Bond polarity and electronegativity
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All 11 Flashcards — Bond polarity and electronegativity
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Question
What is electronegativity?
Answer
A measure of how strongly an atom **attracts the shared (bonding) electrons** in a covalent bond.
Question
What makes a bond polar?
Answer
A **difference in electronegativity** between the two atoms — the electrons are pulled towards the more electronegative atom.
Question
Which atom becomes δ−?
Answer
The **more electronegative** atom (it gets a bigger share of the electrons); the less electronegative atom is **δ+**.
Question
Pure covalent vs polar covalent vs ionic?
Answer
Δχ = 0 → **pure covalent**; small Δχ → **polar covalent** (δ+/δ−); large Δχ → **ionic**.
Question
What is a bond dipole?
Answer
The small separation of charge (δ+ → δ−) along a polar bond; drawn as an **arrow** pointing to the δ− atom.
Question
When is a molecule with polar bonds non-polar?
Answer
When the molecule is **symmetrical**, so the bond dipoles **cancel** (e.g. CO_{2}, CCl_{4}, BF_{3}).
Question
Why is CO_{2} non-polar?
Answer
It is **linear** — the two equal C=O dipoles point in opposite directions and **cancel**.
Question
Why is H_{2}O polar?
Answer
It is **bent** (lone pairs on O), so the two O–H dipoles **do not cancel** and give a net dipole.
Question
Does NH_{3} have a net dipole?
Answer
Yes — it is **trigonal pyramidal** (a lone pair on N), so the N–H dipoles do not cancel; NH_{3} is polar.
Question
What two things must a 'why is X polar?' answer mention?
Answer
(1) the bonds are **polar** (electronegativity difference) and (2) the **shape** means the dipoles **do not cancel**.
Question
Is Cl_{2} polar?
Answer
No — both atoms are identical, so Δχ = 0; the bond is **non-polar** and there is no dipole.
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Topic 2.2 hub
The covalent model
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