1. 5-3: Electron Configuration & Periodic Properties
Objectives:
Define atomic and ionic radii, ionization energy, electron affinity, and electronegativity
Compare the periodic trends of atomic radii, ionization energy, and electronegativity, and state the reasons for these variations
Define valence electrons, and state how many are present in atoms of each main-group element
Compare the atomic radii, ionization energies, and electronegativity of the d-block elements with those of the main-group elements

2. Atomic Radii
Atomic radius: one-half the distance between the nuclei of identical atoms that are bonded together
Period Trends
Atomic radii decrease from left to right across a period
Trend is caused by the increasing positive charge of the nucleus
Group Trends
In general, the atomic radii of the main-group elements increase down a group
As electrons occupy the sublevels in successively higher main energy levels located farther from the nucleus, the sizes of the atoms increase

3. Atomic radii decreases from left to right across a period and increases down a group

4. Atomic Radius vs. Atomic Number
Plot of atomic radius versus atomic number shows period and group trends

5. Sample Problem
Of the elements magnesium, Mg, chlorine, Cl, sodium, Na, and phosphorus, P, which has the largest atomic radius? Explain your answer in terms of trends in the periodic table.
1. Find the elements listed in the periodic table.
2. Put the elements in order and determine the trend.
Sodium, Na.
Because atomic radii decreases across a period.
Of the elements calcium, Ca, beryllium, Be, barium, Ba, and strontium, Sr, which has the largest atomic radius? Explain your answer in terms of trends in the periodic table.
Barium, Ba.
Because atomic radii increases down a group.

6. You Try!
Of the elements Li, O, C, and F, identify the one with the largest atomic radius and the one with the smallest atomic radius.
Answer: largest: Li ; smallest: F
Of the elements Br, At, F, I, and Cl, identify the one with the smallest atomic radius and the one with the largest atomic radius.
Answer: smallest: F ; largest: At

7. Ionization Energy
An electron can be removed from an atom if enough energy is supplied
Process can be expressed as follows for an atom of any element:
A + energy  A+ + e-
Ion: an atom or group of bonded atoms that has a positive or negative charge
Positive ion = removal of electron
Negative ion = addition of electron
Ionization: any process that results in the formation of an ion
Ionization energy (IE) (or first ionization energy, IE1): the energy required to remove one electron from a neutral atom of an element
Indication of how strongly an atom’s nucleus holds onto its electrons

8. Period Trends Group Trends
Ionization energy generally increases as you move across each period
Trend caused by the increase nuclear charge
 a higher charge more strongly attracts electrons in the same energy level
Group Trends
Ionization energies generally decreases down the groups
Trend caused by an increase in atomic size as you move down a group
 with outer electrons farther from the nucleus, it requires less energy to remove them

10. Electron Affinity
Electron affinity: the energy change that occurs when an electron is acquired by a neutral atom
Most atoms release energy when they acquire an electron
A + e-  A- + energy
Quantity of energy released noted with a negative number
Some atoms must be “forced” to gain an electron by the addition of energy
A + e- + energy  A+
Quantity of energy absorbed noted with a positive number
Ion produced this way will be unstable and will lose the added electron spontaneously

11. Period Trends Group Trends
In general, as electrons add to the same p sublevel of atoms with increasing nuclear charge, electron affinities become more negative across each period within the p block
Halogens gain electrons most readily
Group Trends
Trends within group not as regular; electron affinities change little moving down a group
General rule: electrons add with greater difficulty down a group
Pattern due to increase in nuclear charge down a group (increases electron affinity) and increase in atomic radius down a group (decreases electron affinity)

12. Ionic Radii Cation: positive ion Anion: negative ion
Formation by the loss of one or more electrons
Leads to a decrease in atomic radius because the removal of the highest-energy-level electrons
Remaining electrons are drawn closer to the nucleus by its unbalances positive charge
Anion: negative ion
Formation by the addition of one or more electrons
Leads to an increase in atomic radius
Electron cloud spreads out due to greater repulsion between the increased number of electrons

13. Period Trend Group Trends
Metals to the left tend to form cations and the nonmetals at the upper right tend to form anions
In general, as you move left to right across a period, the size of the positive ions gradually decreases
Cation radius decreases across a period due to the electron cloud shrinking
Caused by increase nuclear charge acting on the electrons in the main energy level
Group Trends
Gradual increase in ionic size as you move down a group
Trend caused by the outer electrons in both cations and anions being in higher energy levels

16. Valence Electrons
Valence electrons: the electrons available to be lost, gained, or shared in the formation of chemical compounds
Chemical compounds form because electrons are lost, gained, or shared between an atom

17. Electronegativity
Electronegativity: measure of the ability of an atom in a chemical compound to attract electrons
Valence electrons hold atoms together in chemical compounds

18. Period Trends Group Trends
Electronegativities tend to increase across each period, although there are exceptions
Group Trends
Electronegativities tend to either decrease down a group or remain about the same

19. Noble gases are unusual in that some of them do not form compounds and cannot be assigned electronegativities
The lowest electronegativities are found at the lower left side of the periodic table, while the highest electronegativities are found at the upper right

20. Periodic Properties of the d- and f-Block Elements
Properties of the d-block element vary less and with less regularity than those of the main-group elements
Difference is due to the presence of electrons in incompletely filled d sublevels in the atoms of the d-block elements

21. 5-3 Classwork
What happens to the atomic radius of an atom in the formation of (a) cation? (b) an anion?
Rank the following elements in order by decreasing atomic radius:
Se, O, Te, S
N, O, Li, B
K, Rb, Li, Cs
As, P, N, Sb
Rank the following elements in order by increasing ionization energy:
Ne, N, C, O
Se, S, Te, O
Ca, Be, Mg, Sr
Rb, Li, Na, K
Which set of elements are not usually assigned a value for electronegativity?
Rank the following elements in order by decreasing electronegativity:
C, N, B, F
At, Br, F, Cl
Br, Ca, Se, K
Rb, Cs, Na, Li