Molecules, Compounds & Chemical Equations
Bonding Two (or more) atoms will bond together because the combined product is more stable than the individual atoms. The atoms combine or bond by sharing electrons and forming covalent bonds, or transferring electrons to for ionic bonds.
Covalent Bonds When electrons are shared between atoms, a molecule is formed. The arrangement of the atoms and bonds in the molecule will have a great effect on the properties of the molecule.
Homonuclear Diatomic Elements Some elements exist in nature as molecules. Common elements that exist bonded together by covalent bonds are: H 2, N 2, O 2, F 2, Cl 2, Br 2, and I 2
Covalent Bonds - Chlorine Covalent bonds occur between nonmetals. Electrons are shared, and the shared electrons hold the atoms together so they function as a unit called a molecule.
Elements & Compounds
Ionic Bonding When metals combine with non-metals, a transfer of electrons occurs, from the metal to the non-metal. The resulting attraction between oppositely charged ions is called an ionic bond. Although this attraction is very strong, the ions can be separated when dissolved in substances such as water.
Types of Bonds In ionic bonding, the coulombic attraction between oppositely charged ions in a crystal, forms very stable compounds.
Ionic Bonding The strength of ionic bonds comes from the crystal structure. Every cation is surrounded by anions, and every anion is surrounded by cations. The resulting coulombic attraction between oppositely charged ions creates very stable substances.
Ionic Bonding Lattice Energy is a measure of the strength of ionic bonding in a crystal. It is the energy change that takes place when gaseous ions come together to form a mole of an ionic solid. M+(g) + X-(g) MX(s)
Ionic Bonding Ionic bonds result from the electrostatic attraction of oppositely charged ions. There is no electron sharing between ions.
Ionic Bonding Electrons are transferred from the metal to the non-metal, creating ions. The oppositely charged ions attract each other, forming ionic bonds.
Electron Configurations of Ions The atoms of the main group elements (groups IA-VIIA) will form ions by losing or gaining electrons. The resulting ion will have the same electron configuration as a noble gas (group VIIIA). These configurations are usually very stable.
Common Ionic Charges The charges of ions of elements in groups 1 A-7 A (the main groups) are usually predictable. Group 1 A metals form +1 ions, group 2 A metals form +2 ions, etc. The non-metals of group 5 A have a -3 charge, those of group 6 A have a -2 charge, and the halogens form ions with a -1 charge.
Typical Ionic Charges
Naming Inorganic Compounds 1. Binary Compounds Binary compounds contain only two elements. The elements are either a metal with a nonmetal (ionic bonding), or two non-metals (covalent bonding).
Naming Binary Compounds a) Metal + Non-metal: When metals react with non-metals, the metal loses electrons and the non-metal gains electrons. The resulting attraction between oppositely charged ions creates ionic bonds.
Common Ionic Charges The charges of ions of elements in groups 1 A-7 A (the main groups) are usually predictable. Group 1 A metals form +1 ions, group 2 A metals form +2 ions, etc. The non-metals of group 5 A have a -3 charge, those of group 6 A have a -2 charge, and the halogens form ions with a -1 charge.
Typical Ionic Charges
Naming Binary Compounds For example, Na. Cl is called sodium chloride Where “chlor” is the root for the element chlorine.
Naming Binary Compounds Three common transition metals also have only one ionic charge, and are also named the same way. They are: zinc ion (always +2), silver ion (+1) and cadmium ion (+2) Zn. S is zinc sulfide, as “sulf” is the root for sulfur.
Writing Formulas of Binary Compounds have no net charges, so the formulas of ionic compounds must contain equal numbers of positive and negative charges. Magnesium bromide, made from magnesium ion (Mg 2+) and bromide ion (Br 1 -) has the formula Mg. Br 2
Binary Compounds with Variable Charge Metals Most transition metals and the metals on the lower right side of the periodic table can have several ionic charges. The properties of the ion vary greatly with charge, so the charge must be specified in naming the ion or its compounds.
Typical Ionic Charges
Binary Compounds with Variable Charge Metals
Binary Compounds with Variable Charge Metals If an ion has variable charges, you must specify the charge in naming the metal. If an ion has only one charge, it is incorrect to specify its charge.
