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

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

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

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

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.

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

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

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

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

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)

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

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

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

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

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

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

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

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