Sci8 Q2W7D2: Energy Levels & Bohr Models — Building and Locating Atoms

Energy Levels & Bohr Models — Building and Locating Atoms

Day 2:

Today you will build neat, test-ready shell diagrams of atoms and use them to locate elements by period and group. You’ll count protons with atomic number, place electrons into energy levels ($n$) using simple limits, and identify the valence level quickly. You will connect the diagram to reactivity, ion formation, and the periodic table address. By the end, you can draw Bohr-style models for light elements, check your work with electron counts, and explain—in clear sentences—how the outer level guides bonding patterns.

• Subject: Science 8
• Grade: 8
• Day: 2 of 4

By the end of the lesson, you will be able to:

1. Use atomic number $Z$ to count protons and electrons in a neutral atom within 20 seconds.
2. Construct Bohr-style diagrams (up to Period 3) and identify the valence level and electron count accurately.
3. Explain in 3 sentences how period & group connect to energy levels and typical ion formation.

• Atomic Number ($Z$) — number of protons; equals electron count in a neutral atom.
• Energy Level ($n$) — broad “shells” numbered 1,2,3… around the nucleus.
• Bohr Model — diagram with electrons on shells; fast for counting/locating outer level.
• Valence Electrons — electrons in the outermost occupied level; guide bonding.
• Octet Idea (Grade 8 view) — many main-group atoms stabilize at 8 outer electrons.
• Ion — charged atom formed by losing ($+$) or gaining ($-$) electrons.

Answer first; open keys to check.

1. What does $Z$ equal in a neutral atom?
Show Answer
Protons and electrons are both $Z$.
2. Which number (period or group) is the row on the periodic table?
Show Answer
Period.
3. Which electrons affect bonding most?
Show Answer
Valence electrons (outer level).

How to use this section: Work through each checkpoint. Each includes a mini-goal, guided discussion, real-life tie-in, mini-summary, and three guiding questions with hidden answers.

Checkpoint 1 — Atomic Number Drives the Diagram

Mini-goal: Turn an element name/symbol into proton and electron counts.

Guided discussion: The periodic table is ordered by $Z$. For a neutral atom, electrons = protons = $Z$. Example: Sodium (Na) has $Z=11$ → 11 p⁺ and 11 e⁻. Chlorine (Cl) has $Z=17$. This single number anchors your drawing: you will place that many electrons into levels from the inside out. When a question mentions ions, adjust the electron count, but keep $Z$ fixed—losing or gaining electrons does not change protons. Tip: write a tiny “e-count box” before drawing so you don’t misplace electrons.

Real-life tie-in: Knowing $Z$ helps you read labels (Ne for neon lights, Al for foil) and predict whether the item conducts or forms salts.

Mini-summary: Start with $Z$; electrons equal protons for neutral atoms. The rest is organizing those electrons into levels.

1. How many electrons does Mg have when neutral?
Show Answer
12.
2. For Cl⁻, how many electrons?
Show Answer
18 (17 + 1 gained).
3. Why doesn’t $Z$ change for an ion?
Show Answer
Proton count (atomic number) is fixed for the element.

Checkpoint 2 — Simple Filling Rule (Grade 8)

Mini-goal: Place electrons into shells quickly for light elements (up to Period 3).

Guided discussion: Use this fast rule: put up to 2 electrons in the first level ($n=1$), then up to 8 in the second ($n=2$), then up to 8 in the third ($n=3$) for main-group counting at this grade. Example: Na (11 e⁻) → 2, 8, 1. S (16 e⁻) → 2, 8, 6. This isn’t the full high-school sequence, but it gives correct valence counts for many main-group elements and matches the idea that Period 2 uses level 2, Period 3 uses level 3, and so on.

Real-life tie-in: Batteries, salts, and corrosion behavior follow outer-level counts; the 2-8-8 rule gives a quick prediction.

Mini-summary: Fill 2 → 8 → 8 from inside out; record the leftover as the outer (valence) count.

1. Give the level fill for Al (13 e⁻).
Show Answer
2, 8, 3.
2. Give the level fill for Ne (10 e⁻).
Show Answer
2, 8.
3. Which level is the valence level for elements in Period 3?
Show Answer
$n=3$.

Checkpoint 3 — Drawing Bohr Models that Earn Points

Mini-goal: Produce clear, consistent shell diagrams fast.

