History, Groups, and Info on the Periodic Table

1. History, Groups, and Info on the Periodic Table 9/4/08

2. Part I: History of the PT • by 1860, more than 60 elements had been discovered (this is almost 40 years before the Thomson model debuted). • however, there was no uniform way established to measure atomic masses accurately, and therefore… • chemical formulas were almost impossible to determine correctly. • September 1860—Germany—group of chemists assembled to settle the issue of atomic mass (and other misunderstood atomic matters). • Cannizarro, Stanislao—presented accurate method to measure atomic mass. • Mendeleev, Dimitri—1869—used this new information to organize and arrange the elements (this is the 1st time it was attempted). Almost a Decade Later Cannizarro

3. Mendeleev, Dimitri—1869—used this new information to organize and arrange the elements (this is the 1st time it was attempted). • arranged the elements according to known properties and in order of increasing atomic weight • he noticed a trend—by arranging elements in 6 rows, he noticed a repeat in their properties down each column (this is known as a periodic pattern). Mendeleev

4. he noticed a trend—by arranging elements in 6 rows, he noticed a repeat in their properties down each column (this is known as a periodic pattern). • some elements had not yet been discovered, so he left spaces for them. He also predicted what properties these undiscovered elements would have. • later on, the elements that would fit in those spaces were discovered, and their properties matched what he predicted. • some discrepancies existed (iodine and tellurium).

5. Moseley, Henry—1911—used Mendeleev’s PT to write the periodic law. • periodic law: the physical and chemical properties of the elements are periodic functions of their atomic numbers. • he arranged elements in order of atomic number, not weight. • Today’s PT is arranged by atomic number, thanks to Moseley. Part II: Groups of the PT • on the PT, a horizontal row is called a period, and a vertical column is a group. • sometimes, other parts (other than single columns) are referred to as “groups.” • each group of the PT shares similar chemical and physical properties. • intensity of these properties tends to increase down a group. Moseley

6. each group of the PT shares similar chemical and physical properties. Family Period

7. alkali metals = very reactive with most substances, especially water and air. Form oxides easily, have a silvery appearance. Soft in pure form —can be cut with knife. Stored under kerosene or mineral oil. (e- config ends in s1) Na Na reacting with H2O alkali metals

8. alkaline-earth metals = not as reactive as alkali metals. Harder, denser, and stronger. Have higher melting points. Form alkaline solutions when dissolved in water (pH >7). (e- config ends in s2) Mg Ba in oil alkali metals alkaline-earth metals

9. transition metals= good conductors of electricity and heat. High luster. Less reactive than first 2 groups. Some exist as free elements (Pd, Pt, Au, Cu, Ag). Ductile (can be pulled into a wire), malleable (can be hammered, rolled into thin sheets). (e- config ends in d1-10) Mn alkali metals alkaline-earth metals transition metals Cu

10. The p-block is divided into three types of elements: • p-block metals: elements below the metalloid line. Very similar to the s- and d-block metals. • nonmetals: elements above the metalloid line. Are brittle, non-conductors, some gases (includes H). Ga nonmetals alkali metals alkaline-earth metals p-block metals transition metals P

11. metalloids: on the metalloid line = B, Si, Ge, As, Sb, Te. Have properties of metals and nonmetals. Semiconductors. • halogens = highly reactive nonmetals. React with metals to form salts. Used in halogen lighting.(e-config ends in s2p5) Si nonmetals metalloids halogens alkali metals alkaline-earth metals p-block metals I transition metals

12. noble gases: unreactive. Very rarely form compounds with any element. Used in neon signs. (e-config ends in s2p6) • lanthanides = top row of f-block. Very similar in chemical properties. Mostly natural. (e-config ends in 6s24f1-14). • actinides = bottom row of f-block. Very similar in chemical properties. Mostly synthetic. Some used in nuclear chemistry. (e-config. ends in 7s25f1-14). Xe Nd nonmetals metalloids noble gases halogens alkaline-earth metals alkali metals p-block metals U transition metals lanthanides actinides