ECAT MCQs

Electron groups arrange to minimize repulsion.
Lone pairs and bonding regions determine molecular geometry.

Two electron groups arrange 180 degrees apart.
This minimizes repulsion.

Three electron groups arrange about 120 degrees apart.
They lie in one plane.

Four electron groups point toward tetrahedral corners.
The ideal bond angle is about 109.5 degrees.

Carbon in methane has four bonding pairs and no lone pairs.
The molecular geometry is tetrahedral.

Nitrogen has three bonds and one lone pair.
The lone pair changes the molecular shape from tetrahedral electron geometry.

Electron affinity reflects attraction for an added electron.
Its sign and magnitude vary across the periodic table.

Bond polarity arises from electronegativity differences.
The more electronegative atom gains partial negative charge.

Electronegativity helps predict bond polarity.
Fluorine has the highest common electronegativity.

Identical atoms form nonpolar covalent bonds.
Small electronegativity differences also give nearly nonpolar bonds.

Valence electrons largely determine chemical reactivity.
Elements in a group often share similar valence configurations.

Thomson's cathode-ray experiments revealed negatively charged particles.
He proposed an early model with electrons in positive matter.