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4.2: Names and Formulas of Compounds

4.2: Names and Formulas of Compounds. Pages 184-201. Names and Formulas of Ionic Compounds. Ionic Compounds: can be represented by: name and/or chemical formula 1. Name: - always a metal (+ ion) followed by non-metal (- ion)

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4.2: Names and Formulas of Compounds

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  1. 4.2: Names and Formulas of Compounds Pages 184-201

  2. Names and Formulas of Ionic Compounds Ionic Compounds: can be represented by: name and/or chemical formula 1. Name: - always a metal (+ ion) followed by non-metal (- ion) - the non-metal ion always ends in the suffix “ide”: Eg: aluminum fluoride 2. Chemical Formula: subscripts indicate the ratio of (+) to (-) ions present in a compound. Eg: AlF3

  3. YOUR TURN!!! Name the following ionic compounds: #1. Li2N Answer: lithium nitride #2. GaI3 Answer: gallium iodide #3. Fe2O3 Answer: iron oxide #4. In what ratio do the atoms of each compound combine?

  4. Writing Formulas of Binary Ionic Compounds • Ionic compounds containing only 2 elements:positive charges balance the negative charges Example: aluminum fluoride Step #1: Identify each ion and its charge: Al3+ F- Step #2: determine total charges needed to balance positive and negative. Al 3+: = +3 F 1- : -1 -1 -1 = - 3 *Charge is balanced when the overall charge equals 0.

  5. Cont’d Step #3: Note the ratio of positive ions to negative ions: 1 Al3+ ion 3 F- ions Step 4: Use subscripts to write the formula: AlF3 *Subscripts must be written in lowest terms.

  6. Compounds Containing a Multivalent Metal • Recall: Multivalent metals can form 2 or more different positive ions. • The periodic table lists the most common ion charge first. Examples: Look at your periodic table. • What are the charges of Nickel, Copper & Manganese? • Which charge is each element most likely found within a compound?

  7. Naming a Multivalent Metal • In order to distinguish between multivalent metals, each ion needs its own specific name. • Roman numerals are used to indicate an ions charge. • I – VII are used to show ion charges 1+ to 7+ • I, II, III, IV, V, VI, VII

  8. How to show the charge when naming a multivalent metal For example look at Ni: Ni can form two different ions: Ni2+ or Ni3+ Therefore in an ionic compound Ni can be written as: nickel (II) or nickel (III) When read aloud, they read as follows: nickel two and nickel three

  9. What Roman Numerals Reveal About an Ion of a Metal 1. Indicates that there is more than one ion for that metal (multivalent). 2. Tells you the exact charge of the metal ion. (See page 189 for examples)

  10. How to Write the Chemical Formula Containing Multivalent Atom Write theformulafor the compound: Chromium (III )bromide: Step 1 - Identify each ion and its charge: chromium (III): Cr3+ Bromide: Br – Step 2 - Determine the total charges needed to balance the charge: Cr3+: = + 3 Br - : -1 -1 -1 = - 3 Step 3 - Note ratio of positive to negative ions: 1 Cr3+ ion for every 3 Br – ions Step 4 – Use subscripts to write formula (a “1” is never shown): CrBr3

  11. Naming a Multivalent Compound What is the name of the following compound? Au3N Step 1 – Identify the Metal: gold (Au) Step 2 – Check the periodic table to see if it is multivalent: YES: Au3+ and Au + Step 3 – Determine the ratio of the ions in the formula: Au3N = 3 gold ions for every 1 nitride ion. Step 4 – Note the charge of the negative ion using the periodic table: N has a charge of 3-

  12. Cont’d Step #5 – (+) and (-) charges must balance. Determine the charge on the metal ion that balances the negative ion: Since we know N has a charge of 3- the Au ion must have a charge of 1+ for it to balance the one N ion with a charge of 3- Thus the name of the gold ion must be gold(I). Step #6 - Write the name of the compound: gold (I) nitride

  13. Polyatomic Ions • An ion composed of more than one type of atom joined by covalent bonds. • Carry an electric charge. • The suffix “ite” and “ate” are used to indicate the presenceandnumber of oxygen atoms. • Rule “ate” polyatomic ions have one more oxygen than “ite” polyatomic ions. • Eg: PO43- : phosphate vs PO33-: phosphite

  14. Writing the Formula for a Polyatomic Ion Write the formula for the following polyatomic ion: manganese (III) chlorate Step #1- identify each ion and its charge: manganese (III): Mn3+ chlorate: ClO3- (refer to Table 4.11, pg 192) Step #2-Balance charges: Mn3+ : = +3 ClO3- : -1 -1 -1 = - 3 Step #3 – Note ratio of positive to negative ions: 1 Mn3+ : = +3 3 ClO3- : -1 -1 -1 = - 3

  15. Cont’d Step #4 – Use brackets around ions to show ratio of ions: (Mn)(ClO3)3 Step #5 – Omit brackets if the value outside the brackets is 1: Mn(ClO3)3

  16. Naming Covalent Compounds Lets review what we know: Ionic Compounds • In ionic compounds subscripts are not used to indicate the actual ratio of ions within a molecule but the smallest whole number ratio. Covalent Compounds • In covalent compounds subscripts are used to show the precise actual number of atoms of each element in the molecule.

  17. Naming Binary Covalent Compounds • Binary Covalent Compound: contains 2 non-metal elements joined together by one or more covalent bonds. Recall: atoms in covalent bonds do not bond by forming ions but rather share electrons. • Binary Covalent compounds can be made up of many atoms: C25H52 or can by diatomic: O2

  18. Naming Covalent Bonds Prefixes and their Meanings: • Indicates the number of atoms present in each element. • Prefixesare ONLYused for binary covalent compounds. • We will first begin by studying prefixes for naming compounds that do not contain H: - See Table 4.13 on pg. 194

  19. For Binary Compounds Not Containing H RULES: #1. Prefix for the 1st element(+ ion) is only shown if it is present more than once: eg. CCl4 #2. Prefix “mono-” is shortened to “mon-” if placed before an oxide (- ion).

  20. Steps to Writing Binary Covalent Compound Names Eg - Write the name of: N2O3 Step #1- Name the element on the left first: nitrogen Step #2 – Name the 2nd element: Oxygen becomesoxide(recall the “ide” ending) Step #3 – Add a prefix to each element: dinitrogentrioxide

  21. Names and Formulas of Covalent Compounds Covalent Compounds: both the name and chemical formula indicates the # or quantity of each type of atom. For Example: dinitrogentrioxide OR N2O3 carbon disulfide OR CS2

  22. Review Rules for Naming Formulas • Page 196

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