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History of the Periodic Table Dimitri Mendeleev published a periodic table that arranged elements by increasing atomic mass This did not accurately group elements by similar properties The modern table is arranged by increasing atomic number Periodic Law – there is a periodic repetition of physical and chemical properties when elements are arranged by increasing atomic Some of Medeleev’s work (1869) number Periodic Table (a review) Groups go down the table Elements in the same group have similar properties Periods go across the table Chemical properties of the elements change in a predictable manner going across a period Periodic Table review (cont) Group 1A – alkali metals Group 2A – alkaline earth metals Group 6A - chalcogens Group 7A – halogens Group 8A – noble gases Metals are to the left of the staircase Non-metals are to the right of the staircase Metalloids are along the staircase (B, Si, Ge, As, Sb, Te, Po) Periodic Trends Atomic radius Ionization energy Electronegativity Atomic Radius The size (radius) of an atom of that element Increases moving down a group Decreases moving from left to right across a period Ionization Energy Amount of energy needed to remove an efrom an atom to form an ion Decreases moving down a group Increases moving from left to right across a period IONS --> Atoms with a Lithium Ion Lithium Atom charge 3+ 320+1charge charge 3+ The ionization energy is the amount of energy needed to remove this e- Octet rule and ions Atoms with a filled outer energy level (stable octet) are more stable Group Charge of most common ion 1A +1 Atoms lose/gain electrons in an effort to obtain a filled outer energy level. 2A +2 3A +3 4A +4, -4 Anions (- ions) form by an atom gaining e- 5A -3 6A -2 7A -1 Cations (+ ions) form by an atom losing e- 8A Usually do not form ions Electronegativity The ability of an atom to attract electrons in a chemical bond Increases moving from left to right across a period Decreases going down a group