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Unit 4 Chemical Bonding Why chemical bonds form? • It takes energy to separate atoms that are bonded together. • The same energy is released when chemical bonds form. • Atoms form bonds to reach a lower energy state. A chemical bond forms when atoms transfer or share valence electrons. Valence electron are what get transferred or shared to form the chemical bond Forming Chemical • Octet Rule Atoms will form Bonds bonds by: – Sharing – Giving or – Taking electrons to complete their octet Or be like a Noble Gas Higher energy farther away from nucleus Forming Chemical Bonds • Lithium –Better to lose 1 electron or to gain 7 electrons? X Ionization • Neutral element: # protons = # electrons -wants to lose an e’ Na 1+ - wants to gain an e’ Cl 1- OXIDATION #s Oxidation Numbers - indicate # of e’ lost or gained PRACTICE: 2 Oxygen + 1 1 Potassium Fluorine What is the oxidation number for sulfur? 1+ 2+ 3+ 0 1230% 3- 0% 2- 0% 1- 0% 0 0% 3+ 0% 2+ 0% 1+ 1. 2. 3. 4. 5. 6. 7. What is the oxidation number for aluminum? 1+ 2+ 3+ 0 1230% 3- 0% 2- 0% 1- 0% 0 0% 3+ 0% 2+ 0% 1+ 1. 2. 3. 4. 5. 6. 7. What is the oxidation number for all halogens? 1+ 2+ 3+ 0 1230% 3- 0% 2- 0% 1- 0% 0 0% 3+ 0% 2+ 0% 1+ 1. 2. 3. 4. 5. 6. 7. What is the oxidation number for all noble gases? 1+ 2+ 3+ 0 1230% 3- 0% 2- 0% 1- 0% 0 0% 3+ 0% 2+ 0% 1+ 1. 2. 3. 4. 5. 6. 7. PRACTICE • Mg • Fe (III) • Cl •S • Be + 2 + 3 1 – 2 + 2 – • Cu (II) • Br • Na • Cu (I) •N + 2 1 1 + 1 _ 3 + Ionic Bonds NaCl - salt + • Forms between a metal and nonmetal • Atoms LOSE or GAIN its valence electrons • ve’ are transferred from one element to another Covalent Bond • Forms between 2 nonmetals • Atoms SHARE electrons – H wants to give an e’ – O wants to take 2 e’ – SHARE between – highest energy level. DIATOMIC MOLECULES H2 • Covalent molecules that like to bond with atoms of the same type N2 F2 O2 I2 Cl2 “Have No Fear Of Ice Cold Beverages” Br2 Ionic Covalent • Gain / Lose e’ • 2 opposite charged ions • Bonds between metals and nonmetals • Compound •Share e’ •2 same charged elements •Bonds between 2 nonmetals •Molecules Why do Atoms form Bonds? Are most atoms stable? Electronegativity • Electron pairs in covalent bonds may be shared unequally. – Strong electronegativity pulls the e’ more towards one atom – Group 17 (VII) strong electronegativity – Group 1 (I) weak electronegativity Copper Atom Cu Cu Cu Cu Cu Cu Cu Cu Cu Cu Cu Cu Cu The Atom Cu Cu Cu Cu Cu Cu Cu Cu Cu Cu Cu Cu Cu Cu Cu Cu C Cu Cu Cu C Cu Metallic Bond • Formed between atoms of metallic elements • Electron cloud around atoms • Good conductors at all states, lustrous, very high melting points • Examples; Fe, Al, Au, Co Metallic Bond A Sea of Electrons Metals Form Alloys Metals do not combine with metals. They form alloys. - which is a solution of a metal in a metal Examples: steel, brass, bronze and pewter. Identify the type of bonding in the following substance: KBr 1. Ionic 2. Covalent 3. Metallic lic 0% M et al en t 0% Co va l Io ni c 0% Identify the type of bonding in the following substance: Fe 1. Ionic 2. Covalent 3. Metallic lic 0% M et al en t 0% Co va l Io ni c 0% Identify the type of bonding in the following substance: CuCl 1. Ionic 2. Covalent 3. Metallic lic 0% M et al en t 0% Co va l Io ni c 0% Identify the type of bonding in the following substance: NO2 1. Ionic 2. Covalent 3. Metallic lic 0% M et al en t 0% Co va l Io ni c 0% Learning Check • Identify the following as Ionic, Covalent or Metallic • LiBr • FeCl3 • CO • Steel Ionic Ionic Covalent Metallic Na3N Ionic CaBr2 Ionic Cu Metallic NO2 Covalent Chemical Formulas – Ionic Compounds • Transition Metal • Iron (III) + Oxygen • Fe 3+ Fe O 2- = + O = Fe2 O3 • Criss-cross the oxidation #s not the + or- signs Solving Problems • Iron and oxygen combine to form a compound. Iron (Fe) has an oxidation number of 3+. Oxygen (O) has an oxidation number of 2–. • Predict the chemical formula of this compound. Solving Problems 1. Looking for: – …formula for a binary compound 2. Given – … Fe3+ and O2– 3. Relationships: – Write the subscripts so that the sum of the oxidation numbers equals zero. 4. Solution – – Two iron atoms = 2 × (3+) = 6+ Three oxygen atoms = 3 × (2–) = 6– Solving Problems 3+ Fe 3 x 2- O 2 = 6 Solving Problems 3+ 2- Fe O+ + O+ 3+ Fe = +6 2- +6 -6 0 2- O = -6 Solving Problems 3+ 2- Fe2 O 3 Naming Ionic Bonds • Must be - metal + nonmetal • Given Formula – Write the name of 1st element – Write the name of the 2nd element – but change end to “ide”. • Given Name – Write the Ox #’s above each element – Write the chemical symbol of each element – Criss-Cross the oxidation numbers Naming Covalent Bonds • Must be - nonmetal + nonmetal • Given Formula – Look at the subscript for each element – Use the Greek prefix to show the # • “mono not necessary on 1st element, but is on 2nd – Change the ending of the 2nd element to “ide” • Given Name – Use the Greek prefixes to determine the subscripts for each element. – Write the chemical symbol then subscript. Naming Ionic Compounds • Simple Ionic – Name first element – Root name of 2nd element (change “ine” to “ide” – Ex: NaCl • Sodium + chlorine • = sodium chloride Naming Covalent Compounds • • • • • • Prefix AKA molecular monocompounds di Binary Compounds – tri have only 2 elements tetra Name the + ion penta Name the – ion (change “ine” to “ide” AND give the hexa # of atoms hepta Ex: CO – carbon monoxide octa nona - Meaning 1 2 3 4 5 6 7 8 9 Formulas • Empirical – Simplest whole # ratios by which the elements combine • Ex: CH2O • Molecular – The actual # of atoms of each element in the compound • Ex: 6 x CH2O ---C6H12O6 How many carbon atoms? Hydrogen? Oxygen? Compounds Vs Mixtures • Compounds • Mixtures – Chemical bonds – Just are placed hold the atoms together or ions together – same # of atoms – Can vary or ions – elements – Can Vary proportional