Ionic Compounds: Compounds that are made of oppositely charged ions.

Forming Ionic Compounds  Elements can combine to make ionic compounds when their atoms lose or gain electrons.  Any atom that has gained or lost electron(s) is called an ion and is now charged.  When atoms gain an electron, they are more negative (electrons are negatively charged particles) and are called anions.  When atoms lose an electron, they are more positive and are called cations.  Ionic compounds are when an anion and a cation come together to form a neutral compound, which is more stable.

 The loss and gain of electrons is what makes a full outer energy level.  Remember, we only need to look at the outer energy level. These electrons are called valence electrons.  Ionic compounds are usually composed of one metal (left side of periodic table) and one non-metal (right side).  E.g. How many valence electrons does Lithium have? Do you think it will gain or lose it’s electron(s)? Why?  Answer:  It has 1 valence electron. It will lose it’s electron when forming an ion because it is easier to lose one than gain 7 in order to have it’s last energy level filled up.

Naming Binary Ionic Compounds  There are two ways to identify a compound:  By its chemical name  By its chemical formula  These are the IUPAC rules for naming:  1. The 1st part always identifies the positive ion (metal cation)‏  2. The 2nd part always identifies the negative ion (non-metal anion)‏

Examples:  Magnesium and phosphorus make magnesium phosphide.  Sodium and chlorine make:  Sodium chloride  Calcium and bromine make:  Calcium bromide

Examples:  Write the names of the following binary ionic compounds:  MgBr 2 CaI 2 Al 2 O 3 KCl  Magnesium bromide  calcium iodide,  aluminum oxide,  potassium chloride.

Activity: 4-2  Text: p  Use hole punches as valence electrons  Step 1: Find metal on periodic table and write the symbol.  Step 2: Figure out how many valence electrons it has (hint: look at the column number it is in)‏  Step 3: record the number of valence electrons  Step 4: Find non metal and write the symbol  Step 5: Figure out how many valence electrons it has  Step 6: record the number of valence electrons  Step 7: Give the metal’s electrons to the non-metal  Step 8: You may have to add extra metals or non-metals in order to fill the valence shell.

Writing the Chemical Formula  You won’t always be able to use cut outs, so follow these steps for a faster way of determining the chemical formula:  Step 1: identify each ion and its charge  Step 2: Determine the total positive charge and total negative charge needed to equal zero.  Step 3: Note the ratio of cations to anions  Step 4: Use subscripts to show the ratio of ions.

Examples:  Aluminum Fluoride:  1. Aluminum: Al 3+ Fluoride: F -  2. Al 3+ = 3+ F - = (-1) x 3 = 3-  3. 1 Al 3+ : 3 F -  4. AlF 3

Examples:  Try magnesium Nitride:  Try page 146 #6-8

Multivalent Metals  Some metals have more than one ion charge listed in the periodic table. These elements are called multivalent metals  Eg. Copper: can be a 1+ or 2+ charge.  To distinguish between the two, we use Roman Numerals after the element name.  Eg. Cu +1 is written Copper(I) and Cu +2 is written Copper(II)

Chemical Formula for Multivalent Metals  Example: SnS 2  Step 1: Identify the metal  Sn (tin)‏  Step 2: Verify that the metal can form more than one kind of ion  Sn 2+ and Sn 4+  Step 3: Determine the ratio of ions in the chem formula  1 tin : 2 sulfide  Step 4: Note the charge of the anion  2-

 Step 5: The positive and negative charges must balance out so the net charge is zero.  Total neg. charge: 4-  Total pos. charge: 4+  Step 6: Determine what charge the metal ion must have to balance the anion.  1 Sn? = 4+  Step 7: Write the name of the metal ion  The name of the metal ion is tin(IV)‏  Step 8: Write the name of the compound  Tin (IV) sulfide

Examples:  Cu 3 N  Answer:  Copper (I) nitride

Polyatomic Ions  A polyatomic ion is an ion made up of more than one atom  Poly = many  These ions usually end in -ate.  Examples: Ammonium: NH 4 +  Phosphate: PO 4 3-  Carbonate: CO 3 2-  Sulfate: SO 4 2-  Hydroxide: OH -  Nitrate: NO 3 -

Chemical Formula with Polyatomic Ions  Example: Aluminum carbonate  Step 1: Use the periodic table and a talbe of common polyatomic ions to identify each ion and its charge:  Aluminum: Al 3+  Carbonate: CO 3 2-  Step 2: Determine the total positive charge and total negative charge to equal zero.  Al 3+ = 2 (3+) = 6+  CO 3 2- = 3(2-) = 6-  (6+) + (6-) = 0

 Step 3: Note the ratios of cations to anions:  2:3  Step 4: Use the subscripts to show the ratio of ions. Place the polyatomic ion in brackets if it needs a subscript.  Al 2 (CO 3 ) 3  Now, you try: Ammonium sulfate  Answer:  (NH 4 ) 2 SO 4 Now work on questions on page 150 #9 and 10 Page 151 # 1-8

Molecular Compounds  It is a compound formed when atoms of 2 or more different elements share electrons.  They are similar to ionic compounds, but instead of one element giving it’s electrons to the other, they share the electrons between the two atoms.  The shared electrons form a covalent bond.  Molecules can be formed by two or more of the same element OR two or more of different elements.  E.g. Oxygen found in the atmosphere is O 2  Oxygen is not a compound, since it contains only one type of atom.

Activity 4-3  Use p. 154 in your text to follow the directions for activity 4-3

Naming Binary Molecular Compounds  E.G. carbon dioxide  Tells us 2 pieces of info:  Compound is composed of carbon and oxygen  Tells you the ratio of the two elements  Carbon: 1  Oxygen: 2 (di)‏  “di” is a prefix that tells you the number of atoms in that element.

Prefixes 8octa4tetra 7hepta3tri 6hexa2di 5penta1mono

Using the Prefixes  Smog has a lot of molecular compounds in it, nitrogen dioxide is an example.  Use the four steps to name binary molecular compounds…

 Step 1: Count the # of atoms of the first element in the chemical formula  Example: N 2 O 4  # of nitrogen: 2  Step 2: Write the appropriate prefix followed by the name of the element. (mono- is never used if it is the first name in the molecule)‏  Dinitrogen  Step 3: Count the # of atoms in the second element  # of Oxygen:4  Step 4: Write the prefix and the element and finally the suffix (-ide)‏  Tetroxide  Final name: dinitrogen tetroxide

You try it!  BrCl (used to detect mercury in water)‏  Answer:  Bromine monochloride  Try page 156 #1-4

Writing Chemical Formulas for Binary Molecular Compounds  Step 1: Write the chemical symbol of 1st element  Example: phosphorus trichloride PP  Step 2: Determine the number of atoms in 1st element  # of P: 1  Step 3: Write chem. Symbol of 2nd element  Cl  Step 4: Determine # of atoms in 2nd element  # of Cl: 3  Write formula:  PCl 3

Try These:  P. 158 #3, 6.