Trends in the Periodic Table

Electron Configurations Elements organized according to valence electrons(outer electrons). H=1s1 Li=[He]2s1 Na=[Ne]3s1 K=[Ar]4s1 Elements in a group have similar properties because they have valence electrons in similar configurations. Periodic Table contains s, p, d and f blocks. Electrons filling these orbitals for elements in these groups.

Periodic Trends Many properties of the elements change in a predictable way as you move through the periodic table.

Atomic Radius Distance from center to outermost electrons. Radius increases going down a group. Radius decreases going left to right.

Atomic Radius Why does radius increase as you move across a period? As you move down a group, electrons are in larger principal quantum #’s and are therefore further away. Across a period – outer electrons are in same principal quantum #. All these should be same size but they are not. Why? Increase # of protons in nucleus creates a stronger force of attraction for electrons.

Ionic Size When atoms lose electrons, they become smaller. Li atom = 0.152nm Li+ ion = 0.060nm Vacates largest orbital and reduces repulsive force between remaining electrons.

Ionic Size When atoms gain electrons they become larger. F atom = 0.064nm. F- ion = 0.136nm.

Ionization Energy The energy needed to remove one of an atoms electrons. 8.64x10-19 joules are required to remove 1 electron from a lithium atom. Li(g)  Li+(g) + e- IE = 8.64x10-19 J/atom or 521kJ/mol Measure on atoms in the gas state

Ionization Energy High ionization energy means it holds onto electrons tightly. Two trends: Decrease as you move down a group. Increase as you move from left to right. Opposite of atomic radius – electrons in smaller atoms are held more strongly by the nucleus.

Successive Ionization Energies For each element there is a large increase between a certain pair of ionization energies. Nobel gas inner cores are held more strongly than valence electrons.

Electron Affinity Energy change that occurs when an atom gains an electron. Ne(g) + e-  Ne-(g) EA = 29KJ/mol 29KJ is needed to add an electron to 1 mol of Neon. F(g) + e-  F-(g) EA = -328KJ/mol 328KJ is released when 1 mol of F gain electrons. Atoms with greater attractions for added electrons have more negative EA.

Electronegativity Ability to attract electrons in a chemical bond.