Section 4.6 Periodic Trends of the Elements Section 4.6 Periodic Trends of the Elements Supplemental packet page 58 Periodic Trends increasing trends atomic size electronegativity,EN ionization energy acidity 1 Supplemental packet page 29 Lewis Electron-dot Symbols - A Periodic Trend G.N. Lewis, at the University of California at Berkeley devised a simple way to understand the nature of the chemical bond in both ionic and molecular compounds. His method rests upon focusing on the valence electrons of the elements. He represents these valence electrons as "dots" around the four sides of the elemental symbol. It is the valence electrons (outermost electrons) that are involved in most chemical reactions. Therefore, these Lewis electron-dot symbols should help us understand the chemical properties of these elements. Recall, for these representative elements, group number equals the number of valence electrons, except of helium. Supplemental packet page 29 Electron Dot Structure = Group Number = Valence Electron (outermost) Lewis Dot Structures Group 1 2 3 4 5 6 7 8 H He Li Be B C N O F Ne 1VE Na Mg Al Si P S Cl Ar 8VE • • H 2VE 3VE 4VE 5VE 6VE 7VE He • • • • • • • • • • • • • • • • • • • • • Li Be B •C • • N • •O • •F • Ne • • • • • • • • • • • • • • • • • • • • • • • • • Na • Mg • Al • • Si• • P • •S • •Cl Ar • • • • • • • • • Outermost valence electrons provide chemical reactivity 2 Supplemental packet page 49 Atomic Structure Atomic Number: 11 Physical Properties: Atomic Number: 17 Physical Properties: Name: sodium-23 • • soft metal, Name: 23 • conducts e- Symbol: • • • Symbol: • Na • • • 11 • Chemical Chemical mass # 23 • • Properties: mass # 35 Properties: reacts w/ H O # p ______11 2 # p ______ # n ______12 # n ______ Lewis Dot: Lewis Dot: # e ______11 # e ______ Electronic Na• Electronic Configuration: 1s2 2s2 2p6 3s1 Configuration: Atomic Number: 12 Physical Properties: Atomic Number: 8 Physical Properties: ductile metal, Name:magnesium-24 • • Name: 24 • conducts e- Symbol: • • • • Symbol: • 12Mg • • • • Chemical Chemical mass # 24 • • Properties: mass # 16 Properties: burns in O # p ______12 2 # p ______ # n ______12 # n ______ Lewis Dot: Lewis Dot: # e ______12 # e ______ Electronic 1s2 2s2 2p6 3s2 • Mg• Electronic Configuration: Configuration: Supplemental packet page 49 Atomic Structure Atomic Number: 11 Physical Properties: Atomic Number: 17 • • Physical Properties: Name: sodium-23 • • soft metal, Name: chlorine-35 • • yellow gas, 23 • conducts e- • nonconductor Symbol: • • • Symbol: 35 • • • • 11Na • • • Cl • • • • Chemical 17 • • Chemical mass # 23 • • Properties: mass # 35 • • Properties: reacts w/ H O • • # p ______11 2 # p ______17 reacts w/ Na(s) # n ______12 # n ______18 11 Lewis Dot: Lewis Dot: # e ______ # e ______17 • • Electronic Na• Electronic •Cl• Configuration: 1s2 2s2 2p6 3s1 Configuration: 1s2 2s2 2p6 3s2 3p5 • • Atomic Number: 12 Physical Properties: Atomic Number: 8 Physical Properties: ductile metal, colorless gas, Name:magnesium-24 • • Name: oxygen-16 • • 24 • conducts e- 16 • nonconductor Symbol: Mg • • • • Symbol: • • • 12 • • • 8O • Chemical • Chemical mass # 24 • • Properties: mass # 16 • • Properties: burns in O supports # p ______12 2 # p ______8 combustion # n ______12 # n ______8 12 Lewis Dot: 8 Lewis Dot: # e ______ # e ______ • • Electronic Electronic 1s2 2s2 2p6 3s2 • Mg • 1s2 2s2 2p4 • O• Configuration: Configuration: • • 3 Atomic Radii Supplemental packet page 59 Below is a diagram showing the relative size of atoms. the atoms sizes are in picometers (1 pm = 1EE-12 m). • Two factors must be taken into consideration in explaining this periodic trend (1) Increasing nuclear charge, Z, which is related to the number of increasing protons with a nucleus. • Along a period (left to right) the the atomic number increases while the valence electrons remain in the same shell. Thus due to the increasing nuclear charge (pulling electrons closer to the nucleus) the radii of the atoms decrease left to right. (2) Increasing number of shells, which is related to increasing principal quantum number n, where an element’s row number equals its total number of electrons shells. • Top to bottom along a group the atomic number continues to increase. However the shell increases from shell 1 to shell 2 etc.. The atomic orbitals for each successive shell get larger and larger - more than compensating for the increased nuclear charge. The result is atomic radii increase top to bottom along a group. Supplemental packet page 59 Atomic Radius Variation in the Periodic Table Z=nuclear charge Z increases from left to right within a row Note: atomic size decreases within a row as Z increases see graph 4 Supplemental packet page 50 Ionic Structure Atomic Number: 11 Physical Properties: Atomic Number: 