Chemical Bonding Unit 4

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.

Valence electron are what get transferred or shared to form the chemical bond A chemical bond forms when atoms transfer or share valence electrons.

Forming Chemical Bonds 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: OxygenPotassium Fluorine

What is the oxidation number for sulfur?

What is the oxidation number for aluminum?

What is the oxidation number for all halogens?

What is the oxidation number for all noble gases?

PRACTICE Mg Fe (III) C l S Be – 2 – 2 + Cu (II) Br Na Cu (I) N _

Ionic Bonds Forms between a metal and nonmetal Atoms LOSE or GAIN its valence electrons ve’ are transferred from one element to another + NaCl - salt

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 Covalent molecules that like to bond with atoms of the same type “Have No Fear Of Ice Cold Beverages” H 2 N 2 F 2 O 2 I 2 Cl 2 Br 2

Ionic Covalent Gain / Losee’ 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 Copper Atom

Cu The Atom

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: CuCl 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 LiBrNa 3 N FeCl 3 CaBr 2 COCu SteelNO 2 Ionic Covalent Metallic Ionic Metallic Covalent

Chemical Formulas – Ionic Compounds Transition Metal Iron (III) + Oxygen Fe 3+ +O 2- = Fe 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.

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

Fe 3+ O 2- 32x=6 Solving Problems

Fe 3+ + =+6 Fe 3+ O 2- + O + O = Solving Problems

Fe 3+ O Solving Problems

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: NaCl Sodium + chlorine = sodium chloride

Naming Covalent Compounds AKA molecular compounds Binary Compounds – have only 2 elements Name the + ion Name the – ion (change “ine” to “ide” AND give the # of atoms Ex: CO – carbon monoxide Prefix Meaning  mono-1  di - 2  tri -3  tetra - 4  penta - 5  hexa - 6  hepta7  octa8  nona - 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 –Chemical bonds hold the atoms or ions together –same # of atoms or ions –elements proportional Mixtures –Just are placed together –Can vary –Can Vary