1CHAPTER 6| Chemical Periodicity2Electronic Structure and the Periodic Table | The electron configuration of the elements falls into four blocks (s, p, d, f) in the periodic table.z Helium belongs to the s-subshell but is noted above the p-subshell block on the periodic table. • It does not share the same chemical & physical properties of the elements in the s-subshells.z Hydrogen belongs to the s-subshell, but has properties more similar to the elements in the p-subshell block.3Electronic Structure and the Periodic Table| Noble Gases (rare gases)z All of them have completely filled electron shells.| Since they have similar electronic structures, their chemical reactions are similar.z He 1s2z Ne [He] 2s22p6z Ar [Ne] 3s23p6z Kr [Ar] 4s24p6z Xe [Kr] 5s25p6z Rn [Xe] 6s26p64Electronic Structure and the Periodic Table| Representative Elements (Main Group)z Are the elements in A groups on periodic chart.| These elements will have their “last” electron in an outer s or p orbital.| These elements have fairly regular variations in their properties.5Electronic Structure and the Periodic TableGroup IA, IIA, IIIA Æ form the main group metalsGroup IVA, VA, VIA, VIIA Æform the main group nonmetalsGroup VIIIA Æ noble gases (inert and exist as single atoms)6Electronic Structure and the Periodic Table• d-Transition Elements– Elements on periodic chart in B groups.– Sometimes called transition metals.• Each metal has d electrons.–ns (n-1)d configurations• These elements make the transition from metals to nonmetals.• Exhibit smaller variations from row-to-row than the representative elements.7Electronic Structure and the Periodic Table• f - transition metals– Sometimes called inner transition metals.• Electrons are added to forbitals.• Electrons are added two shells below the valence shell!• Consequently, very slight variations of properties from one element to another.8Electronic Structure and the Periodic Table| Outermost electrons have the greatest influence on the chemical properties of elements.| The group number in the main groups indicates the number of valence-shell electrons of elements in the group.z Group IA elements have 1 electron in their valence-shell 1s1,2s1,3s1, 4s1, 5s1, 6s1, 7s1z Group IIA elements have 2 electrons in their valence-shell 1s2, 2s2, 3s2, 4s2, 5s2, 6s2, 7s2z Group III A elements have 3 electrons in their valence-shellns2np1z Group VA elements have 5 electrons in their valence-shellns2np39Periodic Properties of the Elements| The periodic table is useful in determining different properties of elements that:z Help us understand and predict chemical bondingz Help us understand and predict certain trends associated with the organization of the elements on the table10p.236Atomic radii describes the relative sizes of atoms.The atomic radius of an element is defined as half the distance between the nuclei of neighboring atomsPeriodic Properties of the ElementsIf the element is nonmetal or metalloid; the distance between nuclei joined by chemical bond (covalent radius)Atomic radii is determined by measurement of the distance between the nuclei of homonuclear molecules, e.g., Cl2 (198 x 10−12 m Æ 198 pm)11| Atomic radii increase within a column going from the top to the bottom of the periodic table.| Atomic radii decrease within a row going from left to right on the periodic table.z This last fact seems contrary to intuition.z How does nature make the elements smaller even though the electron number is increasing?Periodic Properties of the Elements12Atomic Radii (Section 1.14)The atomic radii trend:Slide 7 p.23813Atomic RadiiThe reason the atomic radii decrease across a period is due to shielding or screening effect.z Effective nuclear charge, Zeff, experienced by an electron is less than the actual nuclear charge, Z.z The inner electrons block the nuclear charge’s effect on the outer electrons by repulsion.• Each electron, in an atom with many electrons, is repelled by the other electrons.• The outer electrons are shielded by the inner electrons from the full attraction of the nucleus.14Periodic Properties of the ElementsFigure 1.40 Effective Nuclear Charge15Atomic Radii• nuclear charge is the positive charge of the nucleus• the size of an atom is determined by the effective nuclear charge• shielding electrons are the filled energy levels of an atom and they tend to shield the outer electrons from feeling the full attraction of the nucleus.The one valence electron (2s1) does not feel the full effect of the 3+ nucleus1s22s1Li has two shielding electrons (1s2)3+16Figure 12.38: Atomic radii (in picometers) for selected atoms.Zeffincreases Zeff decreasesThe effective nuclear charge increases across the periods. Consequently, the outer electrons feel a stronger effective nuclear charge. As electrons are added to more energy levels, the size of the atom increases.17Atomic Radii| Arrange these elements based on their increasing atomic radii.z Se, S, O, TeO < S < Se < Tez P, Cl, S, SiCl < S < P < Siz Ga, F, S, AsF < S < As < Ga18Ionic Radius• The ionic radius of an element is the distance between the radii of the ions in an ionic solid (ionic crystal).19Ionic Radii Cations (positive ions) are always smaller than their respective neutral atoms.Element Li NaAtomic Radius (Å)1.52 1.86Ion Li+Na+Ionic Radius (Å)0.90 1.1620p.244Cations (positive ions) are always smaller than their respective neutral atoms.Anions (negative ions) are always larger than their respective neutral atoms.Ionic Radii21Ionic Radii• Anions (negative ions) are always larger than their neutral atoms.Element N O FAtomicRadius(Å)0.75 0.73 0.72Ion N3−O2−F−IonicRadius(Å)1.71 1.26 1.1922Ionic RadiiAn isoelectronic series consist of ions that have the same number of electrons. The Zeff has a more obvious effect on the metal ions.23Ionic RadiiNote: This trend is generalized to metal ions and nonmetals ions separately.24Ionic Radii Cation (positive ions) radii decrease from left to right across a period.– Increasing nuclear charge attracts the electrons and decreases the radius.Ion Rb+Sr2+In3+IonicRadii(Å)1.66 1.32 0.9425Ionic Radii Anion (negative ions) radii decrease from left to right across a period.– Increasing electron numbers in highly charged ions cause the electrons to repel and increase the ionic radius.Ion N3-O2-F1-IonicRadii(Å)1.71 1.26 1.1926Ionic RadiiArrange these elements based on their increasing ionic radii.z Ga, K, CaGa3+ <