Electronic configuration and the Periodic Table
Introduced| English | Meaning |
|---|---|
| electronic configuration/ɪlekˈtrɒnɪk kənˌfɪɡjəˈreɪʃn/ | The arrangement of electrons among an atom's or ion's shells, subshells and orbitals. |
| group/ɡruːp/ | A vertical column in the periodic table whose elements have related outer-electron configurations and chemical properties. |
| period/ˈpɪərɪəd/ | A horizontal row of the periodic table, corresponding to the principal shell occupied by the outer electrons of its elements. |
How electrons are arranged
- Electrons aren't scattered randomly — they fill up shells around the nucleus in a set order.
- This arrangement explains the whole shape of the Periodic Table.
What is the maximum number of electrons in the first (innermost) shell?
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The first shell holds up to 2 electrons.
Filling the shells
- Electrons fill the innermost shell first, then the next.
- The shells hold up to 2, then 8, then 8 electrons (at this level).
An atom has a tiny nucleus of protons and neutrons, with electrons in shells around it
The electronic configuration of sodium (11 electrons) is:
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Fill inner shells first: 2, 8, then 1.
Chlorine has 17 electrons, giving the configuration 2, 8, ______.
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2 + 8 + 7 = 17 electrons.
Writing the configuration
- The electronic configuration 电子排布 lists how many electrons are in each shell.
- Example: sodium (11 electrons) is 2, 8, 1.
Worked example. Chlorine has 17 electrons. Fill the shells: 2, then 8, then the remaining 7 → configuration 2, 8, 7. The 7 outer electrons place it in Group 族 VII.
Fill the electron shells
Electrons fill the inner shell first (max 2), then the next (max 8). The number in the OUTER shell is the group number — chlorine's 2,8,7 puts it in Group VII.
An element with 7 electrons in its outer shell is in:
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Outer electrons = group number, so 7 → Group VII.
The number of electron shells an atom uses equals its period number.
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Period = number of occupied shells.
Link to the Periodic Table
- The number of outer-shell electrons = the group number.
- The number of shells used = the period 周期 number.
The outer shell decides the chemistry. Elements in the same group have the same number of outer electrons, so they react in similar ways. That's why the group number is so important.
You've got it
- electrons fill shells from the inside out: 2, 8, 8
- the electronic configuration lists electrons per shell (e.g. sodium 2,8,1)
- outer electrons = group number; number of shells = period number