1. The atomic theory Dalton’s Atomic Theory (1808) 1. Elements are composed of extremely small particles called atoms. 2.All atoms of a given element are identical, The atoms of one element are different from the atoms of all other elements. 3.Compounds are formed from atoms of more than one element in a fixed ratio. 4.A chemical reaction involves only the separation, combination, or rearrangement of atoms. Chapter 2Atoms, Molecules and Ions Law of definite proportions Atoms of any element are alike, atoms of different elements are different. CO, carbon monoxide: C/O = 1:1CO 2, carbon dioxide: C/O = 1:2 The ratio of atoms of different elements in a compound is an integer. Law of multiple proportions Law of conservation of mass 2 X + YX2YX2Y Rutherford’s Model of the Atom atomic radius ~ 100 pm = 1 x 10 -10 m nuclear radius ~ 5 x 10 -3 pm = 5 x 10 -15 m Relative ChargeRelative MassLocation Proton1~ 1 amunucleus Neutron0~ 1 amunucleus Electron1/1840 amuoutside nucleus Mass and Charge Electron cloud outside nucleus

2. Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons number of protons = number of electrons X A Z Mass Number Atomic Number Element Symbol 2.2 Atomic number, Mass number and Isotopes Isotopes Isotopes: same element, different number of neutrons The Isotopes of Hydrogen H 1 1 H 2 1 H 3 1 Hydrogendeuteriumtritium How many protons, neutrons, and electrons are in C 14 6 ? 6 protons, 6 electrons, 14 – 6 = 8 neutrons, The periodic table: Column: groupRow: period 1A: alkali metal2A: alkaline earth metal7A: halogen8A: noble gas Different colors: metals, metalloids, nonmetals Molecules and ions -Molecular: involves shared electrons and consists of electrically neutral, discrete particles(molecules) H 2 O, O 2 -Ionic compounds: involves electron transfer and charged particles (ions) NaCl compounds are of two types:

3. Molecular Compound A polyatomic molecule contains more than two atoms: O 3, H 2 O, NH 3, CH 4 As a general rule, molecular compounds are formed when nonmetallic elements combine PeriodIVAVAVIAVIIANoble Gas 2CH 4 NH 3 H2OH2OHFNe 3 H2SH2SHClAr 4 HBrKr 5 HIXe A diatomic molecule contains only two atoms:H 2, N 2, O 2, Br 2, HCl, CO An ion is an atom, or group of atoms, that has a net positive or negative charge. cation – ion with a positive charge. If a neutral atom loses one or more electrons, it becomes a cation. Na:11 protons, 11 electronsNa + :11 protons, 10 electrons anion – ion with a negative charge. If a neutral atom gains one or more electrons, it becomes an anion. Cl:17 protons, 17 electronsCl - :17 protons, 18 electrons A monatomic ion contains only one atom: Na +, Cl -, Ca 2+, O 2-, Al 3+ A polyatomic ion contains more than one atom: OH -, CN -, NH 4 +, NO 3 - How many protons and electrons are in ? Al 27 13 3+ 13 protons, 13 – 3 = 10 electrons How many protons and electrons are in ? Se 78 34 2- 34 protons, 34 + 2 = 36 electrons Common ions: 1A: Li +, Na +, K + 2A: Mg 2+, Ca 2+, Ba 2+ 3A: Al 3+ 6A: O 2- S 2- 7A: F -, Cl -, Br -, I - Other: Ag +, Fe 2+, Fe 3+, Co 2+, Zn 2+, Mn 2+ Simple ionic compounds: formed from metals + nonmetals Ionic compounds consist of a combination of cations and an anions. The most reactive metals and the most reactive nonmetals combine to form ionic compounds. NaCl, ZnO, Al 2 O 3 2.3

