Practice Flashcards
What does the bonding triangle (van Arkel–Ketelaar) show?
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All Flashcards in Topic 2.4
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2.4.111 cards
What does the bonding triangle (van Arkel–Ketelaar) show?
That ionic, covalent and metallic bonding are the three **extremes** of one **continuum** — real compounds sit in between.
What are the three corners of the bonding triangle?
**Metallic** (bottom-left), **covalent** (bottom-right) and **ionic** (top).
What is electronegativity (χ)?
How strongly an atom **attracts a shared pair of electrons**; values are in the data booklet.
How do you find χ_avg?
Average the two electronegativities: $\chi_{avg} = \dfrac{\chi_A + \chi_B}{2}$ — it sets the **horizontal** position.
How do you find Δχ?
Take the difference: $\Delta\chi = |\chi_A - \chi_B|$ — it sets the **vertical** (ionic) position.
What does a large Δχ tell you?
Electrons are essentially **transferred** → the bonding is **ionic** (high up the triangle).
What does a small Δχ with high χ_avg tell you?
Electrons are **shared** between similar non-metals → **covalent** (bottom-right corner).
What does a small Δχ with low χ_avg tell you?
A sea of delocalised electrons among metal atoms → **metallic** (bottom-left corner).
Place NaCl, Cl_{2} and Na on the triangle.
NaCl → **ionic** (top, large Δχ); Cl_{2} → **covalent** (bottom-right); Na → **metallic** (bottom-left).
Why is the triangle better than 'metal + non-metal = ionic'?
It uses the **actual χ values**, so it correctly classifies polar-covalent metal compounds like BeCl_{2}.
How is ionic bonding distinguished from covalent in terms of electrons?
Ionic = electrons **transferred** (large Δχ); covalent = electrons **shared** (small Δχ).
2.4.212 cards
What is an alloy?
A **mixture** of a metal with one or more other elements (it is **not** a compound — no fixed ratio).
Why is an alloy harder than a pure metal?
Its **different-sized atoms disrupt the regular layers**, so the layers **cannot slide** over each other as easily.
Do alloys still conduct electricity?
Yes — they keep **metallic bonding** (a sea of delocalised electrons); they are just **harder** than the pure metal.
Name two everyday alloys and their metals.
**Brass** = copper + zinc; **steel** = iron + carbon (also bronze = copper + tin).
What is a monomer?
A **small molecule** that joins to many others to form a **polymer** (a giant molecule).
What is an addition polymer?
A long-chain molecule made by joining many **alkene monomers** (with **C=C**), with **no atoms lost**.
What happens to the C=C during addition polymerisation?
The **double bond opens up** — one bond becomes a single bond, the other joins to the next monomer.
What is a repeating unit?
The part of the polymer chain that **repeats**; get it by **opening the C=C** and drawing a bond out of each end.
Monomer vs repeat unit?
**Monomer** has the **C=C double bond**; **repeat unit** has a **single** C–C bond with a bond out of each end.
How do you find the monomer from a polymer?
Take **one repeating unit** and **put the C=C double bond back** between the two carbons.
Monomer of poly(ethene)?
**Ethene, CH_{2}=CH_{2}** — the repeat unit is –CH_{2}–CH_{2}–.
Why is poly(ethene) a useful material?
It is **chemically unreactive (inert)** and waterproof, so it resists corrosion — useful for packaging and containers.
Topic 2.4 study notes
Full notes & explanations for From models to materials
Chemistry exam skills
Paper structures, command terms & tips
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