Unit 4: Periodic Table Overview- Honors Chemistry Periodic Table Classifying Atoms Octet Rule Periodic Trends Metals: Increasing stability /lowering Reactivity, valence electrons, Alkali, alkaline earth, energy (Coulomb's law) core charge, atomic radii, transition, inner transition valence electrons, cations, ionic radii, ionization energy, (rare earth- lanthanides and anions electronegativity actinides) Non-metals: Halogens, noble gases Metalloids Enduring Understandings I. Chemists use the properties of elements to sort them into groups. Mendeleev arranged the elements in his periodic table in order of increasing atomic mass. Science has predictive power. Mendeleev was able to use his table to predict the properties of undiscovered elements. Moseley studied atoms with x-rays and arranged his periodic table in order of increasing atomic number. For the first time, regions of the periodic table were “filled.” II. Valence electrons- electrons in the highest occupied energy level (n) For any representative element- use group number to determine the number of valence electrons. Valence electrons and valence shell electron configuration influence physical and chemical properties considerably III. Shielding- valence electrons experience less nuclear attraction due to two contributing factors: Distance from the nucleus (valence electrons are further from the nucleus) Electron repulsion (valence electrons are repelled outward by electrons in the core of the atom) IV. Octet rule- in forming compounds, atoms tend to seek the lower energy / greater stability by achieving the electron configuration of the nearest noble gas. Metals lose electrons while forming octets Non-metals gain electrons while forming octets V. Ions- atoms or group of atoms with a charge Cations are positively charged ions that are often formed from group IA-IIIA metals. Anions are negatively charged ions that are often formed from group VA-VIIA non-metals. VI. Ionization energy- energy required to remove an outermost electron VII. Electronegativity- ability of an element to attract electrons toward itself when bonding in a compound Pauling scale- relative indication of electronegativity; based on fluorine (F) as highest- 4.0 VIII. Physical and chemical properties are a function of atomic number. Reactivity Atomic / ionic radius Decreasing across series- valence electrons and core charge increasing Increasing down group- shielding Ionization energy Increasing across series- moving toward non-metals with smaller radius that are seeking octet by gaining electrons Decreasing down group- shielding (easier to remove a valence electron when more shells are present) Electronegativity Increasing across series- moving toward non-metals with smaller radius that are seeking octet by gaining electrons Decreasing down group- shielding (harder to attract electrons with more shells present) .