1 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, Majority of figures/tables are from the Ebbing lecture outline. Section 8 Periodic Properties of the Elements

2 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, Majority of figures/tables are from the Ebbing lecture outline. Electron Configuration An “electron configuration” of an atom is a particular distribution of electrons among available sub shells. –The notation for a configuration lists the sub-shell symbols (s, p, d, f) sequentially with a superscript indicating the number of electrons occupying that sub shell. –For example, lithium (atomic number 3) has two electrons in the “1s” sub shell and one electron in the “2s” sub shell 1s 2 2s 1.

3 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, Majority of figures/tables are from the Ebbing lecture outline. The Pauli Exclusion Principle The maximum number of electrons and their orbital diagrams are: Sub shell Number of Orbitals Maximum Number of Electrons s (l = 0)12, s 2 p (l = 1)36, p 6 d (l =2)510, d 10 f (l =3)714, f 14

4 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, Majority of figures/tables are from the Ebbing lecture outline. Aufbau Principle Every atom has an infinite number of possible electron configurations. –The configuration associated with the lowest energy level of the atom is called the “ground state.” –Other configurations correspond to “excited states.

5 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, Majority of figures/tables are from the Ebbing lecture outline. Aufbau Principle The Aufbau principle is a scheme used to reproduce the ground state electron configurations of atoms by following the “building up” order. –Listed below is the order in which all the possible sub-shells fill with electrons. 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f –You need not memorize this order. As you will see, it can be easily obtained from the periodic table.

6 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, Majority of figures/tables are from the Ebbing lecture outline. Configurations and the Periodic Table

7 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, Majority of figures/tables are from the Ebbing lecture outline. Aufbau Principle The “building up” order corresponds for the most part to increasing energy of the subshells. –By filling orbitals of the lowest energy first, you usually get the lowest total energy (“ground state”) of the atom. –Remember, the number of electrons in the neutral atom equals the atomic number, Z. Electron configurations describe e -. –Ca 2+ lost 2e - must account for this –Cl - gained 1e - must account for this

8 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, Majority of figures/tables are from the Ebbing lecture outline. Here are a few examples: Aufbau Principle

9 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, Majority of figures/tables are from the Ebbing lecture outline. Aufbau Principle

10 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, Majority of figures/tables are from the Ebbing lecture outline. Aufbau Principle HW 61 & 62

11 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, Majority of figures/tables are from the Ebbing lecture outline. Configurations and the Periodic Table Valence ElectronsValence Electrons are electrons that reside in the outermost shell of an atom - or in other words, those electrons outside the “noble gas core”. –These electrons are primarily involved in chemical reactions. –Elements within a given group have the same “valence shell configuration.” –This accounts for the similarity of the chemical properties among groups of elements.

12 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, Majority of figures/tables are from the Ebbing lecture outline. Configurations and the Periodic Table –In many cases you need only the configuration of the outer electrons. –You can determine this from their position on the periodic table (only look at s and p blocks in outer shell). –The total number of valence electrons for an atom equals its group number.

13 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, Majority of figures/tables are from the Ebbing lecture outline. Configurations and the Periodic Table Note that elements within a given family have similar configurations. –The Group IIA elements are sometimes called the alkaline earth metals. Beryllium1s 2 2s 2 Magnesium1s 2 2s 2 2p 6 3s 2 Calcium1s 2 2s 2 2p 6 3s 2 3p 6 4s 2

14 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, Majority of figures/tables are from the Ebbing lecture outline. Periodic Properties Recall that periodic law states that when the elements are arranged by atomic number, their physical and chemical properties vary periodically. We will look at three periodic properties: –Atomic radius –Ionization energy –Electron affinity

15 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, Majority of figures/tables are from the Ebbing lecture outline. Periodic Properties Atomic radius –Covalent radius – of atom is ½ distance between the nuclei of two like atoms joined in a molecule. –ionic radius same as above. –Within each period (horizontal row), the atomic radius tends to decrease with increasing atomic number (nuclear charge). –Within each group (vertical column), the atomic radius tends to increase with the period number.

16 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, Majority of figures/tables are from the Ebbing lecture outline. –Why increase down? One factor is the principal quantum number, n. The larger is “n”, the larger the size of the orbital. –Why decrease across? The other factor is the effective nuclear charge, which is the positive charge an electron experiences from the nucleus minus any “shielding effects” from intervening electrons. Two factors determine the size of an atom:

17 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, Majority of figures/tables are from the Ebbing lecture outline. Figure: Representation of atomic radii (covalent radii) of the main- group elements.

18 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, Majority of figures/tables are from the Ebbing lecture outline. Ex. Arrange the following in order of increasing atomic radius: Ca, N, As, F, Ba Cations are smaller than neutral atom: Na + < Na Anions are larger than neutral atom: Cl - > Cl

19 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, Majority of figures/tables are from the Ebbing lecture outline. Ionic Radii

20 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, Majority of figures/tables are from the Ebbing lecture outline. Within an isoelectronic group of ions, the one with the greatest nuclear charge (largest excess of protons) will be the smallest. Ex. Ar, Cl -, Ca 2+, S 2-, K + all have 18e - ; same electron configuration but different number of protons

21 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, Majority of figures/tables are from the Ebbing lecture outline. Periodic Properties Ionization energy –The first ionization energy of an atom is the minimal energy needed to remove the highest energy (outermost) electron from the neutral atom in gaseous state. –For a lithium atom, the first ionization energy is illustrated by: Ionization energy = 520 kJ/mol

22 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, Majority of figures/tables are from the Ebbing lecture outline. Periodic Properties Ionization energy –There is a general trend that ionization energies increase with atomic number within a given period (opposite of atomic radius). –This follows the trend in size, as it is more difficult to remove an electron that is closer to the nucleus (hence, smaller size/larger IE). –Ionization process absorbs energy to pull electron off – endothermic process.

23 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, Majority of figures/tables are from the Ebbing lecture outline. Periodic Properties Ionization energy –The electrons of an atom can be removed successively. The energies required at each step are known as the first ionization energy, the second ionization energy, and so forth. 2 nd IE tends to be larger than 1 st IE because you are dealing with ions (charged species) which make it harder to pull an e - from a charged ion than a neutral species; therefore, more energy will be required. Ionization energy 2 = 7298 kJ/mol

24 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, Majority of figures/tables are from the Ebbing lecture outline. Ex. Arrange the following in order of increasing 1 st ionization energy: As, Ca, O, N

25 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, Majority of figures/tables are from the Ebbing lecture outline. Periodic Properties Electron Affinity –The electron affinity is the energy change for the process of adding an electron to a neutral atom in the gaseous state to form a negative ion. –Electron affinity process releases energy – exothermic process. Electron Affinity = -349 kJ/mol

26 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, Majority of figures/tables are from the Ebbing lecture outline. Periodic Properties Electron Affinity –The more negative the electron affinity, the more stable the negative ion that is formed. –Broadly speaking, the general trend goes from lower left to upper right as electron affinities become more negative. HW 63