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CHAP 2 Atoms, Molecules, and ions History • Greeks • everything made up of 4 fundamental substances (earth,air,fire,water) • “atomos” – later became atom – small, indivisible particles • Dalton’s Atomic Theory – • Each element made up of atoms • Atoms of same element same; different element different • Compounds form from combinations of elements in definite proportions. • Chemical reactions involve rearrangements of atoms. More History • Thomson – studied cathode-ray tubes/Plum Pudding Model • Negative particle (electron) • Determined charge to mass ratio of electron • Milikan – Oil Drop Experiment • Determined magnitude of electron charge • Rutherford – Gold Foil Experiment • Found positive center of atom (nucleus) • Positive particle – proton • Bohr – model of Hydrogen atom • Chadwick – discovered neutron Key Terms Atomic mass – average # of protons & neutrons in an atom Atomic weight – weighted average mass determined by a standard Atomic number – # of protons in an atom Mass number – total # of protons & neutrons Isotope – same # protons, but different # neutrons Ion – gain or lost electrons (no longer equal to # protons) Neutral atom – equal # of protons and electrons Nucleus – positively charged, dense center of the atom Atomic Structure Symbol Mass Charge Location Proton P+ 1 + nucleus Neutron n0 1 - nucleus Electron e- 0 0 Electron cloud Nucleus – contains mass of atom Electron cloud – gives volume to atom Periodic Table • Types of elements • Metals – left side; majority of elements; good conductors; lose electrons (+ ions) • Nonmetals – right side; poor conductors; gain electrons (- ions) • Metalloids – stair-step line • Groups – columns; grouped by similar properties • 18 – each has a name • Periods – rows •7 More on Periodic Table • Group 1 – Alkali Metals • Group 2 - Alkaline Earth metals • Groups 3-12 – transition metals • Groups 13-16 – named after first element and word family (ie. Carbon family – group 14) • Group 17 – Halogens • Group 18 – Noble Gases • Bottom – Lanthanide and Actinide series Naming Binary Compounds • Cation (+ion) named first, anion (-ion) named second • First element is named as the element • Second element, keep root & change ending to – ide • if has more than 1 charge possible, use Roman numeral to indicate charge of metal (systematic) • May use latin root of element – higher charge ends in –ic, lower charge in –ous • Polyation ions named as is – change nothing • If covalent compound (2 nonmetals) – need to use prefixes. Formula Writing • Compound needs to be electrically neutral – balance out charges. • Criss-cross the ion charges to become the subscripts in the formula. • Polyatomic ions belong in parentheses. Any crisscrossed subscript goes outside parentheses. • Remember roman numeral indicates charge of that metal. • Prefix value goes with the element it is attached to – no criss-crossing if have prefix. Acids • Always contain hydrogen first in the formula • If it does not contain oxygen (just H and another element), named with prefix hydro-, root, and ends in –ic. • If does contain oxygen, if polyatomic ion ends in –ite, acid ends in –ous. If polyatomic ion ends in –ate, acid ends in -ic