CHEM 251 1st Edition Lecture 1 Outline of Last Lecture I. N/AOutline of Current Lecture II. Origin of the Periodic TableIII. Different Depictions of the Periodic TableIV. Periodic TrendsCurrent LectureII. Origin of the Periodic Tablea. The common modern form:b. Development of the periodic tablei. 1863: John Newlands-“Law of Octaves”ii. Mendeleev-8 groups, weird bunches of metals, laid groundwork for modern periodic tablec. Breaking down the Periodic Tablei. Atomic number: number of protons (also the number of electrons)ii. One element may have many isotopes-containing different numbers of neutronsiii. Atomic weight-average of all naturally abundant isotopesiv. As the number of protons increases, the ratio of neutrons to protons increases1. Why? More neutrons are needed to distribute the repulsive interactions between protons These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.III. Different Depictions of the Periodic Tablea. Periodic table does not have to be organized a certain whyb. Some alternative views:IV. Periodic Trendsa. Parsing the periodic tablei. Across = period1. Elements in the same period have different properties but related orbital structureii. Down = group1. Elements in the same group have similar propertiesiii. Group 1 = alkali metalsGroup 2 = alkaline earth metalsGroups 3-12 = transition metalsGroup 13Group 14Group 15 = pnictogensGroup 16 = chalcogensGroup 17 = halidesGroup 18 = nobel gasesb. Physical Propertiesi. Metals: often exhibit ductility (stretchable) or malleability (squishable), highly conductive in three dimensionsii. Weak metals: A little bit less metalliciii. Semi-metals: Even less metallic — these tend to form small molecules rather than metallic sheetsiv. Non-metals: These are clearly not metals — non-conducting, often liquidsor
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