8.5A

In the early 1900s many scientists thought that an atom consisted of a positive substance with negative charges scattered throughout the substance. Then Ernest Rutherford completed an experiment that changed the concept of an atom. His discovery led to the understanding that an atom consists mostly of empty with space with-

• Protons orbiting a dense nucleus made of electrons and neutrons
• Electrons orbiting a dense nucleus made of protons and neutrons
• Neutrons and protons orbiting a cloud of electrons
• Electrons and protons orbiting a  cloud of neutrons

A model of a beryllium atom is shown below.
What types of particles are found in the cloud surrounding the atom's nucleus?

• Positively charge particles and negatively charged particles 
• Negatively charged particles only
• Neutral particles and positively charge particles
• Positively charged particles only

Which of the following best describes an electron?

• It has no charge and about the same mass as a proton.
• It has a negative charge and much less mass than a proton.
• It has a positive charge and much more mass than a neutron.
• It has a negative charge and about the same mass as a neutron.

An atom has 25 protons, 30 neutrons, and 25 electrons. What is the charge of the atom's nucleus?

• +25
• +30
• -25
• -30

Which of these best describes one of the subatomic particles that could be found at location X in the model of an atom shown above? 

• It has mass but no charge.
• It has no mass and a positive charge.
• It has a large mass and a negative charge.
• It has no mass and an equal number of positive and negative charges.