Electric charge

Charge is a fundamental property of all matter, and AP Physics 2 pins it down with four statements. There are two signs and no third, so neutral means the two cancel rather than that charge is absent. The elementary charge $e$ is the smallest indivisible amount, printed on the sheet as $e = 1.60 \times 10^{-19}$ C. An electron carries $-e$, a proton $+e$, a neutron none. A point charge is a model you justify, not a property an object owns.

Put the first two together and charge is quantized: every net charge you meet is a whole-number multiple of $e$. A reading of $-4.8$ nC is exactly $3.0 \times 10^{10}$ surplus electrons, and no AP question will hand you a fraction of one.

Charge is also conserved. A system's net charge stays constant unless charge is transferred to or from it, and in ordinary matter what moves is electrons. Friction, contact and grounding all shuffle electrons between objects; none of them creates charge.

The unit is the coulomb, and one coulomb is a huge amount of it: two 1 C charges a meter apart would repel with $9.0 \times 10^9$ N. That is why exam charges arrive in microcoulombs and nanocoulombs. The Coulomb's law guide works the force between charges step by step.