Atomic Structure and Electron Configuration
Introduced| English | Meaning |
|---|---|
| electrons/ɪˈlektrɒnz/ | Negatively charged subatomic particles found outside atomic nuclei. |
| Coulombic attraction/kuːˈlɒmbɪk əˈtrækʃn/ | Coulombic attraction |
| electron configuration/ɪˈlektrɒn kənˌfɪɡjəˈreɪʃn/ | The distribution of an atom's or ion's electrons among its shells, subshells and orbitals. |
Inside the tiniest brick
- Everything is built from unimaginably small building blocks.
- Each has a dense core, circled by a cloud of lighter partners.
- Where those partners sit decides how the block behaves.
- A tidy address system tells us exactly where each one lives.
Nucleus and shells
- An atom has a tiny nucleus of protons and neutrons.
- Electrons 电子 occupy shells around it.
- Opposite charges attract, so the nucleus grips them by Coulombic attraction 库仑吸引.
An atom: a tiny nucleus of protons and neutrons, with electrons in shells
What holds the electrons to the nucleus?
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Opposite charges attract; the positive nucleus pulls the negative electrons.
Shells, subshells, orbitals
- Electrons fill energy levels called shells (1, 2, 3, ...).
- Each shell holds subshells labelled s, p, d, f.
- Lower shells fill first — they sit closer and are held more tightly.
The subshells within a shell are labelled s, p, d, and ____.
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The subshell labels are s, p, d, f.
Writing the configuration
- The electron configuration 电子排布 lists where the electrons sit.
- Fill in order: $1s^2\ 2s^2\ 2p^6\ 3s^2\ \dots$ (the Aufbau order).
- Oxygen, with 8 electrons, is $1s^2\ 2s^2\ 2p^4$.
Fill the electron shells
Add electrons shell by shell for sodium and read off its electron configuration.
What is the electron configuration of oxygen (8 electrons)?
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2 + 2 + 4 = 8 electrons, filling 1s, 2s, then 2p.
The configuration $1s^2\ 2s^2\ 2p^6\ 3s^1$ describes an atom with how many electrons?
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$2 + 2 + 6 + 1 = 11$ electrons -- sodium.
Write the electron configuration of sodium (11 electrons).
- Fill in order: $1s^2\ 2s^2\ 2p^6\ 3s^1$.
- The single $3s^1$ is its lone outer (valence) electron.
Which subshell fills first?
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By energy order, $4s$ is lower and fills before $3d$.
Inner-shell electrons are easier to remove than outer-shell electrons.
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False. Inner electrons are closer to the nucleus and feel a stronger Coulombic pull, so they are much harder to remove.
Electrons fill the lowest-energy subshell first, but the order is not strictly by shell number — $4s$ fills before $3d$. The superscripts must add up to the total electron count, so always check the sum. And the closer a shell is to the nucleus, the stronger the Coulombic pull, so inner electrons are far harder to remove than outer ones.
An atom is a nucleus of protons and neutrons with electrons in shells, held by Coulombic attraction. Electrons fill subshells (s, p, d, f) lowest-energy first, and the electron configuration records the result, like sodium's $1s^2\,2s^2\,2p^6\,3s^1$. Inner shells, held tightest, fill before outer ones.