15.999 + 1.008 = 56.105. • Number of Electron Pairs Shape Bond Angle Example 2 Linear 180° BeCI 2 3 Trigonal planar 120° 4 Tetrahedral 109.5° ch 4 5 6 Octahedral 90 sf 6 7.5 Molecules with lone pairs occupying equatorial positions) • BrF 5 ? Trigonal bipyramid 90°,120°,180° pci 5 6 7 8 M 9.4.3 Modern Periodic Table 9.1 Historical trends 9.2 Mendeleevs table (1869) 9.3 Modern Periodic Table Atomic Number and X the symbol. E.g. 23 Na This sodium atom contains 11 protons, 11 electrons and.