6.1 Organizing the Elements A few elements, such as gold and copper, have been known for thousands of years - since ancient times Yet, only about 13 had been identified by the year As more were discovered, chemists realized they needed a way to organize the elements. Chemists used the properties of elements to sort them into groups. In 1829 J. W. Dobereiner arranged elements into triads – groups of three elements with similar properties –One element in each triad had properties intermediate of the other two elements

6.1 Organizing the Elements By the mid-1800s, about 70 elements were known to exist Dmitri Mendeleev – a Russian chemist and teacher Arranged elements in order of increasing atomic mass Thus, the first “Periodic Table” He left blanks for yet undiscovered elements –When they were discovered, he had made good predictions

6.1 Organizing the Elements In 1913, Henry Moseley – British physicist, arranged elements according to increasing atomic number The arrangement used today The symbol, atomic number & mass are basic items

6.1 Organizing the Elements When elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties. Horizontal rows = periods –There are 7 periods Vertical column = group (or family) –Similar physical & chemical prop. –Identified by number & letter (IA, IIA)

6.1 Organizing the Elements Three classes of elements are: 1) Metals: electrical conductors, have luster, ductile, malleable 2) Nonmetals: generally brittle and non-lustrous, poor conductors of heat and electricity Some nonmetals are gases (O, N, Cl); some are brittle solids (S); one is a fuming dark red liquid (Br) 3) Metalloids: Properties are intermediate between metals and nonmetals

6.1 Organizing the Elements Section 6.1 Quiz: Identify which of the following groups of elements all have similar physical and chemical characteristics….. a.K, Ca, Rb, Sr b.La, Ce, Pr, Nd c.Li, Be, B, C d.Ne, Ar, Kr, Xe

6.1 Organizing the Elements Section 6.1 Quiz: Identify which of the following groups of elements are all in the same period…. a.Mo, Pd, Ni, Mg b.Na, Li, K, Fr c.N, O, F, Ne d.Mg, Al, Ge, S

6.1 Organizing the Elements Section 6.1 Quiz: Identify which of the following groups of elements are all in the same family (group)….. a.B, Al, Ga, In b.F, Ne, Cl, Ar c.Na, Mg, Al, Si d.K, Ca, Rb, Sr

6.1 Organizing the Elements Section 6.1 Quiz: Identify which of the following groups of elements are all metals… a.K, Ca, Rb, Sr b.La, Ce, Se, Br c.Li, Be, B, C d.Ne, Ar, Kr, Xe

6.1 Organizing the Elements Section 6.1 Quiz: Identify which of the following groups of elements are all without a luster or shine…. a.K, In, At, Rn b.Ca, Ga, P, F c.I, Br, Xe, Rn d.Ne, Cl, Al, Cr

6.1 Organizing the Elements Section 6.1 Quiz: Identify which of the following groups of elements are all metalloids….. a.Al, Si, Ga, Sb b.B, Si, As, Te c.B, Ge, Sn, Po d.Bi, Sn, Ga, Zn

6.1 Organizing the Elements Section 6.1 Quiz: Identify which of the following groups of elements are all gasses….. a.N, O, F, P b.H, He, Kr, Rn c.Hg, Br, C, O d.Al, N, O, F

6.1 Organizing the Elements Section 6.1 Quiz: Identify which of the following groups of elements all conduct electricity….. a.K, Ca, Rb, Sr b.La, Ce, S, Ar c.Li, Be, B, F d.Ne, Ar, Kr, Xe

6.1 Organizing the Elements Section 6.1 Quiz: Identify which of the following groups of elements are all malleable and ductile….. a.Cs, At, Rn, Br b.Mg, As, Br, Xe c.Fe, Co, Mo, Tc d.Mg, Mn, Po, Cl