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Lecture 4

CHEM 1A03 LECTURE 4 SEPTEMBER 25-30 - THE PERIODIC TABLE AND SOME ATOMIC PROPERTIES.docx

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Department
Chemistry
Course
CHEM 1AA3
Professor
David Brock
Semester
Spring

Description
CHEM 1A03 LECTURE 4 - THE PERIODIC TABLEAND SOMEATOMIC PROPERTIES th September 25 2012 **READ AHEAD for next lecture. Noble Gases, Group 18A • ns np electron configuration • Considered chemically “inert” until 1962. Many noble gases form known compounds. Non-metals • Main group (s and p block) – tend to gain electrons. • Ability to oxidize increases towards the upper period. o For instance, Cl2can rip electrons from I-, yet B2 cannot rip from Cl-. • React with metals to form salts. (SEARCH: synthesis of NaCl) • Halogenic Melting/Boiling point increase down group 17A. Metals • Main group (s and p block) metals (and H) tend to lose electrons. • Alkali metals (group 1) oxidize more readily than alkaline earth metals. • Both oxidize easy in water – KNOW: how to write their reactions. General Trends in physical properties • Across a period: o Metallic properties decrease. o Melting point varies with type of bonding (network covalent>metallic>ionic>molecular) o Atomic radius decreases (Z increases, but e- are added to the same n valence shell with same number of core electrons. These valence e- feel stronger attraction to nucleus (higher Zeff) • Down a group: o Principle quantum number (n) increases, thereby increasing atomic radius • As r (atomic radius) increases (electrons are placed in further shells, n increases) electric field decreases and valence electrons… Key idea for periodic trends • How are the electrons held? • Electrostatic interactions of the nucleus (+) and electrons (-) 2 • E = kQ nucleus Screening • Outer e- of an atom are screened by the core e- from feeling the full attractive charge (Z) from the nucleus. • Outer e- feel an effective nuclear charge, Zeff. • Simply, ZeffZ – S, where S = #core e-. • In reality, s,p, and d e- are screened differently. Ionic radius • Metals and metalloids have ionic radius SMALLER cations than their corresponding element. • Non-metals have an ionic radius much LARGER anion than their corresponding element. • Isoelectron ions/atoms: size decreases as Z increases. F- > Ne > Na+ (THINK: what happened in the nucleus?) CHEM 1A03 CHAPTER 10 – CHEMICAL BONDING • Involves transfer or sharing of outer electrons usually to aquire a
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