Formula practice worksheet for learning chemical formulas and valence electrons.

Let’s solve this step by step.

We are given a table with compounds and asked to:
1. Identify each element in the compound.
2. Fill in how many atoms of each element are present (based on subscripts).
3. Then, for the second part, we’re given elements and their valences, and we must write the correct chemical formula by balancing charges so the total charge is zero.

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Part 1: “What’s in it?” — Counting Atoms in Compounds

We go row by row.

Example given: H₂SO₄ → 2-Hydrogen, 1-Sulfur, 4-Oxygen

Now let’s do the rest:

#### 1. CO₂
- C = Carbon → subscript 1 (implied)
- O = Oxygen → subscript 2
→ 1-Carbon, 2-Oxygen

#### 2. PbO
- Pb = Lead → subscript 1
- O = Oxygen → subscript 1
→ 1-Lead, 1-Oxygen

#### 3. NaCl
- Na = Sodium → 1
- Cl = Chlorine → 1
→ 1-Sodium, 1-Chlorine

#### 4. BaF₂
- Ba = Barium → 1
- F = Fluorine → 2
→ 1-Barium, 2-Fluorine

#### 5. Fe₂O₃
- Fe = Iron → 2
- O = Oxygen → 3
→ 2-Iron, 3-Oxygen

#### 6. KOH
This one has a polyatomic ion: OH⁻ (hydroxide). But we still count individual atoms.
- K = Potassium → 1
- O = Oxygen → 1
- H = Hydrogen → 1
→ 1-Potassium, 1-Oxygen, 1-Hydrogen

#### 7. Na₂CO₃
Polyatomic ion: CO₃²⁻ (carbonate)
But again, count atoms:
- Na = Sodium → 2
- C = Carbon → 1
- O = Oxygen → 3
→ 2-Sodium, 1-Carbon, 3-Oxygen

#### 8. CaCl₂
- Ca = Calcium → 1
- Cl = Chlorine → 2
→ 1-Calcium, 2-Chlorine

#### 9. CH₄
- C = Carbon → 1
- H = Hydrogen → 4
→ 1-Carbon, 4-Hydrogen

#### 10. Ca₃(PO₄)₂
This has parentheses! The subscript outside applies to everything inside.
Inside PO₄: P=1, O=4 → multiplied by 2 → P=2, O=8
Plus Ca₃ → Ca=3
So:
- Ca = Calcium → 3
- P = Phosphorus → 2
- O = Oxygen → 8
→ 3-Calcium, 2-Phosphorus, 8-Oxygen

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Part 2: “Write Chemical Formula” — Using Valences

Rule: Total positive charge must equal total negative charge → net charge = 0.

We’ll use criss-cross method or find least common multiple to balance.

Given:

| Element | Valence # | Element | Valence # | Chemical Formula |
|---------|-----------|---------|-----------|------------------|
| Li | +1 | O | -2 | ? |
| H | +1 | S | -2 | ? |
| Ca | +2 | O | -2 | ? |
| Be | +2 | O | -2 | ? |
| Al | +3 | O | -2 | ? |
| B | +3 | I | -1 | ? |
| N | +3 | O | -2 | ? |
| Si | +4 | O | -2 | ? |
| Sn | +4 | Cl | -1 | ? |
| Ni | +2 | m | ? | ← Wait, “m” is not an element. Probably typo? Let’s assume it’s meant to be “S” or something else? But looking at pattern, maybe “m” is mistake. Since no info, skip or flag. Actually, looking back — last row says “Ni +2” and “m ???”. That doesn’t make sense. Maybe it’s “O”? Or perhaps “Cl”? But since it’s written as “m”, and no valence given, we can’t solve that one. Perhaps it’s a typo for “O” (-2)? Let’s assume it’s “O” for now, but note uncertainty. Alternatively, maybe “m” stands for “metal”? No — better to leave blank or mark error. But since this is homework help, let’s check original image context — wait, user said don’t describe image. So based on text provided: “Ni +2” and “m ???” — invalid. We’ll skip or assume typo. For safety, I’ll assume “m” was meant to be “O” (-2), as most common. But actually, looking at pattern, previous rows have non-metals. Maybe “m” is “S”? Still unknown. Best to omit or state issue. However, since instruction is to solve accurately, and “m” is not defined, we cannot complete that row. But let’s proceed with others first.

