1. Periodic Table It is a systematic catalog of the elements. Elements are arranged in order of atomic number.

2. Periodicity When one looks at the chemical properties of elements, one notices a repeating pattern of reactivities.

3. Periodic Table The rows on the periodic chart are periods. Columns are groups. Elements in the same group have similar chemical properties.

4. Groups These five groups are known by their names.

5. Periodic Table Nonmetals are on the right side of the periodic table (with the exception of H). Gases – Group 18 and F, O, N, H, Cl Liquid – Br Rest are solids

6. Periodic Table Metalloids border the stair-step line (with the exception of Al, Po, and At).

7. Periodic Table Metals are on the left side of the chart. Properties – luster and high electrical and heat conductivity malleable All except Hg are solids at room temperature

8. Development of Periodic Table Elements in the same group generally have similar chemical properties. Physical properties are not necessarily similar, however.

9. Development of Periodic Table Dmitri Mendeleev and Lothar Meyer independently came to the same conclusion about how elements should be grouped.

10. Development of Periodic Table Mendeleev, for instance, predicted the discovery of germanium (which he called eka-silicon meaning under silicon) as an element with an atomic weight between that of zinc and arsenic, but with chemical properties similar to those of silicon.

11. Development of Periodic Table  1913 – Henry Mosley developed concept of atomic number  Bombarded different elements with high-energy electrons, found each element produced X-rays of a unique frequency and that the frequency generally increased with the atomic mass  He arranged the X-ray frequencies in order by assigning them a whole number and called it the atomic number  He correctly identifies the atomic number as the number of protons in a nucleus

12. Development of Periodic Table Concept of atomic number clarified some problems in the periodic table Ex) atomic weight of Ar (18) is greater than that of K (19) yet the chemical properties of Ar are much more like those of Ne and Kr than those of Na and Rb When elements are arranged by atomic number, rather than increasing atomic weight, Ar and K appear in the correct places This made is possible to discover previously unknown elements

13. Periodic Trends In this chapter, we will rationalize observed trends in – Sizes of atoms and ions. – Ionization energy. – Electron affinity.