Naming Fe 2 O 3 n Fe 2 O 3 is an iron oxide, but we must specify the charge of the iron ion. We know each oxide has a -2 charge, so three oxide ions have a total charge of -6. The two iron ions therefore have a charge of +6, with each iron having a charge of +3. The name of the compound is iron(III) oxide.
Naming Covalent Binary Compounds b) When two non-metals form a compound, they share electrons, rather than transfer them. The resulting bond is called a covalent bond. The naming of these compounds is fairly simple. The first element is named first, and the second element is named as the root + ide. Prefixes are used to indicate the number of each atom present.
Naming Covalent Binary Compounds These prefixes are used only for compounds containing two nonmetals. The prefix mono is never used for the first element in the compound.
Naming Covalent Binary Compounds n The prefix mono is never used for the first element. CO 2 is carbon dioxide. n If the prefix ends in an a or o, and the element that follows begins with a vowel, the last letter of the prefix is usually dropped. N 2 O 5 is called dintrogen pentoxide (and not pentaoxide).
Naming Covalent Binary Compounds n Note that these prefixes are only used for binary covalent compounds. It is incorrect to use them for compounds containing a metal and a nonmetal.
Naming Binary Compounds c) Naming of Binary Acids Binary acids are aqueous solutions of compounds with the general formula HX, where X represents a non-metal. When hydrogen forms compounds with nonmetals, the bonds are always covalent, with electrons shared between the two elements.
Naming Binary Acids The naming of the pure compound and its aqueous acid solution differ. HCl is a gas called hydrogen chloride. HCl(aq) is an acid called hydrochoric acid.
Naming Binary Acids n Name the following acids: H 2 S(aq) , HBr(aq)
Unusual Ions Mercury forms two ions, mercury(I) and mercury(II). The mercury(I) ion is polyatomic, and exists as two mercury(I) ions bonded together. Its formula is Hg 22+. Oxygen in compounds usually exists as the oxide ion, O 2 -. Oxygen also exists as the peroxide ion, O 22 -, with each oxygen having a -1 charge.
Naming Polyatomic Ions There are many ions, such as sulfate or nitrate, that contain more than one element. Many of these ions contain oxygen and a non -metal. These ions can be found in a group of acids called the oxy acids.
Naming the Oxy Acids The easiest way to learn the names of the ions is to memorize a short list of oxy acid names and their formulas. The names of the ions are derived from the names of the acids. Keep in mind that the acids must be aqueous solutions.
Common Oxy Acids Acid HNO 3 Name H 2 SO 4 Sulfuric acid HCl. O 3 Chloric acid (or iodic or bromic acid) H 3 PO 4 Phosphoric acid H 2 CO 3 Carbonic acid Nitric acid
Naming Complex Ions Once the list of acids is learned, the names of other acids and ions can be derived. Removal of the hydrogens in the acid as H+ ions results in ions that end in ate. HNO 3 minus one H+ ion gives NO 31 -, the nitrate ion. The oxy acids that end in ic, produce ions that end ate.
Naming Complex Ions Sulfuric acid is H 2 SO 4. Removing two H+ ions produces SO 42 -, the sulfate ion. Keep in mind that the formula of the ions must include the charge. If only one of the H+ ions is removed from sulfuric acid, HSO 41 - is produced. This is called the hydrogen sulfate ion, also commonly known as the bisulfate ion.
Naming Complex Ions Carbonic acid, H 2 CO 3, produces two ions: HCO 31 -, the hydrogen carbonate or bicarbonate ion and CO 32 -, the carbonate ion
Naming Complex Ions Some of the oxy acids previously listed also exist with one more oxygen in the formula. HCl. O 3, HBr. O 3 and HIO 3 , in aqueous solution are chloric, bromic and iodic acid respectively. Adding an oxygen to the formulas provides the formulas for the per root ic acid. HCl. O 4 is perchloric acid. The ion, Cl. O 41 - is the perchlorate ion.
Naming Complex Ions Several of the oxy acids listed previously can have one less oxygen atom in the formula. These acids have names that end in ous, and ions that end in ite. HNO 3 is nitric acid. HNO 2(aq) is nitrous acid. The ion NO 21 - is the nitrite ion.
