Period Four TRENDS

Atomic Mass- mass of an atom K 39.10amu Ca 40.08amu Ga 69.72amu Ge 72.64amu As 74.92amu Se 78.96amu Br 79.90amu Kr 83.79amu

Atomic size- radius of an atom K 243pm Ca 194pm Ga 136pm Ge 125pm As 114pm Se 103pm Br 94pm Kr 88pm

reactivity- ability of an element to undergo chemical changes K Reacts violently with water Ca Reacts with water Ga Does not react with oxygen Ge Reacts very slowly with oxygen As Se Reacts slowly with metals Br Reacts vigorously with metals Kr Unreactive

Shielding effect- full core shells blocking the positive nuclear force from reaching the valence shell K 18 Ca Ga Ge As Se Br Kr

Ionization energy- energy required to remove an electron K 420 Ca 590 Ga 580 Ge 780 As 960 Se 950 Br 1140 Kr 1350

Electronegativity- tendency of an atom to attract electrons K 0.8 Ca 1.0 Ga 1.6 Ge 1.8 As 2.0 Se 2.4 Br 2.8 Kr --