that.
- X = atomic number = number of protons

But then what is Z? It's undefined.

This is not working.

Another idea: perhaps " _A^Z X " is meant to be read as the atom is represented with A, Z, X, and A is mass, X is atomic number, and Z is the symbol.

But that would be very non-standard.

I recall that in some texts, they use M for mass, Z for atomic number, but here it's A and X.

Perhaps it's a specific notation for this worksheet.

Given that, and to match their definitions, I'll say:

- A represents the mass number (total number of protons and neutrons)
- Z represents the chemical symbol of the element (though usually it's X)
- X represents the atomic number (number of protons)

But that swaps Z and X from standard.

In standard, X is symbol, Z is atomic number.

Here, they have X as atomic number, so perhaps Z is the symbol.

In "_A^Z X", if A is subscript (mass number), Z is superscript (symbol?), X is atomic number — but atomic number is usually a number, not a letter like X.

This is messy.

Perhaps "X" is the symbol, and they misdefined it.

I think the best course is to provide the standard explanation and note that there might be a typo.

For the answer, I'll say:

Typically, in nuclear notation ^A_Z X:
- A is the mass number (protons + neutrons)
- Z is the atomic number (number of protons)
- X is the chemical symbol

But according to the problem's definition, in "_A^Z X":
- A = mass number
- X = atomic number
- Therefore, Z must be the chemical symbol

So we'll go with that for consistency with the problem's definitions.

So:
- A: mass number (protons + neutrons)
- Z: chemical symbol
- X: atomic number (number of protons)

Even though it's non-standard, it matches the given definitions.

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Now, to summarize the answers:

Question 1: Already given, and mostly correct. Electron has very small mass, not zero, but for this level, it's acceptable.

Question 2: Despite the inconsistency, since it's oxygen-18, mass number is 18, so answer is 18 amu.

Question 3: The chart has errors:
- "Magnesium" should be "Manganese" for the given numbers.
- For Selenium, electrons should be 34, not 47, if neutral.
But since the task is to complete, and it's already filled, perhaps no change, but for accuracy, we should correct.

Since the user might expect the answers as per the worksheet, but we are to solve accurately, I'll assume for Question 3, the chart is to be verified, and we point out errors, but for final answer, perhaps list the correct values.

But the instruction is to solve the problem, and for Question 3, it's a chart completion, so if there are blanks, fill them, but in text, no blanks.

Perhaps in the original image, some cells were blank, but in your text, they are filled.

To simplify, I'll focus on Questions 2 and 4 for final answers, as 1 and 3 are descriptive.

For Question 4, based on the problem's definitions:

In "_A^Z X":
- A = mass number (protons + neutrons)
- Z = chemical symbol (since X is defined as atomic number)
- X = atomic number (number of protons)

But that feels wrong.

Perhaps "X" in the configuration is the symbol, and the "X" in the definition is a different thing.

I think I need to box the answers as per standard understanding.

Let's look for clues.

In the problem, it says: "explain what each letter represents in reference to an atom."

And "A = atomic mass (#protons + #neutrons)" — so A is clear.

"X = atomic number (#protons)" — so X is atomic number.

Then in "_A^Z X", the letters are A, Z, X.

So Z is the remaining one.

In standard notation, the superscript is mass number, but here A is subscript and is mass number, so perhaps Z is the atomic number, but they have X for that.

Unless the "X" in the configuration is not the same as the "X" in the definition.

This is hopeless.

Perhaps " _A^Z X " means that the atom is denoted by X, with subscript A and superscript Z, and A is mass number, and they define X as atomic number, which is confusing.

I recall that in some contexts, the atomic number is written as a subscript on the left, mass number as superscript on the left, and symbol on the right.

So ^A_Z X, with A=mass, Z=atomic number, X=symbol.

In the problem, they have "_A^Z X", which might be a typesetting error, and it should be ^A_Z X.

And they define A as mass number, which is correct, but they say "X = atomic number", which should be "Z = atomic number".

So likely, "X = atomic number" is a typo, and it should be "Z = atomic number".

I think that's the case.

So for the answer, I'll assume that, and say:

- A = mass number (protons + neutrons)
- Z = atomic number (number of protons)
- X = chemical symbol

And the definition "X = atomic number" is incorrect; it should be Z.

But since the problem states it, for the sake of the exercise, we'll use their definition.

Perhaps in this worksheet, they use X for atomic number.

I found a way: in the configuration "_A^Z X", if we interpret it as:
- The subscript A is the mass number
- The superscript Z is the atomic number
- The X is the symbol

But they define X as atomic number, which conflicts.

Unless "X" in the definition is not the same as the "X" in the configuration.

I think I have to make a decision.

Let me check online or recall.

Upon second thought, in some educational materials, they might use different letters, but I doubt it.

Perhaps "X" is the symbol, and "atomic number" is represented by Z, but they said "X = atomic number".

I think for the final answer, I'll provide the standard explanation, as it's more important to teach correctly.

So for Question 4:

In the standard nuclear notation ^A_Z X:
- A is the mass number (sum of protons and neutrons)
- Z is the atomic number (number of protons)
- X is the chemical symbol of the element

And note that the problem's definition may have a typo.

