Mendeleev Made periodic table based on atomic mass and other properties. (especially chemical) Had blank spots for undiscovered elements Called periodic because properties repeat periodically. (Periodic law)

Henry Mosely Discovered nuclear charge. Gives the “atomic number.” Fixes Mendeleev’s periodic table.

Periodic Table Organized based on properties of elements Not all periodic tables have the same information Shape determined by electronic structure of atom Properties occur in a repeating pattern

Metals, Metalloids, and Nonmetals

Properties of Metals Conduct electricity Conduct heat Malleable Ductile Have luster or sheen tend to make cations by losing electrons

Non Metals  opposite properties of metals – Tend to make anions by gaining electrons Metalloids  properties in between metals and nonmetals

Periodicity The properties of elements repeat in a regular pattern. (groups) This is periodic law. Elements are grouped according to properties Pattern is related to electron configuration. – Group 1 metals all have the same last term in their electron configuration. Li 2s 1 F 2s 2, 2p 5 Na 3s 1 Cl 3s 2, 3p 5 K 4s 1 Br 4s 2, 4p 5 Rb 5s 1 I 5s 2, 5p 5

Groups on the Periodic Table

Periodic properties Atomic radius Ionization energy Ionic radius Electronegativity Nuclear charge Shielding

Nuclear Charge The positive charge on the nucleus. (atomic number) Determined by Henry Moseley in 1913 Trend: Decreases from bottom to top of group. Increases from left to right in a period

Shielding The effect of the surrounding electrons on the nuclear charge. Less shielding causes electrons to be held more tightly. Trend: Decreases from bottom to top of a group Constant across a period

Atomic radius Defined as ½ the distance between the nuclei of 2 atoms of an element when bonded together Trend: decreases from bottom to top of a group Decreases from left the right across period

Ionization energy The amount of energy required to remove an electron from a neutral atom in the gas phase Trend: Increases from bottom to top in a group. Increases from left to right across a period.

Ionization energy

Electron Configuration and Ionization Energy

Ionic radius The radius of the ion in a crystal lattice Trend: Decreases from bottom to top of a group. Decreases for cations across the period. Cations are smaller then the neutral atom. Decreases for anions across the period. Anions are larger than the neutral atom. Cations Anions

Electronegativity The ability of a nucleus to attract the electrons in a bond Trend: Increases from bottom to top of a group. Increases from left to right across a period