Practice ECAT Chemistry questions with answers and explanations.
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Oxygen has two bonding pairs and two lone pairs.
Lone-pair repulsion produces a bent molecule.
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After formation, a coordinate bond behaves like an ordinary covalent bond.
The electron-pair donor provides both bonding electrons.
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Thomson's cathode-ray experiments revealed negatively charged particles.
He proposed an early model with electrons in positive matter.
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Periodic trends arise from repeating valence-shell patterns.
The periodic table organizes these regularities.
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Chadwick identified the neutral nuclear particle in 1932.
Neutrons explain isotopic mass differences.
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Alkali metals have one valence electron.
They commonly form +1 ions and are highly reactive.
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Quantum mechanics describes electron probability distributions.
An orbital can hold up to two electrons with opposite spins.
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Halogens have seven valence electrons.
They commonly form -1 ions.
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The Pauli exclusion principle allows two electrons per orbital.
They must have opposite spin quantum numbers.
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Noble gases have filled valence shells in their common ground states.
They are generally unreactive.
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An s subshell contains one orbital.
It can hold a maximum of two electrons.
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Increasing nuclear charge pulls electrons closer within the same main shell.
Effective nuclear attraction generally increases across a period.
