CHAPTER 6: Periodic Table

Development of Periodic Table Mendeleev Contributions – made very first periodic table p.t. arrangement: elements ordered by increasing atomic mass

Development of Periodic Table 3) Noticed periodic pattern (repetition) in element properties - elements placed in groups w/ similar properties - Left gaps for substances yet to be discovered

Mendeleev’s Periodic Table (1871)

4) errors: when new elements discovered, several elements on his table didn’t fit right - had different properties

Moseley periodic table arrangement: elements ordered by increasing atomic number Periodic Law – when elements arranged by increasing atomic number, their physical & chemical properties show a periodic pattern

Modern Periodic Table Boxes contain: Element name Element symbol Atomic number Atomic mass

Modern Periodic Table Arrangement – increasing atomic number a) groups – columns (vertical) b) periods – rows (horizontal)

Two Divisions of Elements Main Group Elements – groups 1A, 2A and 13-18A (s & p block)

Two Division Of Elements Transition Elements – group 3-12B elements (d block)

Classifying Elements Metals – elements w/ shine – solid @ room temp – conducts heat & electricity – malleable: put into thin wires – ductile: pound into sheets

Metals a) Alkali Metals – group 1A (except H) - highly reactive, very soft b) Alkaline Earth Metals – group 2A - less reactive and denser than alkali metals c) Transition Metals – d-block (group 3-12B)

Metals La Ac d) Inner transition metals – f-block i) Lanthanide Series – row 1 of f-block ii) Actinide Series – row 2 of f-block La Ac

Nonmetals Defn - gases or brittle, dull looking solids - poor conductors of heat & electricity a) Halogens b) Noble Gases - group 17A - highly reactive - group 18A - very unreactive/stable

Metalloids Defn – BORDER THE STAIRSTEP LINE  - Have similar chem & phys props as both metals and nonmetals

Alkali metals Alkaline earth metals Halogens Noble Gases Transition Metals Lanthanides Actinides

Organizing Elements By Electron Configuration Valence Electron – electrons in highest energy level atoms in same group have similar chemical props b/c they have same # of valence e-

Valence Electrons And Period The period indicates what energy level the valence electrons are located on Ex: [Ar] 4s2 3d10 4p1 3 Valence e- on 4th energy level

Valence Electrons and Group Number # of valence electrons equals group number (only for main group elements) exception: Helium (in group 18, but has 2 valence e- only)

Ex Problems [Ne] 3s2 [He] 2s2 2p4 [Kr] 5s2 4d105p5 2 16 17 3 2 5 s p p Tell the group, period, and block where these elements are located [Ne] 3s2 [He] 2s2 2p4 [Kr] 5s2 4d105p5 2 group – period – block – group – period – block – 16 group – period – block – 17 3 2 5 s p p

Periodic Trends There are certain patterns that occur with the elements as you go across and down the periodic table which atom is the biggest? smallest? which atom is most reactive/least stable?

Atomic Radius (size) Defn – distance from center to edge of electron cloud Period Trend – decreases from left to right Why? increasing # of protons (+ charge) in nucleus has a greater attraction for electrons (- charge)

Atomic Radius Group Trend – increases from top to bottom Why? electrons occupy higher energy levels and are farther from the nucleus Period 1 Period 2 Period 3

Atomic Radius Summary decreases increases

Ion Defn – atom w/ a positive or negative charge - atom lost or gained electrons - # protons ≠ # electrons

Cation Defn – positive ion (atom lost e-) - more protons than electrons Comparing atom size vs. its cation size A A+ atom A cation of atom A cations are SMALLER than its original atom

Anion Defn – negative ion (atom gained e-) - more electrons than protons Comparing atom size vs. its anion size A- A atom A anion of atom A anions are LARGER than its original atom

Ion Summary A- A A+ < < cation atom anion

Ionization Energy Defn – energy required to remove an electron from an atom Period trend – IE increases from left to right Why? increased nucleus charge has greater hold on valence e-

Ionization Energy Group Trend – IE decreases from top to bottom Why? atomic size increases, valence e- are farther away so easier to remove (less energy required)

Period 1 Period 2 Period 3

Ionization Energy Summary increases decreases

Ex problem Cl > Ba > Cs Rank these atoms from increasing to decreasing ionization energy: Ba, Cs, Cl increases decreases Cl Cs Ba Cl > Ba > Cs

Electronegativity Defn – relative ability of an atom to attract electrons in a chemical bond “how badly does atom want electrons” while in a bond Period Trend – increases from left to right Group Trend – decreases from top to bottom

Electronegativity Summary increases decreases

Ex problem O > Mg > Sr Rank these atoms from high to low electronegativity: O, Sr, Mg increases decreases Mg O Sr O > Mg > Sr