Electron

Two numbers define it on the AP Physics 2 and AP Physics C: Electricity and Magnetism Tables of Information: $m_e = 9.11 \times 10^{-31}$ kg and, through the elementary charge, $e = 1.60 \times 10^{-19}$ C. The AP Physics 1 and C: Mechanics tables print neither, because neither course needs them.

The sign is a definition you should be able to quote. Essential knowledge 10.1.A.1.ii calls the magnitude of the charge of a single electron or proton the elementary charge $e$, the smallest indivisible amount of charge, and 10.1.A.1.iii assigns the signs: the charge of an electron is $-e$, the charge of a proton is $+e$, and a neutron has none.

In a circuit, the electron is the thing that actually moves. Statement 11.1.A.2.ii says in common circuits, current is actually due to the movement of electrons, negative charge carriers, while 11.1.A.2.i defines the direction of conventional current as the direction positive charge would move. Those two point opposite ways, and the AP Physics 2 exam conventions box settles it in four words: "Current is conventional current." So draw and calculate with conventional current, and keep the electron picture for explaining why a conductor conducts.

Mass is where the electron matters least. Dividing the sheet values gives a proton about 1800 times heavier, which is why 15.2.A.2.iii puts essentially all of an atom's mass in its nucleus. What the electrons set instead is behaviour: 15.2.A.2.i says their number and arrangement affects how atoms interact.