4 Trends in Atomic Radii Decrease across the period Due to increasing positive charge of the nucleusIncrease as you go down the groupException Ga to Al – Ga smaller due to increased nuclear charge (first addition of d electrons)
5 ProblemsWhich of these elements; Li, Rb, K or Na has the smallest radius? Largest?Which of these elements; O, Se, S and Po has the smallest atomic radius? Largest?
6 Ionization Energy Atom + energy → Atom+ + e- First electron removed – First Ionization Energy (IE1)Second electron removed – Second Ionization Energy (IE2) etc.Group 1 – lowest ionization energyGroup 18 - highest ionization energyIonization energies increase across the period due to increased nuclear charge.Ionization energies decrease down a group due to further distance from nucleus and electron shielding
10 Why? Each successive electron feels a stronger nuclear attraction This information lead to the understanding of the stability of the noble gas configuration+
11 Practice Choose the element with the higher IE1: Ca or Ba Ca or Br Ca or KCa or Mg
12 Electron Affinity Atom + e- → Atom- + (- energy) IMPORTANT!!!!! Negative energy means energy lost by systemPositive energy means energy gained by systemSign indicates direction not numerical value!!!!
14 Electron Affinity Trends Generally become larger (look at as absolute value) as you move across the period.Exception – Group 15 due to half filled p orbitalsGenerally become smaller as you move down a group due to:Greater Nuclear AttractionGreater Atomic Radius
15 Second Electron Affinities Very difficult to add an electron to an anion (negative ion)Second Electron Affinities are all positive
16 Ionic Radii Cation (positive ion) Anion Smaller atomic radius than atomDue to:electrons being removedincreased effective nuclear chargeAnionLarger atomic radius than atomDue toelectrons being addeddecreased effective nuclear chargeGreater repulsion of electrons
18 Valence ElectronsAvailable to be lost, gained or shared when compounds are formed.In outer main energy levelsFor Main Group Elements – s and p orbitals
19 Bonded Atoms Very rarely are electrons shared equally Usually attracted more to one atomThis will effect the chemical properties of the compound!!!Measure of attraction – called electronegativityBased on a 4.0 scale – F = 4.0.Developed by Linus Pauling
21 Electronegativity Trends Increase across a period.Tend to decrease or stay the same down a group.If a noble gas does not form compounds – it does not have an electronegativityIf a noble gas does form compounds – it will have a high electronegativity
24 D-BlockThese elements tend to vary less and with less regularity than Main Group Elements.Still electrons in d orbitals are often responsible for characteristics of elements in the d-blockAtomic radius tends to decrease across the blockIonization energies generally increase across both the d and f-blocks
25 D and F Blocks Tend to lose electrons from outer shell!!!! That means the valence electrons come from the ns shell not the (n-1)d shellGenerally these elements from 2+ ions.ElectronegativitiesD-block - between 1.1 and 2.54 (Only groups 1 and 2 are lower)F-block – between 1.1 and 1.5