TEKS 7B: Write the chemical formulas of common polyatomic ions, ionic compounds containing main group or transition metals, covalent compounds, acids, and bases. What are the formulas for some polyatomic ions? A polyatomic ion consists of a tightly bound group of atoms that behaves as a unit and carries a positive or negative charge. For example, the ammonium ion, which consists of one nitrogen atom and four hydrogen atoms and carries a 1+ charge, has the following formula: NH 4 + Examples of common polyatomic ions are shown in the table that follows. Notice that many of the names of the ions end in -ite and -ate. Notice also that three ions—the cyanide anion (CN – ), the hydroxide anion (OH – ), and the ammonium cation (NH 4 + ) shown above—have endings that differ from the others. (contd.)

TEKS 7B: Write the chemical formulas of common polyatomic ions, ionic compounds containing main group or transition metals, covalent compounds, acids, and bases.

To write the formulas for polyatomic ions, become familiar with the information and patterns in the table. For example, ions that end in -ite and -ate contain some number of oxygen atoms. Here are the nitrite and nitrate ions. -ite-ate NO 2 – NO 3 – Notice that these ions consist of the same elements—nitrogen and oxygen— but each has a different number of oxygen atoms. The ion that ends in - ite has one less oxygen atom than the ion that ends in -ate. Look for similar pairs of ions in the table. You can also see ions that begin with H, as in the example HCO 3 –. In these ions, think of the H as the ion H + that combined with another polyatomic ion. Here the other ion is the carbonate ion. H + + CO 3 2–  HCO 3 – carbonate hydrogen carbonate (contd.)

TEKS 7B: Write the chemical formulas of common polyatomic ions, ionic compounds containing main group or transition metals, covalent compounds, acids, and bases. The charge on the new ion, in this case hydrogen carbonate, is the algebraic sum of the ionic charges of the two component ions: (1+) + (2–) = 1–. 1. Write Formulas Write the chemical formulas for the following common polyatomic ions: ethanoate, dihydrogen phosphate, sulfite, dichromate.

TEKS 7B: Write the chemical formulas of common polyatomic ions, ionic compounds containing main group or transition metals, covalent compounds, acids, and bases. How are formulas for common ionic compounds written? Ionic compounds are formed from a metallic cation and a nonmetallic anion. One or both of these ions may be ions of single elements, or they may be polyatomic ions formed of more than one element. The metallic ion in an ionic compound may be a main group metal, such as the elements from Group 1A or 2A of the periodic table. These metals form cations of only one positive charge, for example, K + ions. Alternatively, the metallic ion may be one of an element that forms cations with different ionic charges. Many of these elements are transition metals—metals from the B group of elements—for example, iron, which forms Fe 2+ and Fe 3+ ions. Tin (Sn) and lead (Pb) also form cations of more than one charge. (contd.)

TEKS 7B: Write the chemical formulas of common polyatomic ions, ionic compounds containing main group or transition metals, covalent compounds, acids, and bases. Follow the rules below to write the formula of an ionic compound. Write the formula of the cation followed by the formula of the anion. Add subscripts as needed to balance the charges. If the metal forms cations of more than one charge, use the Roman numeral after the element name to determine the positive charge. Be sure the subscripts are in the lowest whole-number ratio. Subscripts with a value of 1 are not written. For example, lithium sulfide consists of Li + ions and S 2– ions. The charges will balance if there are two lithium ions for every one sulfide ion, so the chemical formula for lithium sulfide is Li 2 S. Alternatively, you can use the crisscross method to determine the subscripts. In this method, the value of the charge becomes the subscript for the other ion. (contd.)

TEKS 7B: Write the chemical formulas of common polyatomic ions, ionic compounds containing main group or transition metals, covalent compounds, acids, and bases. The numerical value of the charge of each ion is crossed over and becomes the subscript (without the sign) for the other ion. The overall charge of the formula is zero. Again, the subscripts are written in the lowest whole-number ratio. 2. Write Formulas Write the chemical formulas for the following ionic compounds containing main group or transition metals: iron(II) chloride, sodium iodide, sodium carbonate, copper(II) iodide.

TEKS 7B: Write the chemical formulas of common polyatomic ions, ionic compounds containing main group or transition metals, covalent compounds, acids, and bases. How are formulas for covalent compounds written? Covalent compounds consist of molecules that are made of atoms bonded together by covalent bonds. Many covalent compounds consist of only two elements. Unlike ionic compounds, both elements in covalent compounds are nonmetals, and the atoms do not form ions. Often, two nonmetals can combine in different ratios, forming more than one compound, for example, carbon monoxide (CO) and carbon dioxide (CO 2 ). When writing formulas for covalent compounds, use the prefixes in the name to tell you the subscript of each element in the formula. If the first element in the name of the compound has a subscript of 1, the prefix is omitted. (contd.)

TEKS 7B: Write the chemical formulas of common polyatomic ions, ionic compounds containing main group or transition metals, covalent compounds, acids, and bases. Prefixes used in naming covalent compounds are listed below: mono-1hexa-6 di-2hepta-7 tri-3octa-8 tetra-4nona-9 penta- 5deca-10 So, for example, the formula for carbon tetrachloride is CCl Write Formulas Write the chemical formulas for the following common covalent compounds: phosphorus pentachloride, chlorine trifluoride, iodine dioxide, dinitrogen pentoxide.

TEKS 7B: Write the chemical formulas of common polyatomic ions, ionic compounds containing main group or transition metals, covalent compounds, acids, and bases. How are formulas for acids and bases written? Formulas of Acids If you know the name of an acid, you can write its formula by using the guidelines for writing the name of an acid, in reverse. Use the table below as reference. Naming Common Acids Anion EndingExampleAcid NameExample -idechloride, Cl – hydro-(stem)-ichydrochloric acid -itesulfite, SO 3 – (stem)-ous acidsulfurous acid -atenitrate, NO 3 – (stem)-ic acidnitric acid (contd.)

TEKS 7B: Write the chemical formulas of common polyatomic ions, ionic compounds containing main group or transition metals, covalent compounds, acids, and bases. When the name of the acid begins with the prefix hydro- and has the suffix -ic, the anion is a single element. For example, the chemical formula for hydrochloric acid is HCl. When the name of the acid does NOT begin with the prefix hydro- but has the suffix -ic, the anion is a polyatomic ion with a name ending in -ate. For example, the chemical formula for nitric acid is HNO 3. When the name of the acid does NOT begin with the prefix hydro- but has the suffix -ous, the anion is a polyatomic ion with a name ending in -ite. For example, the chemical formula for sulfurous acid is H 2 SO 3. Subscripts are used to balance the charges of the H + cations and the anions when necessary. Subscripts of 1 are not written. (contd.)

TEKS 7B: Write the chemical formulas of common polyatomic ions, ionic compounds containing main group or transition metals, covalent compounds, acids, and bases. Formulas of Bases In general, bases are ionic compounds that produce hydroxide ions (OH – ) when dissolved in water. The chemical formula of a base consists of the symbol for the metal cation followed by the symbol for hydroxide. Use subscripts to balance the charges. For example, the formula for magnesium hydroxide is Mg(OH) Write Formulas Write the chemical formulas for each of the following acids and bases: carbonic acid, hydrosulfuric acid, barium hydroxide, ammonium hydroxide.