According to the modern day model of the atom, the nucleus of an atom is surrounded by one or more

Answer is: electrons.

According to the Bohr model of the atom:

1. Electrons orbit the nucleus in orbits that have a set size and energy.

2. Energy levels of electrons are discrete (certain discrete values of energy).

3. Electrons can jump from one energy level to another, absorbing or emitting electromagnetic radiation with a frequency ν (energy difference of the levels).

The electron (symbol: e⁻) is a subatomic particle whose electric charge is negative one elementary charge.

Proton is a subatomic particle with a positive electric charge of +1e elementary charge.

Beside negatively charged electrons, atoms have positively charged protons, so atoms have neutral charge.