History of the Periodic Table

1. History of the Periodic Table • Dimitri Mendeleev published a periodic table that arranged elements by increasing atomic mass • This did not accurately group elements by similar properties • 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 Some of Medeleev’s work (1869)

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

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

4. Periodic Trends • Atomic radius • Ionization energy • Electronegativity

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

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

7. IONS --> Atoms with a charge Lithium Ion Lithium Atom 3+ 3- 2- 0 charge +1 charge 3+ The ionization energy is the amount of energy needed to remove this e-

8. Octet rule and ions • 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. • Anions (- ions) form by an atom gaining e- • Cations (+ ions) form by an atom losing e-

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