Periodicity. Sizes of Atoms. Atomic radii increase with increasing electron shielding. Atomic radii decrease with increasing effective nuclear charge.

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1 Periodicity! Sizes of atoms and ions! Ionization Energy! Electron affinity! Electronegativity! Metallic Character! Diagonal Relationships! Multiple Bonding 1 Sizes of Atoms Atomic radii increase with increasing electron shielding. Atomic radii decrease with increasing effective nuclear charge. Periodicity 2 2

2 Ion Size!Cations have radii than their neutral atoms.!anions have radii than their neutral atoms. 3 Sizes of atoms and ions Even though cations have smaller radii and anions have larger radii than neutral atoms, the periodic trends in size are still valid for both atoms and ions. 4

3 IONIZATION ENERGY Definition of Ionization energy (IE): Na(g)! Na + (g) + e - Ionization energy always Energy (endo or exo?) What are the trends?!!moving down a group, IE because of increased electron shielding.!!moving across a row from left to right, IE because of increased effective nuclear charge. 5 Is it easier to remove an electron from a 2p orbital or one from a filled 2s orbital? Ionization energy Is it easier to remove an electron if it is un-paired or paired? 6

4 ELECTRON AFFINITY Electron affinity: opposite of Electron affinity is the energy change when a gaseous atom an electron to form a gaseous ion: Cl(g) + e -! Cl - (g) Electron affinity can either be exothermic (as the above example) or endothermic: Mg(g) + e -! Mg - (g) Electron affinity generally in magnitude toward the top and the right on the periodic table. 7 Due to decreasing atomic radius, electronegativity moving up a group on the periodic table. Definition of Electronegativity: Due to increasing nuclear charge, electronegativity moving across a period from left to right. 8

5 OXIDATION STATES Atoms tend to lose or gain electrons to achieve what kind of configuration? Elements to the right of the periodic table are electronegative gain electrons to become negatively charged anions or oxyanions. Elements to the left of the periodic table are electropositive lose electrons to become positively charged cations. NaCl! MgO! For main group elements: The highest possible positive oxidation state is equal to what? 9 Acid Strength and Electronegativity Recall trends in oxyacid strength that are related to electronegativity: HClO 4 HBrO 4 HIO 4 (What is the reason for this?) 10

6 Metallic Character refers to the Properties of Metals: a) shiny or lustrous b) malleable and ductile c) oxides form basic ionic solids d) tend to form cations in aqueous solution Metallic character: down a group. across a period. Metallic Character Metals have low ionization energies. Most neutral metals prefer to be oxidized (become more positive) rather than reduced. 11 Demonstrate Acid/Base Character of Oxides & Hydroxides Oxide + H 2 O! Hydroxide Element Oxide Hydroxide Acidic or Basic Na Na 2 O NaOH Mg (Ca) MgO Mg(OH) 2 Al Al 2 O 3 Al(OH) 3 Si SiO 2 Si(OH) 4 P P 2 O 5 PO(OH) 3 S SO 3 SO 2 (OH) 2 Cl Cl 2 O 7 ClO 3 (OH) 12

7 Amphoterism: ability of a molecule to act both as an acid and a base. This results in metal hydroxides which are soluble in both acids and bases. Al(NO 3 ) 3 (s) + H 2 O! Al 3+ (aq) + 3NO 3z (aq) Hydration: Al 3+ (aq) " Al(H 2 O) 6 3+ Al(H 2 O) OH z Al(OH) 3 (H 2 O) 3 (s) In acid: Solubility increases! Al(OH) 3 (H 2 O) 3 (s) + H + Al(OH) 2 (H 2 O) 4 + (aq) In base: Solubility increases! Al(OH) 3 (H 2 O) 3 (s) + OH z Al(OH) 4 (H 2 O) 2 z (aq) + H 2 O 13 METALS NONMETALS AND METALLOIDS Metals (75% of elements)!lustrous, shiny!(almost) all solids!malleable & ductile!good conductors of heat/electricity!oxides/hydroxides are Nonmetals!Non-lustrous, often colored!gases, liquids, & solids!solids are brittle!poor conductors of heat/electricity!oxides/hydroxides are!aqueous cations (n+)!aqueous anions (n-) or oxyanions!reactivity downwards in family!reactivity downwards in family 14

8 Active metals (Groups 1 and 2) All solids at STP Not found in nature as pure metals, always combined with other elements (e.g. salts in the ocean, minerals) Reactive with H 2 O, O 2, and H 2 (alkaline earth metals more stable than alkali metals higher ionization energies) Family Group I Alkali Metals Group II Alkaline Earths Electronic ns 1 Config Oxidation State +1 Melting Point Low Bonding Ionic Oxides and Basic Hydroxides ns 2 +2 Higher Ionic (except Be) Basic (except Be) amphoteric Electropositive Most Yes Very Reactive React with Air, Water Harder/Stronger 15 Periodic trends in oxidation states Driving force: atoms tend to lose or gain electrons to achieve an inert gas configuration Common Oxidation states For main group elements (s and p block) The highest possible positive oxidation state Added stability in ns 2 subshell as you go down a family: inert pair effect 16

9 Periodic Trends in Bonding Nonmetals: covalent bonding, Oxides and hydroxides = acidic Metals: metallic bonding Metal/nonmetals: ionic, Metal oxides and hydroxides = basic 17 #-Bonding in Period II vs. III 18

10 DIAGONAL RELATIONSHIPS In many compounds, Li + resembles Mg 2+ rather than Na +. Examples: Li 2 CO 3 and MgCO 3 are virtually insoluble in water, while Na 2 CO 3 is very soluble. Ionic Radii: Li Å Be Na + Mg 2+ Al 0.95Å 0.65Å Be compounds are covalent and the hydroxide is amphoteric Similar to Al (example of a diagonal relationship) 19