Honors Chemistry Chapter 6 the Periodic Table Organizing

Honors Chemistry Chapter 6: the Periodic Table

Organizing the elements • Dobereiner: triads: groups of three with similar characteristics; worked for a while, but this was before we discovered a lot of other elements • Mendeleev: table of elements, precursor to the modern PT • Another fellow, Meyer, had similar effort, but Mendeleev published first and had better explanations of usefulness • Arranged by atomic mass; today, we realize that we use atomic #, as there are several mass anomalies in the table (Co/Ni, Te/I, Bi/Po, Hs/Mt, Th/Pa, U/Np, Pu/Am, Lr/Rf, et al)

Organizing the elements • Periodic law: term for the repeating pattern (periodicity) of the elements; this refers to the repetition of characteristics (think “valence electron behavior”) of the elements in each column/group/family • Classes of elements • Metals: low # of v. e. , good conductors of heat/electricity due to the mobility of these v. e. , malleable, ductile • Nonmetals: higher # of v. e. , many are gases at room temp. , opposite char. Of metals: nonconductive, any solids are brittle • Metalloids/semimetals: properties of both, particularly dealing with electric current flow; follow stair steps between B and Al

Classifying elements • Groups/families • 1/Ia: alkali metals: extremely reactive, soft metals, never found unbonded in nature • 2/IIa: alkaline earth metals: quite reactive, also usually found only in cpds. • 17/VIIa: halogens: extremely reactive nonmetals, never found unbonded in nature • 18/VIIIa: noble gases: extremely unreactive nonmetals • Representative groups • • 13/IIIa: boron group: metalloids, metals 14/IVa: carbon group: nonmetal, metalloids, metals 15/Va: nitrogen group: nonmetals, metalloids, poor metal (Bi) 16/Via: oxygen group: nonmetals, metalloid (Te), metal (Po)

Classifying elements, continued • Transition metals (outer): d block metals • More commonly found metals • May have multiple oxidation states • (oxidation state: number which represents how many electrons are gained or lost; example: iron can be either Fe 2+ or Fe 3+) • Transition metals (inner): f block metals • Lanthanide series: also called rare earth elements, for general scarcity • Actinide series: mostly synthetics above Uranium, can be called transuranics

Periodic trends • These are patterns of behavior in the elements, a large part of the utility of the periodic table: you will have much of this in some handouts we have done in class (“Periodic Table Activity, ” “Periodicity worksheet”) • Atomic size: repeats row to row, getting smaller left to right, larger as go down table (higher number) • Ion size: same pattern

Periodic trends, continued • Trends in ionization energy: this is a bit of a thinking exercise • It depends upon how many valence electrons are available to be lost • The first energy BEYOND the normal number of v. e. is MUCH HIGHER, as this is coming from the next lower energy level • As you move left to right across a row, the first ionization energy increases incrementally (a modest amount), with the highest being the noble gas at the far right • These energies decrease a bit as you to higher energy levels, meaning Na is less than Li, K less than Na, etc

Periodic trends, continued, again • Electronegativity: a relative measure of how much an element wants to attract an electron from some other element • Increases from lower left to upper right; Fluorine is highest/most electronegative (will take one from about anything else, and not let go), Cesium lowest/least electronegative (really wants to get rid of electron) (we think Francium would exceed this, but since we just about never have any around…remember the hypothesized reaction in the video about alkali metal reactivity…yeah!)