The Atomic Nucleus

Atoms Reminder: Matter is made up of small particles called atoms

Atomic Structure Reminder: 2 areas in the atom nucleus: middle of the atom; most of the atom’s mass electron cloud: surrounds the nucleus; mostly empty space

Structure of the Nucleus Reminder: 2 subatomic particles:

Discovery of the Nucleus Rutherford 1911 Demonstrates the existence of a positively charged nucleus that contains nearly all the mass of an atom

The Nucleus

Inside Protons and Neutrons Protons and Neutrons are made up of smaller particles called Quarks Each proton and neutron is made up of 3 quarks

What Holds the Nucleus Together Opposite charges attract and like charges repel Protons should repel one another What’s Holding Them Together?

The Strong Nuclear Force The Strong Nuclear Force is one of 4 fundamental forces in the universe The others are gravity, the weak nuclear force, and electromagnetism (what causes like charges to repel)

Electromagnetic Force FORCES IN THE ATOM Gravitational Force Electromagnetic Force Strong Force Weak Force

Gravitational Force The force of attraction of objects due to their masses The amount of gravity between objects depends on their masses and the distance between them Do you think this force plays a significant role in holding the atom together?

Electromagnetic Force The force that results from the repulsion of like charges and the attraction of opposites The force that holds the electrons around the nucleus + + + - - - Notice how the particles with the same charge move apart and the particles with different charges move together. Why are neutrons not pictured above?

Notice how the original particle changes to something new. Weak Force This force plays a key role in the possible change of sub-atomic particles. For example, a neutron can change into a proton(+) and an electron(-) The force responsible for radioactive decay. Radioactive decay  process in which the nucleus of a radioactive (unstable) atom releases nuclear radiation. Notice how the original particle changes to something new. + n -

Would an atom have a nucleus if the strong force did not exist? The force that holds the atomic nucleus together The force that counteracts the electromagnetic force Notice how the electromagnetic force causes the protons to repel each other but, the strong force holds them together. + + + + Would an atom have a nucleus if the strong force did not exist?

The Strong Nuclear Force Strongest of the Forces Must work at close range

When The Strong Force Isn’t Strong Enough Reminder: Isotopes: Atoms of the same element with different numbers of neutrons and masses Most isotopes are stable, but some are unstable Unstable: The nucleus has too many neutrons to hold itself together (ie the strong nuclear force is not strong enough) Strong Force isn’t strong enough = RADIOACTIVITY ex. Uranium is radioactive because the nucleus is so BIG!

Radioactivity Radioactive: An unstable nucleus releases energy and radiation particles (nuclear radiation) to become more stable Types of Radiation Particles: Alpha particles Beta particles Gamma Rays (Helium Nucleus) (negative particle from neutron) (Gamma photon)

Radioactivity Types of Radiation Particles: Alpha particles α Can be stopped by paper Beta particles β Can be stopped by wood Gamma Rays γ Can be stopped by lead or concrete

Radioactivity

Uses of Radioactivity Radiometric dating Smoke Detectors Pest control Treating Cancer Other medical uses Nuclear energy uses energy from the nucleus

Energy from the Nucleus Nuclear Fission: When a large nucleus splits into two smaller nuclei and releases energy Used in nuclear energy plants and atomic bombs See Animations

Energy from the Nucleus Nuclear Fusion: When two or more small nuclei combine, or fuse, to form a larger nucleus Happens in the Sun Hydrogen (small)  Helium (bigger) = LOTS OF ENERGY (Light and Heat)