1 Chemistry Chapter 3 Atomic Structure and the Nucleus World of Chemistry Zumdahl Last revision Fall 2008

2 Structure of the atom Particle Symbol Relative Electric Charge Actual Mass (g) Relative Mass Electron Proton Neutron We have all learned from an early age that the atom is composed of 3 tiny particles

3 And the atom has 2 main regions: the nucleus and the electron cloud. Nucleus Electron Cloud p+nop+no e-e- The periodic table can help us figure out the protons, neutrons and electrons for any element 19 K Potassium Atomic number: This tells the number of protons for the element Symbol: The symbol always starts with a capital letter Name Average Atomic Mass: This is the average abundance of isotopes occurring in nature = In a neutral atom e - = p + When this number is rounded to a whole number it becomes the Mass Number which is the total particles in the nucleus

4 Determining number of particles in an atom Protons = the atomic number of the element. The protons identify the atom Electrons = as long as the atom is neutral, electrons are equal to protons. Neutrons = the mass number tells the total particles in the nucleus so just subtract the atomic number from the mass number. 19 K Potassium – 19p + = 20 n o

5 Isotopes: an element with various masses. This indicates the mass number of the element

6 Symbolic notation for atoms, ions and isotopes This is also known as the complete chemical symbol or it can be written as an isotopic name: Potassium-39  Mass number + The charge implies electrons have been gained or lost and the atom is now an ion 

7 Elements occur in nature as mixtures of isotopes Carbon =98.89% 12 C 1.11% 13 C <0.01% 14 C How can you represent all the isotopes in one mass value? Atomic Masses 1. Multiply the abundance of the element by the element’s mass 2. Add the masses and divide by 100 Carbon atomic mass = amu Remember, any given sample can have this abundance of isotopes.

8 In the beginning… The big bang many particles were created and they would randomly collide and stick together. What if two protons came together? Neutrons are added as glue for the nucleus. If the balance of protons to neutrons (not always equal numbers) was not right the nucleus becomes unstable and radioactive and begins to spit off particles and/or energy to achieve a balance. These emissions are called radiation

9 Three Kinds of Nuclear Radiation Alpha decay: An alpha particle or helium nucleus is emitted from the nucleus. Beta decay: A beta particle or electron from the decay of a neutron is emitted from the nucleus. Gamma decay: A burst of gamma electromagnetic radiation is emitted from the nucleus.

10 Alpha Particles α Alpha particles contain 2p + and 2n 0 just like a helium nucleus. It’s a big particle compared to others and carries the lowest energy of the three. This kind of radiation can be blocked by paper or clothes.

11 Beta Particle β A Beta is an electron that is released from the nucleus. The electron comes from a neutron decaying. It breaks apart into a proton and an electron. The electron leaves and the proton stays behind. Beta radiation has more energy than alpha and needs at least 1 cm of aluminum or similar material to stop the radiation.

12 Gamma Radiation γ Gamma radiation is an electromagnetic wave with a very short wavelength and a very high frequency. It has very high energy. You would need 6 ft of concrete or 6 inches of lead to stop gamma rays.

13 Nuclear Reactions The nuclei can interact in two ways 1. Fusion : Two nuclei come together and fuse to make a bigger nucleus. 2. Fission : A large nucleus breaks apart and makes two or more smaller nuclei. Both interactions create large amounts of Energy!!!!