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Chapter 2 Atoms, Molecules, and Ions Matter • What accounts for matters secrets? – Atomists – Democritus – All things are made of Fire – Herclitus – Four Elements – Aristotle Conservation of Mass and Law of Definite Proportions • Robert Boyle (1627–1691): Provided evidence for the atomic nature of matter. – Element - A substance that cannot be chemically broken down further • Joseph Priestley (1733– 1804): Conservation of Mass and Law of Definite Proportions • Antoine Lavoisier (1743-1794): Conservation of Mass • Law of Mass Conservation: Mass is neither created nor destroyed in chemical reactions. Hg(NO3)2 + 2 KI → HgI2 + 2KNO3 3.25g + 3.32g → 4.55g + 2.02g 6.57g = 6.57g Law of Definite Proportions • Law of Definite Proportions: In a unique compound the elements will always be found in the exact same ratio. Dalton’s Atomic Theory and the Law of Multiple Proportions • John Dalton (1766–1844): Proposed explanations for the laws of mass conservation and definite proportions. – Postulate 1: Elements are made of atoms – Postulate 2: Atoms of the same element have the same properties (including mass). Atoms of different atoms have different properties – Postulate 3: Compound are comprise of elements joined together in small whole ratios – Postulate 4: Chemical reactions only rearrange the way the atoms are combined Dalton’s Atomic Theory and the Law of Multiple Proportions • Law of Multiple Proportions: – When two elements form two different compounds, the mass ratios are related by small whole numbers. The Structure of Atoms: Electrons • Elements are composed of atoms • Compounds are composed of atoms of elements in a given ratio • What does an atom look like? The Structure of Atoms • Structure of the Atom: The Structure of Atoms • Comparison of Subatomic particles Particle Grams amu Coulombs e Electron 9.109382 x 10-28 0.0005485799 -1.602176 x 10-19 -1 Proton 1.672622 x 10-24 1.007276 1.602176 x 10-19 1 Neutron 1.674927 x 10-24 1.008665 0 0 Atomic Number • # protons in an atom determines the element – atomic number (Z) - Atomic number is found on the periodic table • # electrons = # protons in a neutral atom Mass Number • mass of the atom ≈ # neutrons + # protons – Mass number = # protons + # neutrons – An element may have more than one mass # • Hydrogen, Deuterium, Tritium • Isotopes: Atoms with identical atomic numbers, but different mass numbers. • Due to different # of neutrons NOT protons Atomic Mass • Atomic Mass: A weighted average of the isotopic masses of an element’s naturally occurring isotopes. – Unit – atomic mass unit (amu) Example • Chlorine has two naturally occurring isotopes: with an abundance of 75.77% and an isotopic mass of 34.969 amu, and with an abundance of 24.23% and an isotopic mass of 36.966 amu. What is the atomic mass of chlorine? Compounds and Mixtures Chemical Bonds • 2-types of bonding are found in compounds – Ionic bond – Covalent bond Ionic Bond Molecules, Ions and Chemical Bonds • Ionic Bonding (Ionic Solids): Occur between metal and non-metal Ionic Bonds Problem • Which of the following ions occurs commonly? – A. – B. – C. – D. – E. N3+ S6+ O2Ca+ Cl+ Ionic Bonds Ionic Bonds • Formula for Ionic Compounds – Ions combine to form neutral compounds Examples: Na+ and Cl– combine to form NaCl. Ca2+ and Cl– combine to form CaCl2. Al3+ and Cl– combine to form AlCl3. Fe2+ and Cl- combine to form FeCl2. Molecules, Ions, and Chemical Bonds Naming Chemical Compounds • Naming Ionic Compounds - name the cation, then name the anion. – The positive ion (the metal or ammonium) • Single charge or ammonium – write its name • More than one possible charge – Write the elements name – Indicate the magnitude of charge as a roman numeral in parenthesis – The negative ion (non-metal or polyatomic ion) • Non-metal element - write root of element name with suffix –ide • Polyatomic – write the ions name Problem • Which one of the following combinations of names and formulas of ions is incorrect? – A. – B. – C. – D. – E. O2- oxide Al3+ aluminum NO3- nitrate PO43- phosphate CrO42- chromate Problem • Which one of the following combinations of names and formulas of ions is incorrect? – A. – B. – C. – D. – E. Ba2+ barium S2- sulfate CN- cyanide ClO4- perchlorate HCO3- bicarbonate Problem • Convert the names into formulas and the formulas into names – Sodium oxide – BaO – CoCl2 – (NH4)2S – Zinc Acetate – Chromium (VI) oxide Covalent Bond Molecules, Ions and Chemical Bonds • Covalent Bonding (Molecules): Between 2 non-metals or a non-metal and a metalloid. Covalent Bonds Naming Chemical Compounds • Naming Binary Molecular Compounds: – Identify which element is more cationlike. Naming Chemical Compounds • If cation-like element is H and anion-like element is O, S, Se, or a halogen – Name hydrogen – Name the anion-like element using root and – ide ending Naming Chemical Compounds • All other non-metal / metalloid combinations – Name the cation-like element – Name the anion-like element with root and –ide – Using prefixes indicate how many of each atom is present Covalent Compounds • Formula – Translate name of each element – Make the prefix of the element it’s subscript Problem • Convert formulas into names and names into formulas – PCl3 – Diiodine pentoxide Naming Compounds • Acids – are a special type of covalent compound – Acids are species that dissociate to form H+ cations and an anion when added to water. • Hence you will need to be told that they are aqueous compounds (aq) – Acids are typically indicated by writing the H first in the formula • Elemental symbols are typically written in alphabetical order Naming Compounds • Acids cont. – For current purposes, acids are going to be described as aqueous compounds of H combined with a group 17 element or a polyatomic ion. – H with group 17 elements or cyanide • Named as hydro + 17 element root + ic – H with all other polyatomic ions • Root of polyatomic ions ending in -ate + ic • Root of polyatomic ions ending in –ite + ous Problem • What is the name of the acid formed when HBr gas is dissolved in water? – A. – B. – C. – D. – E. bromic acid bromous acid hydrobromic acid hydrobromous acid hydrobromidic acid Optional Homework • Text – 2.26, 2.28, 2.29, 2.38, 2.46, 2.48, 2.50, 2.52, 2.54, 2.56, 2.58, 2.68, 2.78, 2.82, 2.84, 2.86, 2.88, 2.90, 2.96, 2.100, 2.104, 2.112 • Chapter 2 Homework – from website