Naming Complex Ions Sulfuric acid, phosphoric acid, chloric, bromic and iodic acids all can have one less oxygen atom. The acids are sulfurous acid, phosphorous acid, chlorous acid, bromous acid and iodous acid. The ions are called sulfite, phosphite, chlorite, bromite and iodite ion.
Naming Complex Ions The halogen oxy acids HCl. O 3, HBr. O 3, and HIO 3 also exist with two less oxygen atoms in the formula. The name of the resulting acid has the name hypo root ous acid. HCl. O(aq) is hypochlorous acid, and Cl. O 1 - is the hypochlorite ion.
Naming Complex Ions n If you memorize the list of acids ending in ic, you can derive the names and formulas for many other acids and ions. Acid HNO 3 H 2 SO 4 HCl. O 3 H 3 PO 4 H 2 CO 3 Name Nitric acid Sulfuric acid Chloric acid (or iodic or bromic acid) Phosphoric acid Carbonic acid
Naming Complex Ions In naming the ions from the acids on the list, remember that ic ate. n If there is one additional oxygen atom, the acid has the name per root ic, and the ion has the name per root ate. n If there is one less oxygen atom, the acid has a name ending in ous. The ions will have names ending in ite. (ous ite) n
Naming Complex Ions n If an acid has two less oxygen atoms than the “ic” list, its name has the form hypo root ous. The ion will have the name hypo root ite.
Other Common Formulas CH 3 COOH CH 3 COO 1 NH 3 NH 4+ OH 1 H 3 O+ Mn. O 41 Cr. O 42 Cr 2 O 72 - Acetic acid Acetate ion Ammonia Ammonium ion Hydroxide ion Hydronium ion Permanganate ion Chromate ion Dichromate ion
Chemical Composition Chemical composition can be expressed in several ways, including percentages by mass, or chemical formulas. For example, water contains 11. 2% hydrogen and 88. 8% oxygen by mass. This information must be consistent with the chemical formula for water, H 2 O.
Chemical Composition For example, water contains 11. 2% hydrogen and 88. 8% oxygen by mass. This information must be consistent with the chemical formula for water, H 2 O. 2 H atoms = 2(1. 008 amu) = 2. 016 amu 1 O atom =1( 16. 00 amu) =16. 00 amu molecular mass of water = 18. 02 amu % H = (2. 016/18. 02) x 100% = 11. 19%H % O = (16. 00/18. 02) x 100% = 88. 79%O
Chemical Composition The early scientists analyzed new chemical compounds to determine their composition and chemical formulas. Modern analytical laboratories still provide this service.
Chemical Composition Usually, the compound is combusted in the presence of oxygen. Any carbon in the compound is collected as carbon dioxide (CO 2), and any hydrogen is collected as water (H 2 O).
Chemical Composition Similar techniques exist to analyze for other elements. The formula obtained for the compound is the simplest whole number ratio of the elements in the compound, or the empirical formula. It may differ from the actual formula. For example, hydrogen peroxide is H 2 O 2, but chemical analysis will provide an empirical formula of HO.
Determining Empirical Formulas If given % composition: 1. Assume a quantity of 100 grams of the compound. 2. Determine the number of moles of each element in the compound by dividing the grams of each element by the appropriate atomic mass. 3. To simplify the formula into small whole numbers, divide the moles of each element by the smallest number of moles.
Determining Empirical Formulas 4. If necessary, multiply each number of moles by a factor that produces whole number subscripts. 5. If you know the approximate molar mass of the compound, determine the molecular formula.
% Composition Problem n An oxide of titanium contains 59. 9% titanium. Determine the empirical formula of the compound.
Determining Empirical Formulas If given combustion data: The ultimate goal is to get the simplest whole number ratio of the elements in the compound. Usually the compound contains carbon, hydrogen and perhaps oxygen or nitrogen. 1. Use the information about CO 2 to determine the moles and mass of carbon in the compound.
Determining Empirical Formulas If given combustion data: 2. Use the information about H 2 O to determine the moles and mass of hydrogen in the compound. 3. The mass and moles of oxygen (or a third element) can be obtained by difference. 4. Once moles of each element is obtained, find the relative number of moles and empirical formula (as with % composition).
