Ionic Compounds, Names and Formulas

Transcription

1 Bellwork: Elements of the same group are said to have similar chemical properties, why? Answer: Elements in the same group have the same number of valence electrons. Valence electrons are the ones involved in the formation of chemical bonds between two atoms. Chapter 7 Ionic Compounds, Names and Formulas 1

2 What is a chemical bond? The force that holds 2 atoms together. There are two types: 1. Those formed by ions (ionic bond) 2. Those formed by sharing electrons (covalent bonds) What is an ion? An atom with a charge due to a gain or loss of electrons. There are two types: 1. cation positively charged ion, formed when an atom loses one or more valence electrons 2. anion negatively charged ion, formed when an atom gains one or more valence electrons Why do ions form? *To create stability for an atom, remember octet rule. *Elements tend to react in order to have a stable electron structure like noble gases Oxidation Numbers: The charge that is given to an ion once it has gained or lost an electron. Remember the oxidation numbers for main group elements. 1A 2A 3A 4A 5A 6A 7A 8A NOTE: Oxidation numbers are NOT the same as valence electrons. 2

3 Look at Periodic Table. *Think about electron configurations. What configurations make it easier to lose electrons to get to a noble gas? To gain electrons? *What is Ionization Energy? Where will it be easier for an electron to be lost? *When an ion is formed, what happens to the electron configurations???? Cations: Mainly metals, reactive, lose electrons easily. *Groups 1 and 2 are the most reactive and some in group 13. In general, transition metals have an outer energy level of ns 2 because they are filling an inner d sublevel which means most of them will have a 2+ charge. It is possible to lose d electrons so they can form 3+ or greater. Rule of Thumb, 2+ or 3+ (most common) Anions: These are mainly nonmetals, gain electrons needed to form a stable outer shell To distinguish them we add ide to the end of the name. Example: Chlorine, Cl 1 is called a Chloride ion 3

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5 Chemical Formulas *A chemical formula is used to show the atoms present in a specific ratio. *Formula unit the name given for an ionic compound that represents the simplest ratio of the ions involved. *All molecules and compounds have a neutral charge. For example: NH 3 tells us that there is both nitrogen and hydrogen present in the compound. It also tells us that there are 3 Hydrogens needed to cancel out the charge of 1 Nitrogen atom. You already know how to tell how many atoms are in a chemical formula...but let's review. Homework: Complete the Worksheet on Ions, Coefficients, and Subscripts 5

6 In chemical compounds you can have either monatomic ions or polyatomic ions. Monatomic ion a one atom ion such as Mg 2+ or Cl 1 Most of these are easy to pick out using what you already know about the periodic table. Transition metals tend to have more than one monatomic ion aka the list your memorizing Polyatomic ion ions made up of more than one atom BUT they still act as if they were an individual ion in a compound. Its charge applies to the entire group of atoms NEVER change subscripts of the atoms within a polyatomic ion...if more than one is needed use parentheses around the entire ion, with a subscript after. Example: PO 4 3 6

7 Shortcuts for Remembering Polyatomic Ions Oxyanion polyatomic ion composed of an element (usually nonmetal) bonded to one or more oxygen atoms. *Rules for Sulfur & Nitrogen 1. Identify the ion with the greatest number of oxygen atoms. This ion is named using the root of the nonmetal and the suffix ate. 2. Identify the ion with fewer oxygen atoms. This ion is named using the root of the nonmetal and the suffix ite. NO 3 3 NO 2 2 SO 4 2 SO 3 2 Nitrate Nitrite Sulfate Sulfite 7

8 Shortcuts for Remembering Polyatomic Ions *Rules for Chlorine and other Halogens 1. The oxyanion with the greatest number of oxygen atoms is named using the prefix per, the root of the nonmetal, and the suffix ate. 2. The oxyanion with one fewer oxygen atom is named using the root of the nonmetal and the suffix ate. 3. The oxyanion with two fewer oxygen atoms is named using the root of the nonmetal and the suffix ite. 4. The oxyanion with three fewer oxygen atoms is named using the prefix hypo, the root of the nonmetal, and the suffix ite. Ionic Bond The force that holds oppositely charged particles together. It involves the transfer of electrons One atom must gain electrons while the other loses electrons in order to acheive a full octet. Compounds that contain an ionic bond are ionic compounds. Typically involves a metal(+) bonding to a nonmetal( ) Any compound containing a polyatomic ion 8

