CHEM 1A03 LECTURE 4 - THE PERIODIC TABLEAND SOMEATOMIC
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.
• 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.
• 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 (-)
• E = kQ nucleus
• 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.
• Metals and metalloids have ionic radius SMALLER cations than their corresponding
• Non-metals have an ionic radius much LARGER anion than their corresponding
• 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