Development of the Periodic Table Mendeleev developed periodic table to group elements in terms of chemical properties. Alkali metals develop +1 charge, alkaline earth metals + 2 Nonmetals usually develop negative charge (1 for halides, 2 for group 6A, etc.) Blank spots where elements should be were observed. Discovery of elements with correct properties. John A. Schreifels Chemistry 211

Periodic Properties Periodic law = elements arranged by atomic number gives physical and chemical properties varying periodically. We will study the following periodic trends: Atomic radii Ionization energy Electron affinity John A. Schreifels Chemistry 211

Periodic Trends OBJECTIVES: Interpret group trends in atomic radii, ionic radii, ionization energies, m.p., b.p., electronegativity and chemical properties

Trends in Atomic Size First problem: Where do you start measuring from? The electron cloud doesn’t have a definite edge. They get around this by measuring more than 1 atom at a time.

Atomic Size } Radius Atomic Radius = half the distance between two nuclei of a diatomic molecule.

Trends in Atomic Size Influenced by three factors: 1. Energy Level Higher energy level is further away. 2. Charge on nucleus More charge pulls electrons in closer. 3. Shielding effect e <-> e repulsion

Shielding The electron in the outermost energy level experiences more inter-electron repulsion (shielding). Second electron has same shielding, if it is in the same period

Periodic Trend Metals are at the left of the table. They let their electrons go easily At the right end are the nonmetals. They want more electrons. Try to take them away from others

Periodicity and chemical properties Most obvious trend is from metallic to non-metallic Acid-base properties of oxides: Metal oxides tend to be basic (Na2O = NaOH in H2O) Nonmetal oxides tend to be acidic (SO2 = H2SO3 in H2O)

Periodic Table/Periodicity Who? Newlands, Mendeleev, Moseley Layout Main, Transition, Lanthanides, Actinides Metals, Non-metals, Metalloids Properties Groups (Families), Periods Periodic Law Trends – Atomic Radii, Valence Electrons

Periodic Table: Arrangement Layout of the Periodic Table: Metals vs. nonmetals Nonmetals Metals

Across the Periodic Table Periods: Are arranged horizontally across the periodic table (rows 1-7) These elements are in the same energy level 2nd Period 6th Period

Down the Periodic Table Family: Are arranged vertically down the periodic table (group 1- 18 or 1-8 A,B) These elements have the same number electrons in the outer most shells, the valence shell. Alkali Family: 1 e- in the valence shell Halogen Family: 7 e- in the valence shell

Group trends As we go down a group... H As we go down a group... each atom has another energy level, so the atoms get bigger. Li Na K Rb

Periodic Trends As you go across a period, the radius gets smaller. Electrons are in same energy level. More nuclear charge. Outermost electrons are closer. Na Mg Al Si P S Cl Ar

Rb K Overall Na Li Atomic Radius (nm) Kr Ar Ne H 10 Atomic Number

Summary Periodic Table: Map of the Building block of matter Type: Metal, metalloid and Nonmetal Groupings: Representative or main, transition and Lanthanide/Actanides Family: Elements in the same column have similar chemical property because of similar valence electrons Alkali, Alkaline, chalcogens, halogens, noble gases Period: Elements in the same row have valence electrons in the same shell.