Chapter 32 The Atom and the Quantum Herriman High Physics

The Atom Protons – Found in the Nucleus Carry a Positive Charge Have a Mass of 1 x kg Neutrons – Found in the Nucleus Carry no charge Have a mass that is approximately the same as a Proton Electrons – travel around the nucleus in specific orbits related to their energy Carry a negative charge Have a mass of 9 x kg Herriman High Physics

Light Quanta Light has a dual nature – it is made up of packets of energy called quanta or photons which are carried on a wave. When an atom absorbs energy electrons move from their normal or ground state to a higher energy or excited state. To go back to their ground state atoms give off this excess energy as light. Herriman High Physics

The Energy of a Photon The energy of any photon of light given off in this way is determined by the equation: E = hf Where E = energy in joules h = x Js (Planck’s Constant) f = frequency of the light Herriman High Physics

The Photoelectric Effect The photoelectric effect is the ejection of electrons from a material when light falls upon it. The material is sensitive to the frequency of the light not its intensity. Herriman High Physics

Light as a Particle Light as a Wave Light has a dual nature, it acts like a particle and as a wave. The fact that light can be bent by gravity shows that light acts like a particle. The fact that light undergoes reflection, refraction, and diffraction shows that it behaves like a wave. Reflection – turning back at a boundary Refraction –the bending of light as it moves from one substance to another. Diffraction – the bending of light around an object Herriman High Physics

Chapter 33 The Atomic Nucleus and Radioactivity Herriman High Physics

Nuclear Energy The Nucleus of an atom contains Protons – Positively Charged Neutrons – no charge Atomic Mass Number – denoted by the letter A, this number represents the total number of protons + neutrons in the nucleus, telling you what isotope of the element you have. Atomic Number – denoted by the letter Z, this number represents the number of protons in the nucleus, telling you what element you have. Herriman High Physics

Nuclear Energy Atomic Symbol for a given isotope of an element is generally given as noted to the right. A prime example is an alpha particle or helium nucleus Herriman High Physics

Nuclear Reactions Two Types of Nuclear reactions produce vast amounts of energy according to Einstein’s famous equation E = mc 2 Fission – the splitting of an atom into smaller parts Fusion- the joining of two small nuclei to produce one larger nucleus Herriman High Physics

Nuclear Reactions Mass defect – is the amount of mass that is converted to energy during fission or fusion. Calculation of Mass defect is the difference between the actual mass of the atom and the known mass of each of its parts Herriman High Physics

Radioactivity Three types of Radioactivity Alpha – α – is the nucleus of a helium atom Can be stopped by a sheet of paper, is harmful only if ingested Beta – β – emission of an electron or positron Can be stopped by a sheet of lead, is harmful to all living tissue Gamma – γ – emission of a high energy photon Cannot be completely stopped. Very harmful to all living tissue. Herriman High Physics

Nuclear Reactions Alpha Decay Beta Decay Gamma Emission Herriman High Physics

Radioactive Half Life By definition, the amount of radioactive material that decays to another material is determined by its half life. A half life is the amount of time required for ½ of the sample to decay. The equation for a half life is: Where a 0 is the amount you start with and a is the amount you have left after x half lives. Herriman High Physics

Sample Problem If a 20 gram sample of with a half live of 10 hours is allowed to decay for 3 days, how much will remain at the end of that time? Herriman High Physics

Solution Herriman High Physics

Transmutation of Elements When a nucleus emits an alpha or a beta particle it becomes a new element – this process is called transmutation. This can occur naturally or artifically. This process can be useful for dating objects, or a a tracer in medical procedures. Herriman High Physics

Chapter 34 Nuclear Fission and Fusion Herriman High Physics

Applications of Nuclear Processes Energy can be released in a nuclear reaction by one of two processes: Fission – the splitting of a nucleus into smaller nuclei Fusion – the joining of two smaller nucleui into a larger nuclei Herriman High Physics

Fission Fission is the breaking of a large nucleus into smaller nuclei. Usually caused by neutron bombardment of the nucleus, causing the nucleus to split Mass is converted into energy All current nuclear reactor technology uses fission Fission is controlled by using a moderator, a material which absorbs neutrons to keep the chain reaction under control Herriman High Physics

Fusion Fusion reactions take lighter nuclei, often an isotope of hydrogen called deuterium and fuse them together to make a heavier nuclei, often helium This must occur at high energy and is very difficult to produce under laboratory conditions Currently no workable fusion reactor has been produced on earth The sun and stars all produce energy due to nuclear fusion Herriman High Physics