Periodicity-trends of the elements on the

periodic tableMr. Guerrero LFHS

The 2 reasons for most trends:• 1) Effective Nuclear Charge(Zeff)-the ability(pull) of the nucleus to attract its

valence electrons. This increases with increasing numbers of protons in the nucleus.

• The Zeff is explained by Colomb’s Law: Where K = 8.99 x 109 N m2/C2

•

• 2) Shielding Effect-the interference on effective nuclear charge by core electrons. This effect increases as energy levels increase. Shielding has no effect along a period, only within groups!

Periodic Trend #1:

• Atomic Radius- ½ the distance between the nuclei of two identical bonded atoms.

•

• Trend Atomic Radius increases toward He.

Ionic Radius-size of cation or anionLEO/GER

Arrange by increasing atomic radius

•Al, Sr, F, P, Ba

•K+, K, N3-, Mg, Mg2+, Ca2+, Na, Na+

Why do d-orbitals have n-1

• Penetration effect- the effect whereby a valence electron penetrates the core electrons, thus reducing the shielding effect and increasing the pull from the nucleus. (The electron is temporarily closer to the nucleus than normal.) • most penetration ns>np>nd>nf least penetration This means that the

s electrons “penetrate” or come closer to the core more often than do p, d, or f electrons. • Electrons fill orbitals in order of increasing energy. Because of the

penetration effect, electrons fill (n+1)s before nd. ((n+1)s has lower energy). For example, 4s fills before 3d.

Electronegativity- the attraction of a nucleus for electrons. Trend: electronegativities increase toward Fluorine• Arrange by decreasing electronegativity:

Cs, Si, F, Ca, Ga

Electron Affinity (electron loving)• Electron Affinity- the energy change associated when an atom, in the

gaseous state gains an electron. Electron affinity values are always negative.

•Rxn: X(g) + e- X-(g) DE = ????

• Trend: same as electronegativity

First Ionization Energy• First Ionization Energy – The energy required to remove the first

electron from a neutral atom, in the gaseous state.

• Rxn: X(g) X+(g) + e-

DE = ????

Trend: Valence electrons in smaller atoms are harder to remove, because they are closer to the nucleus.

Therefore: He has the highest Ionization energy!

Middle of the p-block exception: Exceptions to the rule

Ionization energy and electron affinity have several examples of exceptions. This includes exceptions within the p-block that you are responsible for knowing. Atomic radius and electronegativity do not have as many exceptions, and none are notable enough that you must know.

p-block exceptions: e- affinity & 1st Ioniz. E.-As e-’s fill the p-block, the 4th e- must enter the first occupied orbital. The previous e- causes a large e-/e- repulsion, which causes an anomaly in ionization energy and electron affinity trends.

Ionization energy actually drops between group2-13(Be-B) AND groups 15-16(N-O)

Use arrows to show the increase in: electronegativityatomic radiuse- affinityfirst ionization energy

Second Ionization energy(IE2)- the energy required to remove the second electron from a neutral atom, in the gas phase.

• After the removal of each electron, the electrons get closer to the nucleus, due to less e-/e- repulsion.• The energy required to remove the next electron is always greater

than the energy required to remove the previous electron.

IE1 < IE2 <IE3 < IE4….

1 2 3 4 5 6 7 8

H 1312

He 2372 5250

Li 520 7297 11810

Be 899 1757 14845 21000

B 800 2426 3659 25020 32820

C 1086 2352 4619 6221 37820 47260

N 1402 2855 4576 7473 9442 53250 64340

O 1314 3388 5296 7467 10987 13320 71320 84070

F 1680 3375 6045 8408 11020 15160 17860 92010

Ne 2080 3963 6130 9361 12180 15240

Na 496 4563 6913 9541 13350 16600 20113 25666

Mg 737 1450 7731 10545 13627 17995 21700 25662

Ionization Energies in kJ/mol

• Work out AP released 2007, form B, #6

Polarizability-the distortion of a nonpolar electron cloud to a temporary dipole, by the presence of a near by atom.

• As the total number of electrons increases, polarizability also increases.