Negatively charged sub-atomic particles.

The negatively charged sub-atomic particles are called electrons. They are located in the space surrounding the nucleus of an atom. Here are the steps to understand this:

1. Understand the structure of an atom: An atom is made up of three types of sub-atomic particles - protons, neutrons, and electrons. Protons carry a positive charge, neutrons carry no charge, and electrons carry a negative charge.

2. Identify the location of these particles: In an atom, protons and neutrons are located in the nucleus (center of the atom), while electrons orbit around the nucleus in a cloud-like formation.

3. Understand the charge of an electron: Electrons are negatively charged. This means they have the ability to attract positively charged particles.

4. Understand the role of electrons: Electrons play a crucial role in the creation of chemical bonds. They are also responsible for an atom's reactivity and the physical properties of the elements.

5. Remember the key point: The negatively charged sub-atomic particles in an atom are called electrons.