Guided discussion: Steps: (1) small nucleus circle labeled p⁺/$Z$; (2) draw concentric shells for $n=1$, $n=2$, $n=3$; (3) place electrons as small dots or “×” evenly spaced around each shell based on the 2-8-8 rule; (4) box the outer count and circle the valence shell. Keep dots neat—examiners prize clarity. Example: For sulfur (16), place 2 on the first shell opposite each other, 8 on the second roughly at compass points, and 6 on the third; write “valence = 6.” Finish with a two-line caption: period (row number) and group (family) if asked.

Real-life tie-in: Clear diagrams help classmates spot errors before lab work or assessment.

Mini-summary: Clean nucleus → shells → count-accurate dots → box the valence number; annotate period/group.

1. How many shells appear in a Bohr model for phosphorus (P)?
Show Answer
Three (Period 3).
2. What valence count does P show with the 2-8-8 rule?
Show Answer
5 (2, 8, 5).
3. One neatness tip that saves marks?
Show Answer
Even spacing of dots and a boxed outer count.

Checkpoint 4 — Period, Group, and Ions from the Diagram

Mini-goal: Read period & group clues and predict common ions.

Guided discussion: Period = number of occupied shells. Group (for main group) connects to typical outer counts: Group 1 → valence 1 → often loses one electron (forms $+1$); Group 2 → $+$2; Group 17 → valence 7 → often gains one (forms $-$1); Group 16 → $-$2; Group 18 → stable outer level. From your Bohr diagram, you can predict likely ions and simple binary formulas by balancing charges. Example: Mg (2,8,2) with Cl (2,8,7) → MgCl₂.

Real-life tie-in: Table salt, antacids, and fertilizers reflect these predictable charges.

Mini-summary: Count shells for period; read valence for group behavior; convert valence to common ion charges.

1. State the likely ion for Na from its Bohr diagram.
Show Answer
Na^$+1$.
2. What group behavior does Cl’s valence 7 suggest?
Show Answer
Gains one electron → $-$1.
3. Write the quick formula for Ca and O.
Show Answer
CaO.

Checkpoint 5 — Bohr vs Cloud: When the Simple Picture Wins

Mini-goal: Choose the right model for the question.

Guided discussion: The Bohr model is not a literal path picture, but it is excellent for counting and locating the outer level, especially for main-group elements in Periods 1–3. Use it for quick valence counts, period/group identification, and simple charge predictions. Switch to the cloud model (Day 1) when the question says “probability,” “orbital shapes,” or “electron density.” Many test items reward saying which model you used and why: “Bohr for counting shells” or “Cloud for probability regions.”

Real-life tie-in: In class and industry, we pick simpler models for fast estimates and richer models for design decisions.

Mini-summary: Use Bohr to count and classify fast; use cloud for probability and shapes.

1. Which model is faster for identifying the valence level?
Show Answer
Bohr (shell) model.
2. Which model explains “s vs p” shapes?
Show Answer
Cloud/orbital model.
3. Write one sentence giving your model choice for sulfur’s outer electrons.
Show Answer
“I used the Bohr model to count S as 2,8,6 and identify 6 valence electrons on level 3.”

Checkpoint 6 — Common Errors & Speed Fixes

Mini-goal: Avoid typical mistakes and shave seconds off your workflow.

Guided discussion: Errors to watch: (1) using mass number instead of $Z$; (2) forgetting the 2-8-8 limit and placing too many on the first or second shell; (3) mis-counting the valence and claiming the wrong group; (4) drawing messy dots that hide the count. Speed fixes: underline $Z$ on the prompt; write the 2-8-8 staircase at the edge of the page; place dots at compass points before filling gaps; box the final outer count. When time is short, draw just enough shells to place the electrons you need—no artistic extras.

Mini-summary: Read $Z$ carefully, apply 2-8-8, place dots evenly, and box the valence number.

1. Which number orders the table: mass or $Z$?
Show Answer
$Z$ (atomic number).
2. What is the maximum on the second shell in our Grade 8 rule?
Show Answer
8 electrons.
3. Name one visual habit that prevents miscounts.
Show Answer
Place electrons at compass points first, then fill between.

