Unit 4 Chemical Bonding Why chemical bonds form
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 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: Oxygen 2 - Potassium 1+ Fluorine 1 -
What is the oxidation number for sulfur? 1. 2. 3. 4. 5. 6. 7. 1+ 2+ 3+ 0 123 -
What is the oxidation number for aluminum? 1. 2. 3. 4. 5. 6. 7. 1+ 2+ 3+ 0 123 -
What is the oxidation number for all halogens? 1. 2. 3. 4. 5. 6. 7. 1+ 2+ 3+ 0 123 -
What is the oxidation number for all noble gases? 1. 2. 3. 4. 5. 6. 7. 1+ 2+ 3+ 0 123 -
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 Na. Cl - 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 H 2 • Covalent molecules that like to bond with atoms of the same type N 2 F 2 O 2 I 2 Cl 2 “Have No Fear Of Ice Cold Beverages” Br 2
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 The Atom 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
Identify the type of bonding in the following substance: Fe 1. Ionic 2. Covalent 3. Metallic
Identify the type of bonding in the following substance: Cu. Cl 1. Ionic 2. Covalent 3. Metallic
Identify the type of bonding in the following substance: NO 2 1. Ionic 2. Covalent 3. Metallic
Learning Check • Identify the following as Ionic, Covalent or Metallic • Li. Br • Fe. Cl 3 • CO • Steel Ionic Covalent Metallic Na 3 N Ionic Ca. Br 2 Ionic Cu Metallic NO 2 Covalent
Chemical Formulas – Ionic Compounds • Transition Metal • Iron (III) + Oxygen • Fe 3+ Fe + O 2 - = O = Fe 2 O 3 • 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 – … Fe 3+ and O 2– 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+ Fe + 2 - O+ 3+ Fe = +6 +6 -6 0 2 - O+ 2 - O = -6
Solving Problems 3+ 2 - Fe 2 O 3
Naming Ionic Bonds • Must be - metal + nonmetal • Given Formula – Write the name of 1 st element – Write the name of the 2 nd 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 1 st element, but is on 2 nd – Change the ending of the 2 nd 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 2 nd element (change “ine” to “ide” – Ex: Na. Cl • 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: CH 2 O • Molecular – The actual # of atoms of each element in the compound • Ex: 6 x CH 2 O ---C 6 H 12 O 6 How many carbon atoms? Hydrogen? Oxygen?
Compounds Vs Mixtures • Compounds • Mixtures – Chemical bonds – Just are placed hold the atoms or together ions together – same # of atoms – Can vary or ions – elements – Can Vary proportional
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