Atoms, Molecules and Ions Chapter 2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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, having the same size, mass and chemical properties. 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. (Law of Definite Proportions) The ratio of the atoms in any compound is either an integer or a simple fraction. (Law of Multiple Proportions) 4.A chemical reaction involves only the separation, combination, or rearrangement of atoms; it does not result in their creation or destruction. 2.1

2 Dalton’s Atomic Theory

8 X 2 Y 16 X8 Y + 2.1

atomic radius ~ 100 pm = 1 x m nuclear radius ~ 5 x pm = 5 x m Rutherford’s Model of the Atom ?v=XBqHkraf8iE

2.2 om/watch ?v=EV1ow O1H2dA

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 2.3 Atomic number, Mass number and Isotopes

2.3 The Isotopes of Hydrogen U U Isotopes are atoms of the same element (X) with different numbers of neutrons in their nuclei

6 protons, 8 (14 - 6) neutrons, 6 electrons 6 protons, 5 (11 - 6) neutrons, 6 electrons Do You Understand Isotopes? 2.3 How many protons, neutrons, and electrons are in C 14 6 ? How many protons, neutrons, and electrons are in C 11 6 ?

Period Group Alkali Metal Noble Gas Halogen Alkaline Earth Metal 2.4 The periodic table

Molecules and ions

Molecular Compound H2H2 H2OH2ONH 3 CH 4 A diatomic molecule contains only two atoms:H 2, N 2, O 2, Br 2, HCl, CO A polyatomic molecule contains more than two atoms:O 3, H 2 O, NH 3, CH 4 2.5

cation – ion with a positive charge If a neutral atom loses one or more electrons, it becomes a cation. anion – ion with a negative charge If a neutral atom gains one or more electrons, it becomes an anion. An ion is an atom, or group of atoms, that has a net positive or negative charge. Na 11 protons 11 electrons Na + 11 protons 10 electrons Cl 17 protons 17 electrons Cl - 17 protons 18 electrons 2.5 A monatomic ion contains only one atom:Na +, Cl -, Ca 2+, O 2-, Al 3+, N 3- A polyatomic ion contains more than one atom:OH -, CN -, NH 4 +, NO 3 -

13 protons, 10 (13 – 3) electrons 34 protons, 36 (34 + 2) electrons Do You Understand Ions? 2.5 How many protons and electrons are in ?Al How many protons and electrons are in ?Se

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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

A molecular formula shows the exact number of atoms of each element in the smallest unit of a substance An empirical formula shows the simplest whole-number ratio of the atoms in a substance H2OH2O H2OH2O molecularempirical C 6 H 12 O 6 CH 2 O O3O3 O N2H4N2H4 NH molecular formula

Naming Molecular compounds common names H 2 O, NH 3, CH 4, element further left in periodic table is 1 st element closest to bottom of group 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; For oxides, the ending “a” in the prefix may be omitted.) Name first element first and last element ends in ide 2.7

HIhydrogen iodide NF 3 nitrogen trifluoride SO 2 sulfur dioxide N 2 Cl 4 dinitrogen tetrachloride NO 2 nitrogen dioxide N2ON2Odinitrogen monoxide Molecular Compounds 2.7 TOXIC ! Laughing Gas

The formula is always the same as the empirical formula because molecules don’t exit in ionic compounds 2.6 Formula of Ionic Compounds

2.6 Al 2 O 3 2 x +3 = +63 x -2 = -6 Al 3+ O 2- CaBr 2 1 x +2 = +22 x -1 = -2 Ca 2+ Br - Na 2 CO 3 1 x +2 = +21 x -2 = -2 Na + CO 3 2- 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;

–cation: name of element –anion (nonmetal), add “ide” to element name BaCl 2 barium chloride K2OK2O potassium oxide Mg(OH) 2 magnesium hydroxide KNO 3 potassium nitrate 2.7 Naming Ionic Compounds Group 1A (Li, Na etc.), 2A metals (Mg,Ca,etc.), aluminum, zinc have only one type of charge when forming ionic compounds.

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Transition metal ionic compounds –indicate charge on metal with Roman numerals FeCl 2 2 Cl - -2 so Fe is +2 iron(II) chloride FeCl 3 3 Cl - -3 so Fe is +3 iron(III) chloride Cr 2 S 3 3 S so Cr is +3 (6/2)chromium(III) sulfide 2.7

Worked Example 2.5

2.7 Steps of naming ionic and binary molecular compounds

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 2.7 Acids and Bases Anions whose names end in “ide" form acids with “hydro-” prefix and “-ic” ending.

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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 2.7 HNO 3 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 HClO 3 chloric acid

2.7

A base can be defined as a substance that yields hydroxide ions (OH - ) when dissolved in water. NaOH sodium hydroxide KOH potassium hydroxide Ba(OH) 2 barium hydroxide 2.7

Hydrates are compounds that have a specific number of water molecules attached to them. BaCl 2 2H 2 O 2.7 LiClH 2 O MgSO 4 7H 2 O Sr(NO 3 ) 2 4H 2 O barium chloride dihydrate lithium chloride monohydrate magnesium sulfate heptahydrate strontium nitrate tetrahydrate CuSO 4 5H2O CuSO4

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