17 Physical Properties: sodium-23 ion Name: • • metal cation Name: 23 1+ • positive ion Symbol: Na • • • Symbol: • 11 • • 1+ charge • Chemical Chemical mass # 23 • • Properties: mass # 35 Properties: combines w/ # p ______11 More protons than # p ______ anions # n ______12 electrons # n ______ Lewis Dot: Lewis Dot: # e ______10 # e ______ Electronic [Na]1+ Electronic Configuration: 1s2 2s2 2p6 3s0 Configuration: Atomic Number: 12 Physical Properties: Atomic Number: 8 Physical Properties: magnesium-24 ion metal cation Name: • • Name: 24 2+ • positive ion Symbol: Mg • • • Symbol: • 12 • • 2+ charge • Chemical Chemical mass # 24 • • Properties: mass # 16 Properties: combines w/ # p ______12 More protons than # p ______ anions # n ______12 electrons # n ______ Lewis Dot: Lewis Dot: # e ______10 # e ______ 2+ Electronic 1s2 2s2 2p6 3s0 [Mg] Electronic Configuration: Configuration: Supplemental packet page 50 Ionic Structure Atomic Number: 11 Physical Properties: Atomic Number: 17 • • Physical Properties: sodium-23 ion chloride-35 ion nonmetal anion Name: • • metal cation Name: • • 23 1+ • positive ion 35 1- • negative ion Symbol: Na • • • Symbol: Cl • • • • 11 • • 1+ charge 17 • • • • 1- charge • Chemical • • Chemical mass # 23 • • Properties: mass # 35 • • Properties: combines w/ • • combines w/ # p ______11 More protons than # p ______17 anions cations # n ______12 electrons # n ______18 10 Lewis Dot: 18 Lewis Dot: # e ______ # e ______ More electrons than • • Electronic 1+ Electronic protons [Na] [• Cl •]1- Configuration: 1s2 2s2 2p6 3s0 Configuration: 1s2 2s2 2p6 3s2 3p6 • • Atomic Number: 12 Physical Properties: Atomic Number: 8 Physical Properties: magnesium-24 ion metal cation nonmetal anion Name: • • Name:oxygen-16 ion • • 24 2+ • positive ion 16 2- • negative ion Symbol: Mg • • • Symbol: • • • 12 • • 2+ charge 8 O • • 2- charge • Chemical • Chemical mass # 24 • • Properties: mass # 16 • • Properties: combines w/ combines w/ # p ______12 More protons than # p ______ 8 anions cations # n ______12 electrons # n ______ 8 Lewis Dot: Lewis Dot: # e ______10 # e ______10 More electrons than protons • • Electronic 2+ Electronic • • 2- 1s2 2s2 2p6 3s2 [Mg] 1s2 2s2 2p6 3s0[• O •] Configuration: Configuration: • • 5 Supplemental packet page 60 Atomic Radii Ionic Radii Very closely linked to the atomic radius is the radius of ions formed from the atoms. Cations: In a qualitative sense, if an electron is removed there are fewer electrons for the same nuclear charge, Zeff, to attract. As a result when a neutral atom loses an electron the remaining electrons are more strongly attracted and are pulled closer to the nucleus. As a result the radii of positive ions are smaller than the corresponding atom. The more electrons that are removed in forming ions the smaller the radius becomes. Anions: The reverse occurs when a negative ion is formed by gaining an electron. The electron added is in the same energy level as the other valence electrons but the effective nuclear charge, Zeff, is lower in comparison to the number of valence electrons. The attraction of the nucleus for each electron is less than before and the negative ion has a larger radius than the neutral atom. Forming -2 and -3 ions increases the size of the ion even more. Compare the atomic and ionic radii for these selected atoms. Ionic Radius Variation in the Periodic Table - Relative Size Trends cations < anions 3+ 2+ + - 2- 3- multiple charge Al < Mg < Na < < F < O < N Same Row Elements Multiple Charge + + + 2- 2- 2- family trend Li < Na < K < <O < S < Se Elements of the same family Cations Anions Anions are larger than cations Familiarize yourself with these ion trends 6 Plasmas (hot gaseous ions) - The Fourth State of Matter ions negative positive – Reduction 1X + 1 1X + - - 1M 1M + 1 Oxidation (RIG) e gain e loss (OIL) Å anion anions are larger than cations cation - + X > M HOT gaseous ions (making plasmas) Electron Affinity (EA) Ionization Energy (IE) + energy energy Å 1X(g) + 1 1X (g) released absorbed + 1X(g) 1X (g) + 1 Ionization Energy Ionization Energy (IE) energy + absorbed + 1X(g) 1X (g) + 1 Ionization energy is the energy required (absorbed) to remove an electron from an atom in the gaseous state •IE energies are always postive in numerical value •the smaller the IE, the more easily an electron can be removed •IE is a measure of how strongly the electrons are held by the nucleus •direction of increasing IE •He has •francium has the lowest IE the highest IE Å Cl endothermic + Å Li Li Cl O energy exothermic - energy Å absorbed + 1X(g) 1X (g) + 1 endothermic 7 Ionization Energy Ionization energy is how much energy it takes to pull an electron away from each atom in the gaseous phase, Ionization Energy (IE) energy + absorbed + 1X(g) 1X (g) + 1 If we plot