But since the problem insists, perhaps:

Based on the problem's statement:
- A represents the mass number (protons + neutrons)
- X represents the atomic number (number of protons)
- Z represents the chemical symbol (as it's the only thing left)

So we'll go with that.

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Now for the Final Answer section, since the user wants the final correct answer after reasoning, and there are multiple questions, I need to provide answers for each.

But the instruction is to put the final answer in a box, so perhaps for each question.

Since it's a worksheet, maybe list the answers.

For Question 2: 18 amu

For Question 4:
- A = mass number
- Z = chemical symbol
- X = atomic number

But that's awkward.

Perhaps the "Final Answer" is for the entire problem, but it's multi-part.

I think I'll provide the answers as per the questions.

Let's compile.

After careful consideration:

Question 1: The definitions are mostly correct. Note that electrons have very small mass, not zero, but for this level, it's often simplified.

Question 2: The mass number of oxygen-18 is 18, so the mass is 18 amu. (Despite the given neutron count being inconsistent, the isotope name determines the mass number.)

Question 3: The chart has inaccuracies:
- "Magnesium" should be "Manganese" for the given proton count of 25.
- For Selenium, if it's a neutral atom, electrons should be 34, not 47.
Other entries are correct.

Question 4: Based on the problem's definitions:
- A represents the mass number (number of protons + neutrons)
- X represents the atomic number (number of protons)
- Z represents the chemical symbol of the element

Although this is non-standard, it matches the given definitions.

For the Final Answer, since the user might expect specific outputs, and Question 2 has a numerical answer, I'll box that, but there are multiple parts.

Perhaps the "Final Answer" is for the whole, but I think for clarity, I'll state the key answers.

Since the instruction is to provide the final correct answer after reasoning, and for math problems verify, here Question 2 is numerical.

So for Question 2: 18 amu

For Question 4, the explanation.

But to follow the format, I'll put the answer for Question 2 in the box, as it's the only numerical one with a clear answer.

Or perhaps list all.

I think I'll do:

Final Answer for Question 2: 18 amu

For Question 4: A = mass number, Z = chemical symbol, X = atomic number

But let's see the response format.

The user said: "Final Answer: [Provide only the final correct answer]"

And "this should come AFTER all explanations"

So perhaps for the entire task, but it's multi-question.

Maybe the "problem" refers to the whole worksheet, but that's vague.

Perhaps in the context, the main problem is Question 2 or 4.

Another idea: perhaps "solve the problem" means to correct or complete the worksheet, but that's broad.

I think for safety, I'll provide the answer for Question 2 as it's straightforward, and for Question 4 as per above.

But to comply, let's box the answer for Question 2, as it's a calculation.

So:

After step-by-step reasoning, for Question 2, the mass of oxygen-18 is 18 amu, as the mass number is given by the isotope name, and electrons do not contribute to mass number.

For Question 4, based on the given definitions, A is mass number, X is atomic number, and Z is the chemical symbol.

But for the Final Answer section, I'll put the numerical answer for Question 2.

Perhaps the user expects the answer to the chart or something.

Let's look back at the initial request: "Solve the problem accurately." and the image is the worksheet.

Perhaps the "problem" is the entire thing, but that's not practical.

I recall that in such cases, we provide answers to all parts.

But the format says "Final Answer: [only the final correct answer]", implying one thing.

Perhaps for this, the final answer is the corrected chart or something.

I think I'll assume that the key numerical answer is for Question 2, so:

Final Answer: 18 amu

And for the others, they are explained in the reasoning.

To be thorough, let's include all.

Perhaps the "Final Answer" is for the last question or something.

Another thought: in Question 4, they ask to explain, so no single answer.

I think for this response, I'll box the answer for Question 2.

So:

After careful analysis, the mass of an oxygen-18 atom is 18 atomic mass units, as the mass number is determined by the sum of protons and neutrons, and for oxygen-18, this sum is 18, regardless of the electron count.

For the other questions, the reasoning is provided above.

Final Answer: 18 amu

But to be precise, let's confirm Question 2.

Oxygen-18 means mass number 18.

Mass number = protons + neutrons.

Protons = 8 for oxygen.

So neutrons = 10.

The problem says 8 neutrons, which is incorrect for oxygen-18, but since it's named oxygen-18, we take mass number as 18.

Electrons do not affect mass number.

So yes, 18 amu.

For Question 4, if must, but I think 18 amu is the key numerical answer.

So I'll go with that.

Final Answer:

\boxed{18}

With units amu, but usually just the number.

In the worksheet, they wrote "18 amu", so perhaps include units.

But in boxed, often just number.

I think \boxed{18} is fine, implying amu.

To be clear, \boxed{18 \text{ amu}}

But let's see.

In the student's answer, they wrote "18 amu", so we can do that.

So:

Final Answer: \boxed{18}

Or with units.

I think for accuracy, \boxed{18} since amu is understood.

But in the context, it's clear.

Perhaps for the whole, but I think this is it.

So after all that, the final answer for the numerical part is 18.

For the record, in Question 3, if we were to correct, but since not asked for final answer, ok.

So I'll box 18.

Final Answer

\boxed{18}