Question
Electron Configuration and Periodic Properties — Lab 7 Report SheetPre-lab1. Why does a sodium street lamp emit yellow light while a neon light emits red light?2. Describe electron energy levels.3. Why do some elements produce colorful flames?4. How can a flame test identify an unknown element?5. Write the electron configurations of lithium, sodium, and potassium.6. Why do those three configurations end with the same sublevel pattern?A. Flame testsRecord the flame colors of CaCl2, KCl, BaCl2, SrCl2, CuCl2, and NaCl. Record the unknown letter, observed flame color, and element identified. Explain why salted spaghetti water boiling into a gas flame can make the flame bright orange.B. Electron configurationsFor O, Na, Ca, Fe, Zn, Br, Sr, Cd, Xe, Cs, Pb, and Ra, give the electron configuration, number of valence electrons, and group number.Complete the following:- number of sublevels in n = 3; group number of carbon;- number of orbitals in 2p; sublevel being filled at atomic number 47;- maximum electrons in 3d; sublevel beginning after 4s2;- maximum electrons in one 3p orbital; valence electrons in As.Identify the element symbol for:- the first element filling 3s;- the first element with five 3p electrons;- the period 4 element in fluorine's group;- [Ar] 3d10 4s2 4p3;- the element with 3d6;- the first element completing n = 3;- the element with a half-filled 5p sublevel;- the period 6 element in magnesium's group.C. Atomic radiusPlot the supplied atomic radii for atomic numbers 1–25. Describe the period 2 trend from Li to Ne and explain why period 3 from Na to Ar follows a similar pattern.
Answers
A. Flame tests
Expected reference colors are shown below. Record what you actually observed, because burner conditions, sodium contamination, concentration, and human color perception can shift the appearance.
| Solution | Element | Typical flame color |
|---|---|---|
| CaCl2 | Ca | orange-red / brick red |
| KCl | K | lilac / pale violet |
| BaCl2 | Ba | yellow-green / apple green |
| SrCl2 | Sr | crimson red |
| CuCl2 | Cu | blue-green |
| NaCl | Na | intense yellow-orange |
Identify the unknown only by matching its observed flame with a known solution tested under the same conditions. The sheet does not provide the unknown code or color, so no unique unknown identity can be supplied.
Spaghetti-water question: sodium ions introduced by NaCl can enter the gas flame in tiny droplets. Excited sodium atoms emit intense yellow-orange light as their electrons return to lower energy states, so the flame can appear bright orange.
B. Electron configurations
The table uses noble-gas shorthand. “Valence electrons” below means electrons in the highest principal energy level, which is unambiguous for the main-group entries. Transition-metal bonding may also involve electrons.
| Atom | Ground-state electron configuration | Outer-shell valence electrons | Group |
|---|---|---|---|
| O | [He] 2s2 2p4 | 6 | 16 |
| Na | [Ne] 3s1 | 1 | 1 |
| Ca | [Ar] 4s2 | 2 | 2 |
| Fe | [Ar] 3d6 4s2 | 2 | 8 |
| Zn | [Ar] 3d10 4s2 | 2 | 12 |
| Br | [Ar] 3d10 4s2 4p5 | 7 | 17 |
| Sr | [Kr] 5s2 | 2 | 2 |
| Cd | [Kr] 4d10 5s2 | 2 | 12 |
| Xe | [Kr] 4d10 5s2 5p6 | 8 | 18 |
| Cs | [Xe] 6s1 | 1 | 1 |
| Pb | [Xe] 4f14 5d10 6s2 6p2 | 4 | 14 |
| Ra | [Rn] 7s2 | 2 | 2 |
C. Short electron-configuration questions
| Prompt | Answer |
|---|---|
| Number of sublevels in | 3: 3s, 3p, 3d |
| Carbon group number | 14 |
| Number of orbitals in 2p | 3 |
| Sublevel being filled at atomic number 47 | 4d |
| Maximum electrons in 3d | 10 |
| Sublevel that begins filling after 4s2 | 3d |
| Maximum electrons in one 3p orbital | 2 |
| Valence electrons in As | 5 |
Element identifications:
- First element that begins filling 3s: Na.
- First element with five 3p electrons: Cl.
- Period 4 element in the same group as F: Br.
- : As.
- Element with : Fe.
- First element that completes principal level : Ar.
- Element with a half-filled 5p sublevel: I ().
- Period 6 element in the same group as Mg: Ba.
D. Atomic-radius graph
Plot the supplied atomic radii against atomic number and connect adjacent points. Across period 2, the values fall overall from Li at 152 pm to F at 64 pm; the table's Ne value is 70 pm. The broad decrease occurs because nuclear charge increases while the added electrons remain in the same principal shell, so increasing effective nuclear charge pulls the valence shell inward.
Period 3 shows the same repeating pattern: a large radius at Na, then a general decline toward Ar. Each new period starts a higher principal energy level, producing a jump in radius before the across-period contraction repeats.
Conclusion
Electron configurations explain both recurring group behavior and the overall radius trend across a period. Use the reference flame colors to interpret—not replace—the colors and unknown identity observed in your own experiment.
Evidence boundary
The electron configurations and periodic-trend answers follow the printed atom list and supplied radius table. Flame colors are typical reference expectations only; the actual colors, spot-plate layout, unknown code, and unknown identity must come from the student's observations.
Sources
These references support the concepts and methods used in the explanation above.