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Atomic Structure and Forces Nucleus - center of atom Proton - (+) charge particle, in nucleus Neutron - (0) charge particle, in nucleus Electron - (-) charge, fly in cloud around nucleus Atoms by the Numbers Atomic number - The number of protons in the nucleus of the atom (defines type of element) Mass number, atomic mass - The number of protons and neutrons in the nucleus of the atom Average atomic mass - The weighted average of masses of all atoms of that element Net Charge - The difference between the number of protons and electrons in the atom Isotope - A version of an element based on differing numbers of neutrons Four Fundamental Forces of Nature Electrical Force (aka electromagnetic force) Action – Based on charges of particles. Like forces repel, opposite forces attract Effect of distance – long-range force, can act over distance, gets slightly weaker as distance increases Strength – Second strongest of the 4 fundamental forces Strong Force Action – Attracts neutrons and protons within the nucleus__________________________ Effect of distance – Short range force, strength quickly decreases with increasing distance______ Strength – 100 times stronger than the electrical force Challenge: Can you discover the other 2 fundamental forces of nature? Stability and Comparison of Forces Scenario 1: Small Nucleus (Mass Number < ~83) Strong forces overcome electrical forces. Nucleus is stable and holds together. Why does this happen? Strong forces are very strong and can win out because of the short distances involved the small nucleus. Draw figure here: Scenario 2: Large Nucleus (Mass Number > ~83) Electrical forces overcome strong forces. Nucleus is unstable and breaks apart. Why does this happen? Strong forces fall off because of increased distance so electrical repulsion breaks apart nucleus. Draw figure here: Isotopes, Ratios, and Stability Less massive elements – nucleus is stable if ratio of neutrons to protons is 1 : 1 More massive elements – nucleus is stable if ratio of neutrons to protons is _3_ : _2_ HW: Read Ch 18, Section 1. p. 536-540. Add any notes to this page that you think are relevant. Think about it: What is the ratio of neutrons to protons in an atom of lead-214? Would you expect this atom to be stable or unstable? Why? Who were the three scientists who began studying the field of radioactivity?
