trends in periodic table

Atomic radii
• Ingoing from top to bottom of a group, the outermost electrons are assigned to orbitals with increasingly higher values of the principal quantum number. The underlying electrons require space so the electrons of the outer shell is farther from the nucleus.
• In a period, going across the period, a proton is added to each nucleus and an electron is added to each outer shell. In each, the effective nuclear charge increases slightly because the effect of each additional proton is more important than the effect of an additional electron. The result is the attraction between the nucleus and electrons increase
• Transition metals- from left to right, the radii initially decrease. In the middle, they then slightly increase until the end of the series. It increases slightly because the d subshell is filled and the repulsion cause the size to increase.

Ionization energy- remove an electron
• Separate an electrone energy must be supplied to overcome attraction of nuclear charge (endothermic process, positive values)
• Large jumps in second and third IE is experimental evidence for the electron shell structure of atoms
• Ionization energy for the removal of the second electron is large because the second electron is removed from a much lower energy (inner) subshell
• The trend across a period is rationalized by the increase in effective nuclear charge

Electron Affinity
• The energy of a process in which an electron is acquired by the atom (the greater the affinity, the more negative the value, exothermic reaction)
• An element with a high ionization energy generally has a high affinity for an electron

Ions
• the radius of a cation is always smaller than that of the atom from which it is derived. (the attractive force from the nucleus is no exerted on less negative)
• anions are always larger than the atoms from which they are derived because of more electron-electron repulsion