4.2: NAMES AND FORMULAS OF COMPOUNDS. Pages

Transcription

1 4.2: NAMES AND FORMULAS OF COMPOUNDS Pages

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: AlF 3

3 YOUR TURN!!! Name the following ionic compounds: #1. LN Answer: lithium nitride #2. GaI Answer: gallium iodide #3. Fe 2 O 3 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: Al 3+ F - Step #2: determine total charges needed to balance positive and negative. *Charge is balanced Al 3+: = +3 when the overall F 1- : = - 3 charge equals 0.

5 CONT D Step #3: Note the ratio of positive ions to negative ions: 1 Al 3+ ion 3 F - ions Step 4: Use subscripts to write the formula: AlF 3 *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. A) What are the charges of Nickel, Copper & Manganese? B) 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: Ni 2+ or Ni 3+ 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 the formula for the compound: Chromium (III )bromide: Step 1 - Identify each ion and its charge: chromium (III): Cr 3+ Bromide: Br Step 2 - Determine the total charges needed to balance the charge: Cr 3+ : = + 3 Br - : = - 3 Step 3 - Note ratio of positive to negative ions: 1 Cr 3+ ion for every 3 Br ions Step 4 Use subscripts to write formula (a 1 is never shown): CrBr 3

11 NAMING A MULTIVALENT COMPOUND What is the name of the following compound? Au 3 N Step 1 Identify the Metal: gold (Au) Step 2 Check the periodic table to see if it is multivalent: YES: Au 3+ and Au + Step 3 Determine the ratio of the ions in the formula: Au 3 N = 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 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: dinitrogen trioxide OR N 2 O 3 carbon disulfide OR CS 2

14 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 presence and number of oxygen atoms. Rule ate polyatomic ions have one more oxygen than ite polyatomic ions. Eg: PO 4 3- : phosphate vs PO 3 3- : phosphite

15 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): Mn 3+ chlorate: ClO 3 - (refer to Table 4.11, pg 192) Step #2-Balance charges: Mn 3+ : = +3 ClO 3 - : = - 3 Step #3 Note ratio of positive to negative ions: 1 Mn 3+ : = +3 3 ClO 3 - : = - 3

16 CONT D Step #4 Use brackets around ions to show ratio of ions: (Mn)(ClO 3 ) 3 Step #5 Omit brackets if the value outside the brackets is 1: Mn(ClO 3 ) 3

17 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.

18 NAMING BINARY COVALENT COMPOUNDS Binary Covalent Compound: contains 2 nonmetal 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: C 25 H 52 or can by diatomic: O 2

19 COVALENT BONDING Prefixes and their Meanings: Indicates the number of atoms present in each element. Prefixes are ONLY used 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

20 FOR BINARY COMPOUNDS NOT CONTAINING H RULES: #1. Prefix for the 1st element (metal) is only shown if it is present more than once: eg. CCl 4 #2. Prefix mono- is shortened to mon- if placed before an oxide (non-metal).

21 STEPS TO WRITING BINARY COMPOUNDS Eg - Write the name of: N 2 O 3 Step #1- Name the element on the left first: Nitrogen Step #2 Name the 2 nd element: Oxygen becomes Oxide (recall the ide ending) Step #3 Add a prefix to each element: dinitrogen trioxide

22 REVIEW RULES FOR NAMING FORMULAS Page 196