9 Properties of Ionic Bonds The chemical bonds in a compound determine its properties. Ionic bonds produce unique physical structures, unlike those of other compounds. Ionic compounds do not form single units on a compound but rather form larger compounds with lots of each ion present. 1. Due to the strong attraction between the positive and negative ions, ionic compounds result in solids called crystals. A crystal lattice is a 3 D geometric arrangement of particles, each positive ion is surrounded by negative ions and visa versa. 9

10 Properties of Ionic Bonds 2. Ability to conduct electricity. This is dependent on availability of freely moving ions. a. Solid ionic compounds' ions are locked into fixed positions by strong attractive forces so they do not conduct electricity. b. Ionic compounds in solution or in a liquid state are excellent conductors of electricity. We call these electrolytes. Properties of Ionic Bonds 3. Because ionic bonds are relatively strong, ionic crystals require a lot of energy to be broken. As a result ionic crystals tend to have high melting and boiling points. 4. They are typically hard, rigid, and brittle solids due to the strong attractive forces. 5. Ionic bond formation is always exothermic because bond formation is more stable than the ions that form them. During every chemical reaction energy is either absorbed (endothermic) or released (exothermic). 10

11 Properties of Ionic Bonds 6. They exhibit lattice energy, because of their crystal lattice arrangement, which is the amount of energy required to separate 1 mol of the ions of an ionic compound. The greater the lattice energy the stronger the force of attraction. affected by size of the ions (smaller ions = greater energy affected by the charge of the ion (higher charge = greater energy) Homework: Complete the worksheet on lewis structures and ionic bonding with polyatomic/monatomic ion practice 11

12 Naming and Writing Ionic Compounds Ionic compound names have two parts, just like we have first and last names. Again, the names and naming system used is universal so that scientists around the world can communicate. Overall charge of the formula unit will be zero. The ratio of ions in the formula unit must show that the number of electrons lost by the metal is gained by the nonmetal. Naming Binary Compounds (Ionic) Binary compounds are composed of a positive monatomic ion of a metal and a negative monatomic ion of a nonmetal. Name or write a compound by stating the cation first and the anion second. For monatomic anions the suffix ide is added to the root of the name (Take off the ine, add ide) Examples: CaCl 2 Calcium Chlor ide KF Potassium Fluor ide Na 2 S Sodium Sulf ide Binary Compounds Worksheet 12

13 Naming Polyatomic bonds. Follow the same rules for binary compounds. (Cation has same name as element or of polyatomic ion.) Ending IF polyatomic ion is the name of polyatomic ion. Or use ide if it is an element anion. Polyatomic Ions Worksheet Rules for Naming Ionic Compounds (pg 223) 1. Name the cation followed by the anion. Remember the cation is always written first in the formula. 2. For monatomic cations, use the element name. 3. For monatomic anions, use the root of the element name plus the suffix ide. 4. To distinguish multiple oxidation numbers of the same element, the name of the chemical formula must indicate the oxidation number of the cation. The oxidation number is written as a Roman numeral in parentheses after the name of the cation. Typically applies for transition metals and metals on the right side of the periodic table which often have more than one oxidation number. Example: Fe 2+ and O 2 is Iron(II) oxide 5. When the compound contains a polyatomic ion, simply name the cation followed by the name of the polyatomic ion. Example: NaOH Sodium Hydroxide 13

14 Shortcut to Writing Ionic Bond Formulas. Criss Cross Method. Page 222 #24-26 Page 223 #28-32 Page 979 #3-5 14

15 Worksheets on Ionic Formulas Covalent Bonds formed as a result of sharing electrons. We call the resulting compound a molecule. 15

