1 / 26

Writing formulas and naming compounds

Writing formulas and naming compounds. What is a chemical formula? It indicates the relative number of atoms of each kind in an ionic compound. Ex Al 2 O 3 has 2 atoms of Al and 3 atoms of O.

casimir-lel
Download Presentation

Writing formulas and naming compounds

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Writing formulas and naming compounds

  2. What is a chemical formula? • It indicates the relative number of atoms of each kind in an ionic compound. • Ex Al2O3 has 2 atoms of Al and 3 atoms of O. • It indicates the number of atoms of each element contained in a single molecule of a molecular compound. Ex. C8H18 has 8 atoms of carbon and 18 atoms of H in a molecule of octane.

  3. The first step in naming and writing formula is to determine if the compound is ionic or covalent. • There are different rules for naming and writing formulas for ionic and covalent compounds. • The compound is ionic if it is composed of a cation and an anion, or a metal and a nonmetal. The elements will be located on opposite sides of the periodic table. They have a high electronegativity difference. • The compound is covalent (or molecular) if both elements are nonmetals.

  4. Writing formulas for binary ionic compounds • Binary because composed of only 2 elements. • Ionic because composed of a metal and a nonmetal. • Example aluminum oxide.

  5. Rules for writing formulas for binary ionic compounds 1). Write the symbol and charge for the cation. 2). Write the symbol and charge for the anion. 3). Criss cross the oxidation numbers and drop the charges. The oxidation number will become the subscript for the other element. 4). Reduce the subscripts if possible. If they are the same, they cancel completely. 5). If the subscript is 1, do not write anything.

  6. Example: Write the formula for calcium iodide. • Write symbols and charges. • Ca+2 I-1 • Criss-cross oxidation numbers, drop charges. • Ca1I2 • Cancel and take away ones. • Answer: CaI2

  7. Question: Write the formula for Magnesium Oxide. • 1) Write the symbol and charge. • Mg+2 O-2 • 2) Criss cross oxidation number and drop charges. • Mg2O2 • 3). Cancel and don’t write 1’s. • Answer: MgO • Complete page 4 and the bottom of page 5 of formula writing packet.

  8. Naming Binary Ionic Compounds. • If a compound consists of a metal and a nonmetal, we use the name of the first element (always the cation) followed by the second element (always the anion). For the anion only, drop the last syllable and add –ide. Subscripts are not included in the name. Examples: CaO: calcium oxide LiCl: lithium chloride K2S: potassium sulfide

  9. Practice: Naming and Writing formulas of binary ionic compounds. • P. 223 sample problem A • P. 223 practice #1 a-e, and #2 a-f • Complete packet page 1 and 8.

  10. Using Roman numerals • Some elements, such as iron, form 2 or more cations with different charges. To distinguish the ions formed by such elements, scientists use the Stock system of nomenclature. This system uses a Roman numeral to indicate the ion’s charge. The numeral is enclosed in parentheses and placed immediately after the metal name. • Fe+2 is iron (II) and Fe+3 is iron (III) • Names of metals that commonly form only one cation, do not include a Roman numeral.

  11. Example: • CuCl2 • Determine the charges of each element, by writing ions side by side. • Backwards criss-cross to determine charge of cation. • Name by writing name of cation , roman numeral, name of anion with ide instead of last syllable. • Cu Cl-1 • Cu+2 Cl-1 • Copper(II) chloride

  12. Example of writing formulas with roman numerals • Example: Write the formula of lead(IV) oxide. • Write symbols with charge. • Pb+4 and O-2 • Criss cross and drop signs. • Pb2O4 • Reduce and remove 1’s. • PbO2

  13. Practice • Page 225 #1(a-f) and #2 (a-d) • Complete packet page 3 and 5(top)

  14. POLYATOMIC IONS A covalently bonded group of atoms that has a positive or negative charge and act as a unit is a polyatomic ion. The prefix poly means “many”. Most simple polyatomic ions are anions. Ammonium (NH4) is the only polyatomic cation. Sometimes there are parentheses in the formula, so you can tell its polyatomic.

