Chapter 2 – Atoms, Molecules and Ions

Dalton Atomic Theory An element is composed of tiny, indivisible, indestructible particles called atoms. All atoms of an element are identical and have the same properties. Atoms of different elements combine to form compounds. Compounds contain atoms in small whole number ratios. Atoms can combine in more than one ratio for form different compounds.

Dalton Atomic Theory 1 & 2 of atomic theory were later proven incorrect Still, statements 3, 4, & 5 of atomic theory are still accepted today.

Thomson Model of the Atom Two subatomic particles were discovered. Negatively charged electrons, e–. Positively charged protons, p+. An electron has a relative charge of –1, and a proton has a relative charge of +1. Thomson proposed the plum pudding model of the atom.

Rutherford Model of the Atom When alpha particles were fired at thin gold foils, some of the alpha particles were deflected backwards by striking the dense nucleus. Most of the alpha particles passed through the foil because an atom is largely empty space. Atoms positive charge is concentrated in the nucleus. Neutrons, n0,were discovered by Chadwick. A neutron is about the size of a proton without any charge.

Subatomic Particles

Protons (p+) The number of protons equals the atomic number The proton has a positive charge. It hangs out in the nucleus, with the neutrons. Symbol The number of protons equals the atomic number

Atomic number, Mass number, and Isotopes Isotopes are atoms of the same element but have different number of neutrons. Atomic Number (Z) – number of protons in the nucleus Mass Number (A) – number of protons +number of neutrons

Isotopes Practice Ex: A certain isotope X contains 28 protons and 32 neutrons. What is the mass number of this isotope? Identify the element. Mass Number = 28+ 32 =60 Nickel The mass number is 51. Mass Number = # protons + # neutrons. Mass Number = 23 + 28 = 51. The element is vanadium.

Ions An ion is an atom or group of atoms that has a net positive or negative charge. Cation – positive ion (lost electrons) Ex: Na (p=11, e=11) Na + (p=11, e=11-1 =10) Anion – negative ion( gained electrons) Ex: O (p=8, e=8) O2- (p=8, e= 8+2= 10)

The Periodic Table

Groups and Periods of Elements A vertical column on the periodic table is a group or family of elements. A horizontal row on the periodic table is a period of elements. There are 18 groups and seven periods on the periodic table.

Valence Electrons When an atom undergoes a chemical reaction, only the outermost electrons are involved. Valence electrons: electrons on the outermost energy level involved in chemical reaction. Group IA/1 metals lose their one valence electron to form 1+ ions. Na → Na+ + e– Metals lose their valence electrons to form cations & nonmetals gain valence electrons to form anions.

Ionic Charges

IUPAC Nomenclature The International Union of Pure and Applied Chemistry, IUPAC, has set rules for naming compounds. These rules, referred to as IUPAC nomenclature, are still in use today for Inorganic compounds. Most inorganic compounds do not contain the element carbon with few exceptions.

Inorganic compounds There are five common classes of inorganic compounds: Binary ionic Ternary ionic Binary molecular Binary acid Ternary oxyacid

Classification of Compounds

Binary Ionic Compounds Binary ionic compounds contain two elements: metal and nonmetal. Formula Writing: Ex: K+1 Cl–1 KCl Ca+2 Br–1 Br–1  CaBr2 Naming: Monatomic cation named first and the anion second by taking the root of the element name and ending with ”ide”. Ex: KCl – potassium chloride CaBr2 - Calcium bromide

Binary Ionic Compounds (Transition metals) Roman numeral indicates the charge of the metal cation. Formula Writing: Ex: Cu+1 F–1 CuF Fe+3 Fe+3 O–2 O–2 O–2  Fe2O3 Naming: Ex: CuF – copper (I) fluoride Fe2O3 - Iron (III) oxide

Binary Covalent Compounds (two nonmetals) Prefixes are used to denote the numbers of atoms present. The first element in the formula is named first followed by the second element ending with “ide” using prefixes. Note: The prefix mono- is never used for naming the first element.

Covalent Compounds (naming) Ex: CO Carbon monoxide CO2 Carbon dioxide CCl4 Carbon tetrachloride N2O5 Dinitrogen pentaoxide

Ternary Ionic Compounds Ternary ionic compounds contain polyatomic ions. Formula Writing: Ex: Ca+2 Ca +2 Ca+2 (PO4) -3 (PO4) -3  Ca3(PO4)2 Naming: the cation name followed by the anion name. Ex:NaClO2 - sodium chlorite. CoCO3 - cobalt (II) carbonate

Binary Acids HF(aq) is hydrofluoric acid. HI(aq) is hydroiodic acid A binary acid is an aqueous solution of a compound containing hydrogen and a nonmetal. The name of an acid always begins with hydro and end with ic acid. Ex: HCl(aq) – hydrochloric acid HF(aq) is hydrofluoric acid. HI(aq) is hydroiodic acid

Ternary Oxyacids Ternary oxyacids are aqueous solutions of a compound containing hydrogen and an oxyanion. oxyanion ending with “ate” changed to ic acid. oxyanion ending with “ite” changed to ous acid. Ex: HNO2(aq) -nitrous acid (NO2–1 -nitrite ion). HNO3(aq) -nitric acid (NO3–1, nitrate ion). H2SO4(aq)