16 Numerical Prefixes in Covalent Bonds Rules for Naming Binary compounds : note these are composed of two nonmetal atoms not metal atoms or ions. 1. The first element in the formula is always named first, using the entire element name. 2. The second element in the formula is named using its root and adding the suffix ide. 3. Prefixes are used to indicate the number of atoms of each element that are present in the compound. Exceptions: 1.Never use the mono prefix for the first element in the compound. 2. If using a prefix results in two consecutive vowels one is usually dropped to avoid awkward pronunciation. Examples: CO Carbon Monoxide CO 2 Carbon Dioxide CCl 4 Carbon Tetrachloride P 2 O 4 Diphoshorus Tetraoxide Diatomic Molecules A group of nonmetals that are so reactive, because of their desire to have the electron configuration of a noble gas, that they bond with themselves rather than existing as a single atom. You cannot find these elelments in nature by themelves There are seven of them, they form a seven on the periodic table and they start forming the seven at the element seven. N 2, O 2, F 2, Cl 2, Br 2, I 2, H 2 16

17 Common Names *Have you ever had a nice cool refreshing glass of dihydrogen monoxide? *Do you ever put sodium chloride on your vegetables? *Do you ever put sodium hydrogen carbonate into your cookies? Many of these molecular compounds have common names. Some of these common names existed long before this naming system was put into practice. We will always use the chemical names for compounds because they tend to tell us something about the compound. Covalent & Ionic Bonding Practice Worksheet 17

18 Most of the acids we will be concerned about are a special from of ionic copound. If a compound produces hydrogen ions(h + ) in solution it is an acid. In other words, the cation is always H +. Naming Binary Acids OR those without oxygen in the anion They contain hydrogen and one other element. 1.The first word has the prefix hydro to name the hydrogen part of the compound. 2. The acid name comes from the root name of the anion name then add the suffix ic. 3. The second word is always acid. Example: Hydrochloric acid HCl Exceptions: Some acids are named according to the binary acid rule but contain more than two elements. 1. Rule of Thumb: if they do not contain oxygen follow binary acid rules for naming. Example: Hyrocyanic acid HCN Oxyacids acids that contain a hydrogen atom and an oxyanion. Rules of Naming: 1. Acid name comes from the root name of the oxyanion or the central element of the oxyanion. 2. IF the prefix per, or hypo is part of the name of the oxyanion, leave it as part of the name of the acid. 3. Suffixes are based on the ending of the original name of the oxyanion. If the oxyanion's name ends with the suffix ate, replace it with the suffix ic. If the name of the oxyanion ends with the suffix ite, replace it with the suffix ous. 4. The second word is always acid. Examples: HNO 3 Nitric Acid HNO 2 Nitrous Acid 18

19 Naming Organic Molecules Organic contains carbon The alkanes (simplest hydrocarbons) 1. Methane CH 4 2. Ethane C 2 H 6 3. Propane C 3 H 8 4. Butane C 4 H Pentane C 5 H Hexane C 6 H Heptane C 7 H Octane C 8 H Nonane C 9 H Decane C 10 H 22 19

20 Homework on Naming and Writing Acids and Organics. Metallic Bonds Metallic bonds are a unique type of bond that has some properties similar to ionic bonds yet very different too. -Both based on the attraction of particles with unlike charges. -Form crystal lattices in solid state. A metallic bond is the attraction of a metallic cation for delocalized electrons. 1. Metallic bonds are formed due to opposite attracting but in a much more unique way than in ionic or covalent bonds. They form what is called an electron sea model: It is where the electrons distribute themselves around the positive metal ions in the lattice. 2. This sea of frre moving electrons are reffered to as delocalized electrons. 20

21 Compare the electron sea model: If you were asked to walk around and between the desks in the room while staying within the boundaries of the outermost desks you would represent the "sea of electrons" found in a metallic solid and the desks would represent positive ions. You would notice that the number of electrons and the number of cations do not change but the electrons (you) were free to move between the desks (cations). If the desks were put into a long row, you would simply adjust your position and move into a long row with the cations. This is basically what happens in a metallic bond. Metallic Properties * melting and boiling points tend to be high * malleable, ductile, and durable *good conductors *Have luster (shine) due to delocalized electrons interacting with light (photons). *When the # of delocalized electrons increases so does the hardness and strength. Transition metals are generally stronger. 21

22 Alloys A mixture of elements that have metallic properties. This is due to the nature of metallic bond making it easy to introduce other elements into the crystal lattice. Two types: 1. substitutional alloys some atoms of a metal are replaced by other metals' atoms of similar size. 2. interstitial alloys small holes in the lattice structure of a metal are filled with smaller atoms of other metals. They have a wider range of uses than plain metals do due to the unique blend of properties it creates. 22