4. Molecular formula shows the exact number of atoms of each element in the smallest unit of a substance Empirical formula shows the simplest whole-number ratio of the atoms in a substance Molecular H 2 O C 6 H 12 O 6 O 3 N 2 H 4 Empirical H 2 O CH 2 O O NH 2 Naming Molecular compounds common names H 2 O, NH 3, CH 4, element further left in periodic table is 1 st if more than one compound can be formed from the same elements, use prefixes to indicate number of each kind of atom (The prefix of “mono” may be omitted for the first element.) Name first element first and last element ends in ide PF 5 phosphorus pentafluoride HCl hydrogen chloride N 2 O 4 dinitrogen tetraoxide Prefix: mono- di- tri- tetra- penta- hexa- hepta- octa- nona- deca- Meaning: 1 2 3 4 5 6 7 8 9 10 Examples: SO 2 sulfur dioxide NF 3 nitrogen trifluoride N 2 O dinitrogen oxide Formula of Ionic Compounds The formula is always the same as the empirical formula because molecules don’t exist in ionic compounds Rules for writing formulas of ionic compounds: 1.The positive ion is given first in the formula 2.The subscripts in the formula must produce an electrically neutral formula unit 3.The subscripts should ne the set of smallest whole numbers possible 4.The charges on the ions are not included in the finished formula of the substance Cations: name of element Anions: change ending of element spelling to -ide 2.4

5. Formula of Ionic Compounds The sum of charges on the cations and anions in each formula unit must be zero. The subscript of cation is numerically equal to the charge on the anion; The subscript of anion is numerically equal to the charge on the cation; Al 2 O 3 Al 3+ O 2- +3 x 2 = +6, 3 x (-2) = -6 CaBr 2 Na 2 CO 3 +2 x 1 = +2, 2 x (-1) = -2 +1 x 2 = +2, 1 x (-2) = -2 Calcium bromide Sodium carbonate Aluminum oxide Mg(OH) 2 magnesium hydroxide Check Table 2.3 for the cations and anions Transition metal ionic compounds indicate charge on metal with Roman numerals FeCl 2 FeCl 3 +2 for Fe, Fe 2+ iron(II) chloride +3 for Fe, Fe 3+ iron(III) chloride Acids and Bases An acid can be defined as a substance that yields hydrogen ions (H + ) when dissolved in water. HCl Pure substance, hydrogen chloride Dissolved in water (H + Cl - ), hydrochloric acid Anions whose names end in “ide" form acids with “hydro-” prefix and “-ic” ending. H 2 S hydrosulfuric acid HCN hydrocyanic acid (CN - : cyanide) An oxoacid is an acid that contains hydrogen, oxygen, and another element. HNO 3 nitric acid H 2 CO 3 carbonic acid H 2 SO 4 sulfuric acid HClO 3 chloric acid 2.5

6. 2.6 1.Addition of one O atom to “-ic” acid  ”per…ic”acid HClO 4 perchloric acid 2. Removal of one O atom from “-ic” acid  ”-ous” acid HNO 2 nitrous acid 3. Removal of two O atoms from “-ic” acid  ”hypo…ous” acid HClO hypochlorous acid AcidAnion HClOhypochlorous acidClO - hypochlorite HClO 2 chlorous acidClO 2 - chlorite HClO 3 chloric acidClO 3 - chlorate HClO 4 perchloric acidClO 4 - perchlorate A base can be defined as a substance that yields hydroxide ions (OH - ) when dissolved in water. KOH potassium hydroxide Ba(OH) 2 barium hydroxide Hydrates: compounds that have a specific number of water molecules attached to them. BaCl 2 2H 2 O barium chloride dihydrate MgSO 4 7H 2 Omagnesium sulfate heptahydrate CuSO 4 5H 2 O blue CuSO 4 white Name the following compounds: Cu(NO 3 ) 2 KH 2 PO 4 NH 4 ClO 3 Copper(II) nitratepotasium dihydrogen phosphateammonium chlorate Common names of some compounds: H 2 ONH 3 CO 2 NaClNaHCO 3 Water ammonia dry ice table saltbaking soda solid carbon dioxide sodium chloride sodium hydrogen carbonate Some more listed in Table 2.7