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PSC Chap. 4 The Periodic Table In modern periodic table, elements in the same column have similar properties. John Newlands - Law of Octaves – arranged first 16 elements in order of atomic mass – found that similar properties were found every 8th element Dmitri Mendeleev - invented the modern periodic system - basis of the modern periodic table – arranged all known elements in order of atomic mass – placed elements w/ similar properties in vertical columns A couple of problems w/ Mendeleev's table • Some elements did not fit into the right columns when put in order of atomic mass. If switched, they fit. – -ex. Te and I, Co and Ni A couple of problems w/ Mendeleev's table • In order to put some elements in the right column, gaps had to be left in his table. • He predicted elements would be discovered to fill the gaps • Also correctly predicted properties of these undiscovered elements Henry Mosely, using X-rays, discovered the atomic number of elements. When elements in Mendeleev's table were placed in order of atomic number, they fell into the right columns. Periodic Law • - the physical and chemical properties of elements are a periodic function of their atomic numbers Period or Series • elements that form a horizontal row in the periodic table • all elements in the same series have the same outer energy level Group or Family • elements that form a vertical column in the periodic table • elements in the same group have similar electron configurations • also have similar properties. Periodic Table can be divided into 2 regions • Metals - left side of table – good conductors of electricity and heat – shiny – malleable – groups 1-12 and some of groups 13-16 • Nonmetals - right side of table – poor conductors of electricity and heat – dull – brittle – some of groups 14 -16 and all of groups 17 & 18 Metalloids • Semiconductors (semi-metals) • Have properties of both metals and nonmetals • lie on dividing line • used to make transistors and computer chips Main-Group Elements • Also called representative elements • s and p block elements • have consistent electron configurations Group 1 • • • • • • Alkali Metals all end in s1 lose the outer e- to form +1 ions Very reactive metals React w/ water and oxygen soft Group 2 • • • • • Alkaline Earth Metals Active metals end in s2 lose 2 outer e-’s to form +2 ions not as soft as group 1 metals Transition Metals • d block elements – highest energy e-’s are in the d sublevel • not as reactive as groups 1 and 2 • have varied properties Lanthanides and Actinides • f block elements – highest energy e-’s are in the f sublevel • sometimes called rare earth elements or inner-transition elements • Lanthanide series fills 4f sublevel – shiny, reactive, irregular configurations Lanthanides and Actinides • Actinide series fills 5f sublevel – radioactive Group 16 • Chalcogens • Contains active nonmetals (top) to metalloids to less active metals • end in s2p4 • nonmetals gain 2 e-’s to form -2 ions Group 17 • • • • • Halogens Most reactive nonmetals react with metals to form salts end in s2p5 gain 1 e- to form -1 ions Group 18 • Noble Gases • Mostly unreactive • end in s2p6 Hydrogen • In a class by itself • Behaves unlike other elements because it has only 1 p+ and 1 e• Most common element in the universe • Properties of elements are determined by their electron configurations. • Elements with similar properties have similar electron configurations. Periodic Trends • Atomic radii • Reactivity Atomic radius • Atomic radius increases as you move down a group – Add an energy level as you move down • Atomic radius decreases as you move across a period – Increased nuclear charge pulls e- cloud in tighter Reactivity of Metals • Metals tend to lose e-’s • As you move down a group, reactivity of metals increases – Atoms are bigger and e-’s are held less tightly • As you move to the left, reactivity of metals increases – atoms are bigger to the left Reactivity of Metals • The most active metal is in the lower left corner of the periodic table. • Fr Reactivity of Nonmetals • Nonmetals tend to gain e-’s • As you move up a group, reactivity of nonmetals increases – Atoms are smaller and hold e-’s more tightly • As you move to the right, reactivity of nonmetals increases (noble gases not considered) – Atoms are smaller Reactivity of Nonmetals • The most active nonmetal is in the upper right corner of the periodic table. • F