Presentation on theme: "History & Classification"— Presentation transcript:
1 History & Classification Periodic TableHistory & Classification
2 Mendeleev’s Periodic Table-1869 Arranged elements based on their atomic massDmitri MendeleevOrganized by increasing atomic massElements with similar properties are grouped togetherPredicted properties of undiscovered elements2
5 Henry Mosely (1913, British) Organized elements according to atomic numberResolved discrepancies in Mendeleev’s arrangements
6 The Periodic Table Period Group or Family Group or family Period Roman Numeral = Valence electronsGroup or familyPeriod
7 Periods and Groups Horizontal Rows Groups or Families Group Numbers Numbered 1-7Groups or Familiesgroups contain elements with similar properties in vertical columns.Group Numbersuse the letter A for the representative elements (1A to 8A) and the letter B for the transition elements.also use numbers 1-18 to the columns from left to right
9 Names of Some Representative Elements Several groups of representative elements are known by common names.
10 The Properties of a Group: the Alkali Metals Easily lose valence electron(Reducing agents) React violently with water Large hydration energy React with halogens to formsalts
11 Properties of Metals Metals are malleable Metals are ductile Metals are good conductors of heat and electricityMetals are malleableMetals are ductileMetals have high tensile strengthMetals have luster
12 Examples of MetalsPotassium, K reacts with water and must be stored in keroseneCopper, Cu, is a relatively soft metal, and a very good electrical conductor.Zinc, Zn, is more stable than potassiumMercury, Hg, is the only metal that exists as a liquid at room temperature
13 Properties of Nonmetals Carbon, the graphite in “pencil lead” is a great example of a nonmetallic element.Nonmetals are poor conductors of heat andelectricityNonmetals tend to be brittleMany nonmetals are gases at room temperature
14 HalogensGroup 7A(17) the halogens, includes chlorine, bromine, and iodine.
15 Examples of NonmetalsMicrospheres of phosphorus, P, a reactive nonmetalSulfur, S, was once known as “brimstone”Graphite is not the only pure form of carbon, C. Diamond is also carbon; the color comes from impurities caught within the crystal structure
16 Properties of Metalloids Metalloids straddle the border between metals and nonmetals on the periodic table.They have properties of both metals and nonmetals.Metalloids are more brittle than metals, less brittle than most nonmetallic solidsMetalloids are semiconductors of electricitySome metalloids possess metallic luster
17 Silicon, Si – A Metalloid Silicon has metallic lusterSilicon is brittle like a nonmetalSilicon is a semiconductor of electricityOther metalloids include:Boron, BGermanium, GeArsenic, AsAntimony, SbTellurium, Te