Chemical trends of groups and period 3
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Question
What do elements in the same group share?
Answer
The same number of **outer (valence) electrons**, so they react in similar ways.
Question
How does group 1 reactivity change down the group?
Answer
It **increases** — the outer electron is further out and more shielded, so it is **lost more easily**.
Question
How does group 17 reactivity change down the group?
Answer
It **decreases** — the atom is bigger, so an incoming electron is **harder to gain**.
Question
Why is potassium more reactive than lithium?
Answer
K is lower in group 1: **bigger atom + more shielding** → outer electron lost more easily.
Question
Why is fluorine more reactive than iodine?
Answer
F is smaller with less shielding, so it **gains** an electron more easily.
Question
What does amphoteric mean?
Answer
Able to act as **both an acid and a base** — reacts with acids **and** alkalis (e.g. Al_{2}O_{3}).
Question
How does metallic character change across period 3?
Answer
It **decreases** — elements change from **metallic** (Na) to **non-metallic** (Cl, Ar).
Question
Acid–base trend of period-3 oxides?
Answer
**Basic → amphoteric → acidic** left to right (Na_{2}O/MgO basic, Al_{2}O_{3} amphoteric, SO_{3} acidic).
Question
Are metal oxides acidic or basic?
Answer
**Basic** (e.g. Na_{2}O, MgO). Non-metal oxides are **acidic** (e.g. SO_{3}, P_{4}O_{10}).
Question
Most reactive group-1 + group-17 pair?
Answer
**Caesium + fluorine** — lowest (most reactive) metal + top (most reactive) halogen.
Question
Reactivity order in group 1?
Answer
Li < Na < K < Rb < Cs (increases down).
Question
Reactivity order in group 17?
Answer
F > Cl > Br > I (decreases down).
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Topic 3.1 hub
The periodic table: classification of elements
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