Transcript Why Bond?
Compounds and Molecules 4.1 vid What are compounds? Two or more elements chemically combined to form new substances. What are compounds? Chemical Bonds – the attractive forces that hold different atoms or ions together Bonds distinguish compounds from mixtures. Chemical Formula C12H22O11 can only be sugar H20 can only be water Parts to the Formulas 2H2O Coefficient Subscript Parts to the Formulas Coefficient – gives the amount of molecules or moles Subscript – tells the number of atoms or ions Chemical Structure Bond length -the distance between two bonded atoms Bond angle -the angle formed between two bonded atoms Models of compounds Ball and stick model -atoms are represented balls, bonds are represented by sticks. H Bond length Bond Angle O H Models of compounds Structural formulas -chemical symbols represent the atoms. H H O Models of compounds Space-filling -show the space occupied by each atom represented in the Hydrogen compound. Oxygen Structure of Compounds Network Structures = strong solids Molecules= weak solids, liquids, or gases Ionic and Covalent Bonding 4.2 fun Why Bond? Atoms bond so they can become stable! They want to achieve a full outer energy level They want 8 electrons. 1. Ionic bond A bond formed by the attraction between oppositely charge ions. The joining of a positive metal ion and a negative nonmetal ion + Na + Cl NaCl Ionic bond Formed by transferring electrons Now each ion will have 8 valence electrons + Na + Cl NaCl Ionic bond Properties They form network structures high melting points Good conductors of electricity when dissolved or melted because of their ions Metallic bond Formed by the attraction between positively charged metal ions and the electrons around them. Metallic bond Held together by free flowing electrons Hold metallic elements together Covalent Bonds Formed when atoms share one or more valence electrons Formed between non-metals May form single, double, or triple bonds Covalent Properties They are poor conductors of electricity (no ions) Low melting points. form molecules Polyatomic ion An ion made of two or more atoms that are covalently bonded and that act like a single ion. A molecule with a charge -2 Examples: carbonate (CO3) Nitrate (NO3)-1 Fun Compound Names and Formulas 4.3 REMEMBER!!!!!!!! If it starts with metal it is an ionic compound If it starts with a nonmetal it is a covalent compound If the formula contains a parentheses (polyatomic ion) it contains both ionic and covalent bonds If it is just a metal it is metallic Writing Ionic Formulas Calcium Fluoride Step 1 Look up both positive and negative ions 2+ Ca -1 F Writing Ionic Compounds Step 2 Criss-cross numbers down, making subscripts 2+ Ca -1 F Ca1 F2 Writing Ionic Compounds Step 3 Combine your new compound. Ca1 + F2 Ca1F2 Polyatomic ion Aluminum Carbonate +3 Al Al2 -2 ) (CO3 (CO3)3 Al2(CO3)3 Naming Ionic Compounds Step one – Name the first ion in the formula Ex. CaCl2 – calcium Na2(SO4) - sodium Naming Ionic Compounds Step two – Name the second ion Ex. CaCl2 –Calcium Chloride Na2(SO4)-sodium sulfate PROBLEM Ex. Fe2O3 and FeO are different compounds from different ions Fe3+ O2- = Fe2O3 2+ Fe 2O = FeO Solution-Roman Numerals Same naming scheme Add a Roman Numeral to identify the charge of the metal ion. Solution-Roman Numerals Fe2O3 = iron(III)Oxide FeO = iron(II)Oxide Remember!!! R.N. is the charge, not the subscript of the metal. Naming Covalent Compounds Mono – 1 Di - 2 Tri - 3 Tetra - 4 Penta - 5 Hexa – 6 Hepta - 7 Octa - 8 Nona - 9 Deca - 10 Naming Covalent Compounds Step 1 Identify the number of atoms in the first element Ex. H2O two H atoms Naming Covalent Compounds Step 2 Identify the number of nd atoms in the 2 element. Ex. H2O one O atom Naming Covalent Compounds Step 3 Name the compound with the appropriate prefixes. Ex. H2O dihydrogen monoxygen Naming Covalent Compounds Step 4 add an -ide ending to the second element Ex. Dihydrogen monoxide Empirical Formula The simplest chemical formula of a compound. Different covalent compounds can have same empirical formula Ch. 4.4