History of the Periodic Table Dimitri Mendeleev published a periodic table that arranged elements by increasing atomic mass Dimitri Mendeleev published a periodic table that arranged elements by increasing atomic mass This did not accurately group elements by similar properties This did not accurately group elements by similar properties The modern table is arranged by increasing atomic number 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 number Periodic Law – there is a periodic repetition of physical and chemical properties when elements are arranged by increasing atomic number Some of Medeleev’s work (1869)

Periodic Table (a review) Groups go down the table Groups go down the table Elements in the same group have similar properties Elements in the same group have similar properties Periods go across the table Periods go across the table Chemical properties of the elements change in a predictable manner going across a period Chemical properties of the elements change in a predictable manner going across a period

Periodic Table review (cont) Group 1A – alkali metals Group 1A – alkali metals Group 2A – alkaline earth metals Group 2A – alkaline earth metals Group 6A - chalcogens Group 6A - chalcogens Group 7A – halogens Group 7A – halogens Group 8A – noble gases Group 8A – noble gases Metals are to the left of the staircase Metals are to the left of the staircase Non-metals are to the right of the staircase Non-metals are to the right of the staircase Metalloids are along the staircase (B, Si, Ge, As, Sb, Te, Po) Metalloids are along the staircase (B, Si, Ge, As, Sb, Te, Po)

Periodic Trends Atomic radius Atomic radius Ionization energy Ionization energy Electronegativity Electronegativity

Atomic Radius The size (radius) of an atom of that element The size (radius) of an atom of that element Increases moving down a group Increases moving down a group Decreases moving from left to right across a period Decreases moving from left to right across a period

Ionization Energy Amount of energy needed to remove an e - from an atom to form an ion Amount of energy needed to remove an e - from an atom to form an ion Decreases moving down a group Decreases moving down a group Increases moving from left to right across a period Increases moving from left to right across a period

IONS --> Atoms with a charge charge Lithium Atom charge Lithium Ion 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 Atoms with a filled outer energy level (stable octet) are more stable Atoms lose/gain electrons in an effort to obtain a filled outer energy level. Atoms lose/gain electrons in an effort to obtain a filled outer energy level. Anions (- ions) form by an atom gaining e - Anions (- ions) form by an atom gaining e - Cations (+ ions) form by an atom losing e - Cations (+ ions) form by an atom losing e - GroupCharge of most common ion 1A+1 2A+2 3A+3 4A+4, -4 5A-3 6A-2 7A 8AUsually do not form ions

Electronegativity The ability of an atom to attract electrons in a chemical bond The ability of an atom to attract electrons in a chemical bond Increases moving from left to right across a period Increases moving from left to right across a period Decreases going down a group Decreases going down a group