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CHEM 1100 (7)
Chapter 4


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CHEM 1100
Kim Bolton

CHAPTER 4 MOLECULES, COMPOUNDS, AND CHEMICAL REACTIONS • Molecules determine the behaviour of matter Chemical Compounds and Chemical Formulas • All matter is composed of atoms • Atoms are usually bound together to form compounds Chemical Formulas • Represent a compound with a chemical formula which indicates the elements present in the compound and the relative number of atoms of each • Ex. The chemical formula for table salt is NaCl and is composed of sodium and chlorine atoms in 1:1 ratio • Ex. H2O is chemical formula for water, showing it is composed of hydrogen and oxygen in 2:1 ratio • A subscript in a chemical formula indicates the relative number of each atom in the compound, they do not change for a given compound • Water will always be H 2; hydrogen peroxide is H O2 2 • When a group of atoms is placed in parentheses with a subscript outside of the parentheses, that subscript applies to the entire group of atoms • Ex. Ca(NO )3 2s 1 Ca, 2 N, 6 O Ionic and Molecular Compounds • Only few elements exist as isolated atoms with stable electron configurations (noble gases) • Elements with unstable electron configurations will usually form compounds with other elements to gain stability • 2 compounds: ionic and molecular Ionic Compounds • Compounds containing a metal and one or more non-metals are called ionic compounds • Metals have a tendency to lose electrons and that non-metals have a tendency to gain them • Metals and non-metals combine to form very stable compounds • Ionic bond when a metal and non-metal bond together a metal transfers some or all of its valence electrons to the non-metal, and both become stable • Ex. In sodium chloride sodium atoms lose an electron to form Na and chlorine gain an electron to form Cl-  The compound NaCl is held together by the attraction between positively charged sodium ions and negatively charged chlorine ions • When ionic compounds dissolve in water, they dissociate to form ions • Ex. Salt water does not contain NaCl units but contains Na and Cl ions CHAPTER 4 MOLECULES, COMPOUNDS, AND CHEMICAL REACTIONS • Solutions with dissolved ions are called electrolyte solutions and are good conductors of electricity due to mobility of the charged ions Molecular Compounds • Compounds containing only non-metals are called molecular compounds • Atoms share their electrons to gain stability  covalent bond • Unlike ionic compounds, which are composed of repeating positive and negative ions, molecular compounds are composed of clusters of two or more atoms bonded together to form molecules • Molecules are represented by a molecular formula • A molecular formula is a chemical formula that specifies the actual number of each kind of atom in the molecule, not just the simplest ratio • The bulk properties of molecular compound depend on the molecules that compose them; a slight change in the molecule has profound consequences • The molecule – its atoms, its shape, its structure and its bond is responsible for what we observe and experience Naming Compounds • H 2 is called dihydrogen monoxide or water • NH is called nitrogen trihydride or ammonia 3 Naming Ionic Compounds • Name for binary (two-element) ionic compounds: Name of cation (metal) base name of anion (nometal) + ide • Ex. NaCl sodium chloride MgO magnesium oxide Li2S lithium sulfide FeCl 3ron (III) chloride • Names of ionic compounds DO NOT contain prefixes such as di or tri to indicate the number of each type of atom • Ionic compounds that contain a transition metal include a Roman numeral indicating the charge of the metal Some Common Anions Non-metal Symbol for Base Anion Ion Name Name Fluorine F- Fluor Fluoride Chlorine Cl- Chlor Chloride CHAPTER 4 MOLECULES, COMPOUNDS, AND CHEMICAL REACTIONS Bromine Br- Brom Bromide Iodine I- Iod Iodide Oxygen O 2- Ox Oxide Sulfur S 2- Sulf Sulfide Nitrogen N 3- Nitr Nitride • Many ionic compounds contain anions with more than one atom  polyatomic ions • Use the name of the polyatomic ion as the name of the anion 3 • Ex. KNO cation=potassium anion=nitrate potassium nitrate Some Common Polyatomic Ions Name Formula Carbonate CO 3- Bicarbonate HCO 3- Hydroxide OH - - Nitrate NO 3 3- Phosphate PO 4
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