Formulas from Combustion Data This method assumes the compound contains only C and H.
Empirical Formula using Combustion Data- Problem n A compound, which contains C, H and O, is analyzed by combustion. If 10. 68 mg of the compound produces 16. 01 mg of carbon dioxide and 4. 37 mg of water, determine the empirical formula of the compound. If the compound has a molar mass of 176. 1 g/mol, determine the molecular formula of the compound.
Stoichiometry is a Greek word that means using chemical reactions to calculate the amount of reactants needed and the amount of products formed. n Amounts are typically calculated in grams (or kg), but there are other ways to specify the quantities of matter involved in a reaction. n
Stoichiometry A balanced chemical equation or reaction is needed before any calculations can be made. The formulas of all reactants and products are written before attempting to balance the equation.
Balancing Chemical Equations. Problem n Sodium metal reacts with water to produce aqueous sodium hydroxide and hydrogen.
Balancing Chemical Equations. Problem n Sodium metal reacts with water to produce aqueous sodium hydroxide and hydrogen. Na(s) + H 2 O(l )
Balancing Chemical Equations. Problem n Sodium metal reacts with water to produce aqueous sodium hydroxide and hydrogen. Na(s) + H 2 O(l ) Na. OH(aq) + H 2(g)
Balancing Chemical Equations. Problem n Sodium metal reacts with water to produce aqueous sodium hydroxide and hydrogen. Na(s) + H 2 O(l ) Na. OH(aq) + H 2(g) n The equation is not yet balanced. Hydrogens come in twos on the left, and three hydrogens are on the right side of the equation.
Balancing Chemical Equations. Problem n Sodium metal reacts with water to produce aqueous sodium hydroxide and hydrogen. Na(s) + H 2 O(l ) Na. OH(aq) + H 2(g) n Try a “ 2” in front of the water.
Balancing Chemical Equations. Problem n Sodium metal reacts with water to produce aqueous sodium hydroxide and hydrogen. Na(s) + 2 H 2 O(l ) Na. OH(aq) + H 2(g) n We now have two O atoms on the left, so we need to put a 2 before Na. OH.
Balancing Chemical Equations. Problem n Sodium metal reacts with water to produce aqueous sodium hydroxide and hydrogen. Na(s) + 2 H 2 O(l ) 2 Na. OH(aq) + H 2(g) n The two sodium atoms on the right require that we put a 2 in front of Na on the left.
Balancing Chemical Equations. Problem n Sodium metal reacts with water to produce aqueous sodium hydroxide and hydrogen. 2 Na(s) + 2 H 2 O(l ) 2 Na. OH(aq) + H 2(g) n The two sodium atoms on the right require that we put a 2 in front of Na on the left. The equation is now balanced.
Balancing Chemical Equations. Problem n Sodium metal reacts with water to produce aqueous sodium hydroxide and hydrogen. 2 Na(s) + 2 H 2 O(l ) 2 Na. OH(aq) + H 2(g) Left Side Right Side Na- 2 H- 4 O- 2
Chemical Equations 2 Na(s) + 2 H 2 O(l ) 2 Na. OH(aq) + H 2(g) The balanced chemical equation can be interpreted in a variety of ways. It could say that 2 atoms of sodium react with 2 molecules of water to produce 2 molecules of sodium hydroxide and a molecule of hydrogen.
Chemical Equations 2 Na(s) + 2 H 2 O(l ) 2 Na. OH(aq) + H 2(g) The balanced chemical equation can be interpreted in a variety of ways. It could say that 200 atoms of sodium react with 200 molecules of water to produce 200 molecules of sodium hydroxide and 100 molecules of hydrogen.
Chemical Equations 2 Na(s) + 2 H 2 O(l ) 2 Na. OH(aq) + H 2(g) The balanced chemical equation can be interpreted in a variety of ways. n It is usually interpreted as 2 moles of sodium will react with 2 moles of water to produce 2 moles of sodium hydroxide and 1 mole of hydrogen. n The balanced equation tells us nothing about the masses of reactants or products.
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