Chemistry I Naming Compounds and Writing Chemical Formulas Monatomic Ions Many main- group elements can lose or gain electrons to form ions. Ions formed from a single atom are known as monatomic ions. Example: To gain a noble- gas electron configuration, nitrogen gains three electrons to form N 3 ions. Some main- group elements tend to form covalent bonds instead of forming ions. Examples: carbon and silicon Naming Monatomic Ions Monatomic cations are identified simply by the element s name. Examples: K + is called the potassium cation Mg 2+ is called the magnesium cation For monatomic anions, the ending of the element s name is dropped, and the ending - ide is added to the root name. Examples: F is called the fluoride anion N 3 is called the nitride anion
Image Source: http://wps.prenhall.com/wps/media/objects/3310/3390185/imag0207/tb02_005.gif Binary Ionic Compounds Compounds composed of two elements are known as binary compounds. In a binary ionic compound, the total numbers of positive charges and negative charges must be equal. The formula for a binary ionic compound can be written given the identities of the compound s ions. Example: magnesium bromide Ions combined: Mg 2+, Br Chemical formula: MgBr2 A general rule to use when determining the formula for a binary ionic compound is crossing over to balance charges between ions. Example: aluminum oxide Write the symbols for the ions. Al 3+ O 2 Cross over the charges by using the absolute value of Al2O3 each ion s charge as the subscript for the other ion. Image Source: https://dr282zn36sxxg.cloudfront.net/datastreams/f- d%3a3cf31dd19f751490da9362b94a585ac3c903f9403c0bee22ba7099c9%2bimage%2bimage.1
Image Source: http://lindseylester.files.wordpress.com/2011/04/ionic- compounds.jpg Naming Binary Ionic Compounds The nomenclature, or naming system, or binary ionic compounds involves combining the names of the compound s positive and negative ions. The name of the cation is given first, followed by the name of the anion: Example: Al2O3 aluminum oxide Image Source: http://education- portal.com/cimages/multimages/16/naming- binary- ionic- compounds.jpg Naming Binary Ionic Compounds, Compounds Containing Polyatomic Ions Polyatomic Ion group of atoms with a charge Many common polyatomic ions are oxyanions polyatomic ions that contain oxygen. Image Source: m/mb/biochimie/chem/regents/reftables/polyatomicions.jpg
Naming Binary Ionic Compounds The Stock System of Nomenclature Some elements such as iron, form two or more cations with different charges. To distinguish the ions formed by such elements, scientists use the Stock system of nomenclature. The system uses a Roman numeral to indicate an ion s charge. Examples: Fe 2+ iron(ii) Fe 3+ iron(iii) Image Source: http://education- portal.com/cimages/multimages/16/ionic- compounds- with- transition- metals.jpg Naming Binary Molecular Compounds Unlike ionic compounds, molecular compounds are composed of individual covalently bonded units, or molecules (usually 2 nonmetals). The system of naming molecular compounds is based on the use of prefixes. The first element in the compound has a prefix only if there is more than one atom. The second element always has a prefix.
Image Source: http://images.slideplayer.us/6/1609890/slides/slide_4.jpg Oxidation Numbers To indicate the distribution of electrons among the atoms in a molecular compound or a polyatomic ion, oxidation numbers are assigned to the atoms. Rules for Assigning Oxidation Numbers 1. An atom in its elemental form has an oxidation number of zero. 2. Fluorine has an oxidation number of 1 in all of its compounds. 3. Oxygen has an oxidation number of - 2 unless it is combined with F, then it is +2. 4. Hydrogen can have an oxidation number of +1 or - 1. 5. Oxidation numbers must add to zero in a compound. Many elements can have more than one oxidation number. These numbers can be used in the same way as charges. Names of Common Acids Binary Acids (composed of 2 elements) HCl hydrochloric acid HBr hydrobromic acid HI hydroiodic acid HF hydrofluoric acid
Ternary/Oxyacids (composed of H, O, and a third element) H2SO4 Sulfuric Acid HNO3 Nitric Acid H2CO3 carbonic acid H3PO4 phosphoric acid Percentage Composition Percentage by mass of a particular element in chemical compound. Percentage composition formula: mass of element in sample of compound mass of sample of compound An empirical formula consists of element symbols with subscripts showing small whole- number mole ratios of the atoms in the compound. 1. Convert from grams to moles 2. Divide each number of moles by the smallest number in the existing ratio. 3. Write formula % element in compound 100 =