Actually, re-examining: In the table, last row is:

> Ni +2 m ???

That’s likely a typo. Possibly “O” or “Cl”. Given Ni commonly forms NiO or NiCl₂. Since valence of Ni is +2, if “m” is O (-2), then formula is NiO. If “m” is Cl (-1), then NiCl₂. But without knowing what “m” is, we can’t say. However, in many such worksheets, “m” might be a misprint for “O”. Let’s assume “m” = O (-2) for completion. But strictly speaking, it’s undefined. Since the problem says “fill in the blanks”, and “m” has no valence listed, perhaps it’s intentional to test attention? Unlikely. More probably typo. I’ll proceed assuming “m” is “O” with valence -2, as it’s the most logical completion.

Alternatively, maybe “m” is “S”? Sulfur is often -2. Same result as O for Ni²⁺ → NiS.

But to be safe, let’s list all solvable ones and note the last one as ambiguous.

Let’s compute each:

#### 1. Li (+1) and O (-2)
Need to balance: LCM of 1 and 2 is 2.
→ 2 Li and 1 O²⁻ → Li₂O

#### 2. H (+1) and S (-2)
LCM of 1 and 2 is 2.
→ 2 H⁺ and 1 S² → H₂S

#### 3. Ca (+2) and O (-2)
Charges already balance: +2 and -2 → CaO

#### 4. Be (+2) and O (-2)
Same as above → BeO

#### 5. Al (+3) and O (-2)
LCM of 3 and 2 is 6.
→ 2 Al³⁺ = +6, 3 O² = -6 → Al₂O₃

#### 6. B (+3) and I (-1)
LCM of 3 and 1 is 3.
→ 1 B³ and 3 I⁻ → BI₃

#### 7. N (+3) and O (-2)
LCM of 3 and 2 is 6.
→ 2 N³ = +6, 3 O²⁻ = -6 → N₂O₃

#### 8. Si (+4) and O (-2)
LCM of 4 and 2 is 4.
→ 1 Si⁺ and 2 O²⁻ → SiO₂

#### 9. Sn (+4) and Cl (-1)
LCM of 4 and 1 is 4.
→ 1 Sn⁴⁺ and 4 Cl⁻ → SnCl₄

#### 10. Ni (+2) and m (?)
As discussed, if “m” is O (-2) → NiO
If “m” is Cl (-1) → NiCl₂
But since valence not given, and “m” is not standard, this row is problematic.

However, looking back at the original task description: “List the valence electrons... then write the correct chemical formula...”

In the table, for “m”, valence is blank (“???”). So we cannot determine unless assumed.

Given that all other pairs are clear, and this is likely a typo, and considering common compounds, Ni often pairs with O to form NiO. Also, in many textbooks, after SnCl₄, they might put NiO.

I will assume “m” is “O” with valence -2 for completion.

Thus: Ni (+2) and O (-2) → NiO

But to be accurate, since the problem didn’t specify, I should note that. However, per instructions, provide final answer only after reasoning. And since this is a worksheet, likely expected to fill all.

Alternative: Maybe “m” is “S”? Sulfur is also -2 → NiS. Same ratio.

Either way, formula would be NiX where X has -2 charge.

So NiO or NiS — both valid, but without specification, we pick most common: NiO.

Actually, nickel oxide is very common. Let’s go with NiO.

But wait — in the table, for oxygen, it’s always written as “O”, not “m”. So “m” is probably a different element. Could it be “Br”? Bromine is -1 → then NiBr₂. But again, not specified.

Given the ambiguity, and since the problem says “fill in the blanks”, and “m” has no valence, perhaps it’s a trick? Unlikely.

Another idea: Maybe “m” is a placeholder for “metal”? But that doesn’t make sense.

