Chemistry Exam Notes Unit 1 & 2 - Matter and Chemical Reactions Atomic Theory: History: - Democritus: Matter is made up of indivisible particles called “atomos” - Dalton: Atoms are small spheres, each element had different masses (bowling ball model) - Thomson: Atoms are positively charged clouds with negatively charged electrons spread around it (plum pudding model) - Rutherford: After shooting alpha particles at gold foil, Rutherford discovered that every atom has a positively charged nucleus - Bohr/Nagaoka: Bohr suggested that electrons orbit the nucleus in fixed energy levels (electron shells). Nagaoka suggested a Saturnian model near the same time - Chadwick: Discovered the neutron - Modern Theory: We can only predict the location of an electron in shapes of probability called orbitals (electron cloud theory) Protons: Relative mass = 1, Charge 1+, Symbol: p+ Neutrons: Relative mass = 1, Charge 0, Symbol n0 Electrons: Relative mass = 1/1836, Charge 1-, Symbol e- Atomic Number (Z): Equal to the number of protons Mass Number (A): Equal to #p+ + #n0 Ion: Charged atom Modern Atomic Theory: Bohr-Rutherford Diagrams: Octet Rule: The tendency for atoms to have 8 electrons in the valence shell Cation: a positively charged ion, made by losing e- (Mg (2e- in valence) → Mg2+ (8e- in valence))
Anion: a negatively charged ion, made by gaining e- (Cl (7e- in valence) → Cl- (8e- in valence)) Isotopes: elements with different numbers of neutrons in their nuclei, have the same chemical properties but different physical properties Average Atomic Mass and Isotopic Abundance: Ex. 75% Cl-35, 25% Cl-37, 0.75(35) + 0.25(37) = Avg Mass, 35.5 = Avg. Mass Periodic Table: - Created by Mendeleev - Table divided into groups (columns), and periods (rows) - Every element in the same group has the same number of valence e- - Every element in the same period has the same number of e- shells - Atomic Radius: Radius of atom, increases down (more shells) and left (less positive charge attracting shells) on periodic table - Ionization Energy: Energy required to remove an electron from a neutral atom, increases up and right (since the smaller the atomic radius, the more energy is required to remove an e-) - Reactivity: Likelihood of an element reacting with another substance, increases down and left - Electronegativity: An atom's ability to attract and bind with electrons, increases up and right - Electron Affinity: T he ability of an atom to accept an electron, increases up and right (since atoms with less e- want to lose them more to earn stable octet) - Ionic Radius: Radius of an ion, more e- = bigger radius, less e- = smaller radius Nomenclature: Ionic: - 2nd element ends in -ide - Multiple charges (indicate with parentheses and roman numerals) - Polyatomic Ions Covalent: - Prefixes - No “mono” on 1st atom Acids: - Binary Acids: no polyatomic ions, write “hydro-...-ic acid” (ex. hydrochloric acid) - Oxy Acids: polyatomic ions, write “-ic/ous acid” (ex. nitrous acid) Atomic Bonding: Ionic Bonds: - Transfer of electrons - Involves a metal and non-metal - Difference in electronegativity > 1.7
- Lewis Dot Diagram: Covalent Bonds: - Sharing of e- - Involves 2 non-metals -
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