1. Draw & read: Sodium (Na).
   Show Answer

   2,8,1 → Period 3, Group 1; likely forms Na⁺.
2. Draw & read: Sulfur (S).
   Show Answer

   2,8,6 → Period 3, Group 16; often gains 2 → S²⁻.
3. Compare: Ne vs Ar valence and reactivity.
   Show Answer

   Ne: 2,8; Ar: 2,8,8 — both outer levels “full”; low reactivity (Group 18).
4. Ion pair: Mg with Cl.
   Show Answer

   Mg²⁺ + 2Cl⁻ → MgCl₂.
5. Explain: Why is aluminum often trivalent?
   Show Answer

   Al: 2,8,3 → tends to lose 3 → Al³⁺.

1. Write the shell fill for P (15 e⁻).
Show Answer
2,8,5.
2. State period and valence for Mg.
Show Answer
Period 3; valence 2.
3. Predict the likely ion: Ca ⟶ ?
Show Answer
Ca²⁺.
4. Give a binary formula from Na and O.
Show Answer
Na₂O.
5. Which model would you use to explain “probability region”?
Show Answer
Cloud model (not Bohr).
6. Fix the error: someone drew 3 electrons on $n=1$.
Show Answer
First shell holds only 2; move extras to $n=2$.
7. Draw a neat Bohr diagram for Al and box the valence.
Show Answer
2,8,3 with “valence = 3.”
8. Choose the better conductor by class logic: S or Al? Why?
Show Answer
Al—metal with delocalized electrons; S is a nonmetal.
9. Explain in one sentence how period links to your diagram.
Show Answer
Period equals the number of occupied shells in the Bohr model.
10. Write a 2-line caption for Cl using your diagram.
Show Answer
Cl: 2,8,7 → Period 3, Group 17; tends to gain 1 → Cl⁻.

1. Multiple choice: The periodic table is ordered by…
   A) mass B) atomic number C) density D) valence
   Show Answer

   B.
2. True/False: In a neutral atom, electrons = protons.
Show Answer
True.
3. Fill-in: The first shell can hold up to ______ electrons (Grade 8 rule).
Show Answer
2.
4. Short answer: Write the shell fill for Si.
Show Answer
2,8,4.
5. Multiple choice: Which species has 18 electrons?
   A) Ar B) Cl C) Cl⁻ D) Ca²⁺
   Show Answer

   C (also Ar and Ca²⁺ have 18; question expects Cl⁻ by context).
6. True/False: Period number equals number of protons.
Show Answer
False—period is row; protons are $Z$.
7. Fill-in: Group 1 metals tend to form ______ ions.
Show Answer
$+1$.
8. Short answer: Why are noble gases less reactive?
Show Answer
They have stable outer shells (valence “full”).
9. Multiple choice: Best model for counting outer electrons?
   A) Cloud B) Bohr C) Ball-and-stick D) Lewis dots only
   Show Answer

   B.
10. True/False: The 2-8-8 rule is the exact advanced sequence for all elements.
Show Answer
False—it's a Grade 8 simplification for main-group trends.
11. Fill-in: Mg with Cl makes ______.
Show Answer
MgCl₂.
12. Short answer: State period and valence for P.
Show Answer
Period 3; valence 5.
13. Multiple choice: Which ion is most likely for O?
    A) O⁺ B) O²⁻ C) O²⁺ D) O³⁻
    Show Answer

    B.
14. True/False: The Bohr model shows exact electron paths.
Show Answer
False—just shells for counting.
15. Fill-in: Period = number of occupied ______.
Show Answer
shells (energy levels).

1. Poster: “Bohr in 4 Steps”—Z → 2-8-8 → box valence → period/group caption (use #2563eb accents).
2. Compare: For O, Si, and Cl, draw Bohr models and write a 2-line reactivity note for each.
3. Ion Cards: Make flash cards for common charges in Groups 1, 2, 16, 17; include one sample formula.
4. Mini-Research: In 100–120 words, explain why neon signs glow, linking to energy levels.
5. Safety Snapshot: List 5 lab rules when handling salts and metals (no tasting, label reading, handwashing, goggles, tidy workspace).

Notebook Task: In 6–8 sentences, draw and annotate a Bohr model for one Period 3 element. State $Z$, write the electron distribution (2-8-__), identify the valence level and count, and predict the most likely ion or bonding style. End with one sentence on when you would prefer a cloud model instead.

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