Electronic structure of the first twenty elements
| English | Français |
|---|---|
| electron shell/ɪˈlektrɒn ʃel/ | electron shell |
| electronic structure/ɪlekˈtrɒnɪk ˈstrʌktʃə/ | electronic structure |
What would explain this observation?
- Sodium has eleven electrons in its neutral atom. Its arrangement 2,8,1 is a distribution across shells, not the three digits of its atomic number.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- Electrons occupy the lowest available energy levels, also called shells. For the first twenty elements the GCSE model places two in the first shell, then up to eight in the second, then eight in the third before the fourth begins. Sodium is 2,8,1 and calcium is 2,8,8,2. Draw a central nucleus and concentric shells with the correct electron counts. The drawing represents energy levels; shell radii and electron sizes are not to scale.
- electron shell 电子层: An energy level occupied by electrons outside the nucleus in the atomic model; electronic structure 电子排布: The distribution of electrons among an atom’s energy levels.
Which is the electronic structure of a neutral calcium atom, Z=20?
The first twenty arrangements are H 1; He 2; Li 2,1; Be 2,2; B 2,3; C 2,4; N 2,5; O 2,6; F 2,7; Ne 2,8; Na 2,8,1; Mg 2,8,2; Al 2,8,3; Si 2,8,4; P 2,8,5; S 2,8,6; Cl 2,8,7; Ar 2,8,8; K 2,8,8,1; Ca 2,8,8,2. Verify every sum against the neutral atom’s proton number. This simplified sequence should not be extrapolated to every later element or used to claim the third shell can never contain more than eight.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- The first twenty arrangements are H 1; He 2; Li 2,1; Be 2,2; B 2,3; C 2,4; N 2,5; O 2,6; F 2,7; Ne 2,8; Na 2,8,1; Mg 2,8,2; Al 2,8,3; Si 2,8,4; P 2,8,5; S 2,8,6; Cl 2,8,7; Ar 2,8,8; K 2,8,8,1; Ca 2,8,8,2. Verify every sum against the neutral atom’s proton number. This simplified sequence should not be extrapolated to every later element or used to claim the third shell can never contain more than eight.
- Start with the atomic number from the supplied periodic table. For a neutral atom count that many electrons, fill the inner levels first and write a comma-separated arrangement. Convert it to a diagram by placing the exact number of dots on each ring and label the element. For an ion, adjust electron number before drawing and retain the unchanged nucleus; ion notation and brackets belong with the diagram.
Which two habits make the investigation or model in this case more defensible?
Start with the atomic number from the supplied periodic table. For a neutral atom count that many electrons, fill the inner levels first and write a comma-separated arrangement. Convert it to a diagram by placing the exact number of dots on each ring and label the element. For an ion, adjust electron number before drawing and retain the unchanged nucleus; ion notation and brackets belong with the diagram.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- Known: sulfur has Z=16, so a neutral atom has sixteen electrons. Put two in shell one, eight in shell two and the remaining six in shell three: 2,8,6. An S²⁻ ion has two additional electrons and arrangement 2,8,8. Both retain sixteen protons, while the ion has eighteen electrons and net charge −2.
A neutral chlorine atom has structure 2,8,7. How many electrons are present altogether? Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
A neutral chlorine atom has structure 2,8,7. How many electrons are present altogether?
The result is 17 electrons. Known: sulfur has Z=16, so a neutral atom has sixteen electrons. Put two in shell one, eight in shell two and the remaining six in shell three: 2,8,6. An S²⁻ ion has two additional electrons and arrangement 2,8,8. Both retain sixteen protons, while the ion has eighteen electrons and net charge −2.
Check the conclusion and its limits
- The second number in 2,8,6 is a count, not an electron charge or radius. Filling an outer shell while leaving an available inner level empty is incorrect for these ground-state atoms. Helium is stable with two electrons in its only shell; a full outer shell does not always mean eight.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
Every stable full outer shell must contain eight electrons. This claim is false: The second number in 2,8,6 is a count, not an electron charge or radius. Filling an outer shell while leaving an available inner level empty is incorrect for these ground-state atoms. Helium is stable with two electrons in its only shell; a full outer shell does not always mean eight.
Electronic structure of the first twenty elements: The first twenty arrangements are H 1; He 2; Li 2,1; Be 2,2; B 2,3; C 2,4; N 2,5; O 2,6; F 2,7; Ne 2,8; Na 2,8,1; Mg 2,8,2; Al 2,8,3; Si 2,8,4; P 2,8,5; S 2,8,6; Cl 2,8,7; Ar 2,8,8; K 2,8,8,1; Ca 2,8,8,2. Verify every sum against the neutral atom’s proton number. This simplified sequence should not be extrapolated to every later element or used to claim the third shell can never contain more than eight.
Every stable full outer shell must contain eight electrons.
The second number in 2,8,6 is a count, not an electron charge or radius. Filling an outer shell while leaving an available inner level empty is incorrect for these ground-state atoms. Helium is stable with two electrons in its only shell; a full outer shell does not always mean eight.
An energy level occupied by electrons outside the nucleus in the atomic model: write the technical term.
electron shell means An energy level occupied by electrons outside the nucleus in the atomic model.