  15. Naming compounds containing polyatomic ions • If it contains a polyatomic ion, it is ionic, so it follows the rules for naming ionic compounds. • If anion is polyatomic, do not change the ending to ide. Keep it the same as is listed on the chart. Name cation then name anion. • If the cation is polyatomic and the anion is binary, name is just like before. The ide ending means the anion is not polyatomic.

  16. Example • Al2(SO4)3 • Al+3 and SO4-2 • Aluminum sulfate • Fe(OH)2 • Fe+2 and OH-1 • Iron(II)hydroxide

  17. Writing formulas for polyatomic ionic compounds • 1. Write the symbols for the monatomic and polyatomic ions in the compound.  • 2. Look up the oxidation numbers of the ions involved. • If a single atom, use the periodic table. • If roman numeral (variable oxidation number) or polyatomic, use the chart. • 3. Criss cross the oxidation numbers, and drop the charges. • 4. Put polyatomic ions in parentheses if they have a subscript. • 5. Reduce (simplify) and erase ones. • 6. DO NOT ADD< SUBTRACT, MULTIPLY, OR DIVIDE. Just criss cross and reduce if necessary!

  18. Example • Write the formula for Lead (II) hydroxide. • 1. Write the symbol and oxidation number. • Pb+2 OH-1 • 2. Criss cross charges and drop signs. • Pb1 OH2 • 3. Use parentheses if needed. • Pb1(OH)2 • 4. Reduce and drop 1’s. • Pb(OH)2

  19. Another example • Write the formula for ammonium sulfate. • 1. Write the symbol and oxidation number. • NH4+1 SO4-2 • 2. Criss cross charges and drop signs. Use parentheses if needed. • (NH4)2 (SO4)1 • 3. Reduce and drop 1’s. • (NH4)2 (SO4)

  20. Naming Molecular formulas (covalent) • Molecular/covalent compounds are made of 2 nonmetals. • Generally, the most metallic element is written first. These elements are farther to the left in the periodic table. If both elements are in the same group, the more metallic element is closer to the bottom of the group. • The name of the second element is changed to -ide. • Because molecular formulas can combine in many combinations, prefixes are used to indicate the subscript. Do not criss cross and do not use oxidation numbers. • Don’t use mono on first element.

  21. Prefixes • 1- mono • 2- di • 3- tri • 4- tetra • 5- penta • 6- hexa • 7- hepta • 8- octa • 9- nona • 10- deca

  22. Examples • P2O5 • Prefix of 1st element, name of 1st element • Prefix of 2nd element, name of 2nd element, change ending to ide. • Diphosphorus pentaoxide • CO • Carbon monoxide • (Don’t write mono on first element.)

  23. Writing molecular formulas • Write the symbols for the elements in the order that they appear in the name. • The prefixes indicate the number of atoms of each element in the molecule. • The prefixes appear as subscripts in the formulas. • If there is no prefix, there is only one atom. (1st element only) • Remember, do not criss cross. • Example tetraphosphorus dichloride • P4Cl2

  24. REVIEW SHEET ***1ST PUT I (ionic) OR C (covalent) BESIDE THE QUESTION FRONT LEFT COLUMN: 1—20, 25, 26 FRONT RIGHT COLUMN: 1—18, 23, 25, 26

  25. Examples-I ateice cream. It was delicious. • HCl • This is binary, H and Cl. Follow rule #1. • Hydrochloric acid • H2SO4- This is polyatomic. Hydrogen and sulfate (SO4)-2. Must find polyatomic anion and name. Ending is -ate so change to -ic. • Sulfuric acid (notice no hydro, hydro is only for binary acids). • HNO2- Polyatomic, H and nitrite. -ite becomes –ous. Nitrous acid.

  26. Writing formulas for acids • Cation is always H+1. From the name of the acid, you can figure out the anion. • Write symbols and charges for cation and anion. • Criss cross oxidation numbers and drop signs. • Reduce and drop 1’s. • Example • Phosphoric acid • H+1 and phosphoric so phosphate, so • H+1 and (PO4)-3 • H3PO4

More Related