1. Period Four
TRENDS

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

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

4. reactivity- ability of an element to undergo chemical changesK
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

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

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

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