Looking at the sequence: Li,O; H,S; Ca,O; Be,O; Al,O; B,I; N,O; Si,O; Sn,Cl; Ni,m

Notice that “m” is lowercase — perhaps it’s “Mg”? But Mg is metal, valence +2, not negative. Doesn’t fit.

Perhaps it’s “P”? Phosphorus can be -3, but not matching.

I think the safest is to leave it as unsolvable, but since the worksheet expects an answer, and given Ni is +2, the most probable partner with unspecified valence is oxygen (-2), so NiO.

I’ll proceed with that.

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Now, compiling all answers.

Final Answer section should contain only the completed tables or lists.

Since the output format requires "Final Answer" to be the final correct answer, and there are two parts, I’ll present them clearly.

But per rules: “Provide only the final correct answer — this should come AFTER all explanations and reasoning.”

And since ExplainAnswer is false, TeachTopic false, GeneratePractice false, we only give Final Answer.

But what does “final answer” mean here? It’s a worksheet with multiple entries.

Probably, we need to list all filled values.

To keep it clean, I’ll write the answers in order.

For Part 1: “What’s in it?” — list for each compound the atom counts.

For Part 2: “Chemical Formula” — list the formulas.

Since it’s a table, perhaps present as:

Part 1 Answers:
CO₂: 1-Carbon, 2-Oxygen
PbO: 1-Lead, 1-Oxygen
NaCl: 1-Sodium, 1-Chlorine
BaF₂: 1-Barium, 2-Fluorine
Fe₂O₃: 2-Iron, 3-Oxygen
KOH: 1-Potassium, 1-Oxygen, 1-Hydrogen
Na₂CO₃: 2-Sodium, 1-Carbon, 3-Oxygen
CaCl₂: 1-Calcium, 2-Chlorine
CH₄: 1-Carbon, 4-Hydrogen
Ca₃(PO₄)₂: 3-Calcium, 2-Phosphorus, 8-Oxygen

Part 2 Answers:
Li and O: Li₂O
H and S: H₂S
Ca and O: CaO
Be and O: BeO
Al and O: Al₂O₃
B and I: BI₃
N and O: N₂O₃
Si and O: SiO₂
Sn and Cl: SnCl₄
Ni and m: [assuming m=O] NiO

But for Ni and m, since it's ambiguous, perhaps omit or note. But per instruction, provide final answer.

Given that, and to be precise, I'll include NiO with assumption.

Now, for the Final Answer box, since it's multiple items, I'll format as a list.

But the rule says "only the final correct answer", so perhaps concatenate or present neatly.

I think for clarity, I'll write:

Final Answer:
Part 1:
CO₂: 1-Carbon, 2-Oxygen
PbO: 1-Lead, 1-Oxygen
NaCl: 1-Sodium, 1-Chlorine
BaF₂: 1-Barium, 2-Fluorine
Fe₂O₃: 2-Iron, 3-Oxygen
KOH: 1-Potassium, 1-Oxygen, 1-Hydrogen
Na₂CO₃: 2-Sodium, 1-Carbon, 3-Oxygen
CaCl₂: 1-Calcium, 2-Chlorine
CH₄: 1-Carbon, 4-Hydrogen
Ca₃(PO₄)₂: 3-Calcium, 2-Phosphorus, 8-Oxygen

Part 2:
Li₂O, H₂S, CaO, BeO, Al₂O₃, BI₃, N₂O, SiO₂, SnCl₄, NiO (assuming "m" is oxygen with valence -2)

But to strictly follow, and since the last one is uncertain, perhaps the worksheet intends "m" to be something else. Another thought: in some contexts, "m" might stand for "chloride" but that's not standard.

Perhaps "m" is a typo for "Cl"? Then NiCl₂. But Sn was already paired with Cl.

Looking at the valence column for "m" is "???", so no info.

I recall that in some old worksheets, "m" might be used for "metal", but here it's in the element column.

Best to state the assumption.

Since the problem is from a student homework, and likely expects NiO, I'll go with that.

Final decision: Include NiO.

So, Final Answer as above.