Chapter 3: Intro To the Periodic Table

Chapter 3: Intro To the Periodic Table

History • 1800’s- 60 known elements + their atomic masses • 1829 - Döbereiner’s Triads (groups of 3) • Some elements grouped in 3’s by their properties • Physical properties of the middle element usual about ½ way between those of the other 2 elements. • Ex: Halogen Triad: Cl, Br, I (see Table 3.1, p 87)

Döbereiner Triads • Halogen Triad: Cl, Br, I • Alkali Triad: • Li = 7 g • Na = ? • K = 39 g • Coinage Metals Triad: Cu , Au, Ag

History (cont.) • 1869- Dmitri Mendeleev noticed that properties of elements repeated in an orderly way when organized by atomic mass. This is periodicity. • He put them in order from lightest to heaviest (atomic mass) & grouped them when properties repeated themselves. (see Table 3.3 on p 90 of text)

History, cont. • Even though Mendeleev couldn’t identify Zn, Si, and Ca, he was able to predict • their existence and • their behavior!

Modern Periodic Table • Elements placed in order of increasing atomic number. • Noble gases have been added • Synthetic elements too • Each period begins w/ a metal & ends w/ a noble gas (see p 92- 93)

Using the Periodic Table (Review) • Groups • Group # for Main Group Elements indicates the # of v.e-s • Elements in a group have similar chemical properties b/c the # of v.e-s is the same (AND VALENCE ELECTRONS DETERMINE CHEMICAL REACTIVITY!) • Periods • Period # indicates the energy level of the v.e.-s

Using the Periodic Table, cont. (New Info) • Periods • Each period ends with a Noble Gas • Each period ends with • a full s sublevel (___ v.e.-s) OR • full s & p sublevels (___ v.e.-s)

Using the Periodic Table, cont. • Group Names • Group #1: Alkali Metals • Group #2: Alkaline Earth Metals • (Group #16: Chalcogens) • Group #17: Halogens • Group #18: Noble Gases

Physical States of the Elements • The P. Table shows the state of the elements at room temperature. • Most elements are solid • Some elements are gas (most on right side of P Table. Only H is on left.) • 2 elements are liquid (Br & Hg)

3 Classes of the Elements: Common Properties

Metalloids • Metalloids are often called semiconductors. • They conduct heat & electricity, but poorly • This is good in computers b/c they don’t overheat. • Doping is used to make them better conductors.

Metalloids & Doping • Have an electron arrangement that keeps them from moving freely. • Ex: each germanium atom (Ge) has 4 v.e.-s it shares with 4 neighboring Ge atoms. • This creates a stable lattice, in which e-s are spaced evenly throughout the Ge, so they don’t move

Metalloids & Doping • “Doping”- If you place an occasional atom of another element, In or As, among the Ge atoms, you increase the movement of the e-s

2 Types of Doping n-type: creates a shortage of e-s, in some areas, so they move to try to even out the charges Indium has 3 v.e.-s, so in the lattice, there are “holes”- areas missing an e-

2 Types of Doping p type: creates an excess of e-s in some areas, so they move to try to even out charges

Chapter 3: Intro To the Periodic Table