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Molecules, Compounds & Chemical Equations

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.

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Molecules, Compounds & Chemical Equations

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  1. Molecules, Compounds & Chemical Equations

  2. 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.

  3. 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.

  4. Homonuclear Diatomic Elements Some elements exist in nature as molecules. Common elements that exist bonded together by covalent bonds are: H2, N2, O2, F2, Cl2, Br2, and I2

  5. Covalent Bonds - Chlorine Covalent bonds occur between non-metals. Electrons are shared, and the shared electrons hold the atoms together so they function as a unit called a molecule.

  6. Elements & Compounds

  7. 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.

  8. Types of Bonds In ionic bonding, the coulombic attraction between oppositely charged ions in a crystal, forms very stable compounds.

  9. 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.

  10. 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)

  11. Ionic Bonding Ionic bonds result from the electrostatic attraction of oppositely charged ions. There is no electron sharing between ions.

  12. Ionic Bonding Electrons are transferred from the metal to the non-metal, creating ions. The oppositely charged ions attract each other, forming ionic bonds.

  13. 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.

  14. Common Ionic Charges The charges of ions of elements in groups 1A-7A (the main groups) are usually predictable. Group 1A metals form +1 ions, group 2A metals form +2 ions, etc. The non-metals of group 5A have a -3 charge, those of group 6A have a -2 charge, and the halogens form ions with a -1 charge.

  15. Typical Ionic Charges

  16. Naming Inorganic Compounds 1. Binary Compounds Binary compounds contain only two elements. The elements are either a metal with a non-metal (ionic bonding), or two non-metals (covalent bonding).

  17. 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.

  18. Common Ionic Charges The charges of ions of elements in groups 1A-7A (the main groups) are usually predictable. Group 1A metals form +1 ions, group 2A metals form +2 ions, etc. The non-metals of group 5A have a -3 charge, those of group 6A have a -2 charge, and the halogens form ions with a -1 charge.

  19. Typical Ionic Charges

  20. Naming Binary Compounds For example, NaCl is called sodium chloride Where “chlor” is the root for the element chlorine.

  21. 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) ZnS is zinc sulfide, as “sulf” is the root for sulfur.

  22. Writing Formulas of Binary Compounds 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 (Mg2+) and bromide ion (Br1-) has the formula MgBr2

  23. 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.

  24. Typical Ionic Charges

  25. Binary Compounds with Variable Charge Metals

  26. 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.

  27. Naming Fe2O3 • Fe2O3 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.

  28. 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.

  29. Naming Covalent Binary Compounds These prefixes are used only for compounds containing two non-metals. The prefix mono is never used for the first element in the compound.

  30. Naming Covalent Binary Compounds • The prefix mono is never used for the first element. CO2 is carbon dioxide. • 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. N2O5 is called dintrogen pentoxide (and not pentaoxide).

  31. Naming Covalent Binary Compounds • Note that these prefixes are only used for binary covalent compounds. It is incorrect to use them for compounds containing a metal and a non-metal.

  32. 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 non-metals, the bonds are always covalent, with electrons shared between the two elements.

  33. 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.

  34. Naming Binary Acids • Name the following acids: H2S(aq) , HBr(aq)

  35. 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 Hg22+. Oxygen in compounds usually exists as the oxide ion, O2-. Oxygen also exists as the peroxide ion, O22-, with each oxygen having a -1 charge.

  36. 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.

  37. 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.

  38. Common Oxy Acids AcidName HNO3 Nitric acid H2SO4 Sulfuric acid HClO3 Chloric acid (or iodic or bromic acid) H3PO4 Phosphoric acid H2CO3 Carbonic acid

  39. 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. HNO3 minus one H+ ion gives NO31-, the nitrate ion. The oxy acids that end in ic, produce ions that end ate.

  40. Naming Complex Ions Sulfuric acid is H2SO4. Removing two H+ ions produces SO42-, 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, HSO41- is produced. This is called the hydrogen sulfate ion, also commonly known as the bisulfate ion.

  41. Naming Complex Ions Carbonic acid, H2CO3, produces two ions: HCO31-, the hydrogen carbonate or bicarbonate ion and CO32-, the carbonate ion

  42. Naming Complex Ions Some of the oxy acids previously listed also exist with one more oxygen in the formula. HClO3, HBrO3 and HIO3 , 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. HClO4 is perchloric acid. The ion, ClO41- is the perchlorate ion.

  43. 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. HNO3 is nitric acid. HNO2(aq) is nitrousacid. The ion NO21- is the nitrite ion.

  44. 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.

  45. Naming Complex Ions The halogen oxy acids HClO3, HBrO3, and HIO3 also exist with two less oxygen atoms in the formula. The name of the resulting acid has the name hypo root ous acid. HClO(aq) is hypochlorous acid, and ClO1- is the hypochlorite ion.

  46. Naming Complex Ions • If you memorize the list of acids ending in ic, you can derive the names and formulas for many other acids and ions. AcidName HNO3 Nitric acid H2SO4 Sulfuric acid HClO3 Chloric acid (or iodic or bromic acid) H3PO4 Phosphoric acid H2CO3 Carbonic acid

  47. Naming Complex Ions • In naming the ions from the acids on the list, remember that ic ate. • If there is one additional oxygen atom, the acid has the name perrootic, and the ion has the name per root ate. • 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)

  48. Naming Complex Ions • If an acid has two less oxygen atoms than the “ic” list, its name has the form hypo rootous. The ion will have the name hyporootite.

  49. Other Common Formulas CH3COOH Acetic acid CH3COO1- Acetate ion NH3 Ammonia NH4+ Ammonium ion OH1- Hydroxide ion H3O+ Hydronium ion MnO41- Permanganate ion CrO42- Chromate ion Cr2O72- Dichromate ion

  50. 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, H2O.

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