Practice NAT Chemistry questions with answers and explanations.
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Carbon in methane has four bonding pairs and no lone pairs.
The molecular geometry is tetrahedral.
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Nitrogen has three bonds and one lone pair.
The lone pair changes the molecular shape from tetrahedral electron geometry.
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Oxygen has two bonding pairs and two lone pairs.
Lone-pair repulsion produces a bent molecule.
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Carbon has two electron domains from the two double bonds.
They arrange 180 degrees apart.
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Boron has three bonding regions and no lone pairs.
The molecule is planar with approximately 120-degree angles.
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The octet rule is a useful main-group bonding guideline.
Hydrogen, boron, and expanded-valence species are exceptions.
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Lewis structures use lines and dots for bonds and lone pairs.
They help predict connectivity and formal charge.
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Noble gases have filled valence shells in their common ground states.
They are generally unreactive.
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Increasing nuclear charge pulls electrons closer within the same main shell.
Effective nuclear attraction generally increases across a period.
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Additional electron shells are added down a group.
This outweighs the increased nuclear charge.
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Effective nuclear charge generally increases across a period.
Electrons are therefore harder to remove, with some exceptions.
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Valence electrons are farther from the nucleus and more shielded down a group.
They are generally easier to remove.
