🗂️ Structure: Groups and Periods
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The periodic table is divided into groups (columns, from top to bottom) and periods (rows, from left to right).
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- Groups: Elements in a group share similar chemical properties because they have the same number of outer electrons (valence electrons). There are 18 main groups, e.g., the alkali metals (group 1) or noble gases (group 18).
- Periods: Elements in a period have the same number of electron shells. From left to right, the atomic number increases, as does the nucleus size.
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Term Meaning Example Group same valence electrons, similar reactions Group 17: Halogens (e.g. chlorine) Period same number of electron shells 3rd period: sodium to argon -
This creates horizontal and vertical relationships in the PTE, helping predict many properties of the elements.
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