Unit 7: Bonding NaCl N2N2

Overview Chemical bonds provide the glue that hold compounds together… In this unit you will learn:  The different types of bonds and how to identify them.  How electrons are used in bonding.  How to draw models of compounds with different types of chemical bonds.

Any time a bond is formed or broken a chemical change occurs Atoms form bonds because they are unstable By trading or sharing electrons atoms can stabilize (becoming like Noble Gases) The only electrons that can be used in bonding must come from the outer most shell of electrons (Valence Electrons) Basics of Bonding

When something is “stable” it usually has low energy Because bonds are formed as a way of stabilizing an atom:  When a bond is broken energy increases ~ Endothermic  When a bond is formed energy decreases ~ Exothermic The more energy released when a bond is formed then the stronger the bond is… Energy of Bonding Vs.

8 valence electrons = Stable Atom For smaller atoms 2 electrons is enough to fill the valence shell (H, Li, Be, and B follow “Duet” Rule) The Octet Rule Octet Rule – most atoms tend to gain, lose, or share electrons to have 8 valence electrons C would like to N would like to O would like to Gain 4 e- Gain 3 e- Gain 2 e- Review Lewis Dot Diagram Pre-lesson…

Lewis Dot Diagram (Review) Draw Electron dot diagrams for the following: Sodium atomPotassium ion Magnesium atomCalcium ion Chlorine atomIodide ion Aluminum atom

The following types of chemical bonds are formed in an effort to fill electron shells:  Ionic Bonds  Covalent Bonds  Metallic Bonds  Hydrogen Bonds Types of chemical bonds Intermolecular Forces Intramolecular Forces Intramolecular – bonds between atoms to form compounds Intermolecular – bonds between separate molecules that hold particles together (like solids)

A bond formed between metal and nonmetal ions by transferring electrons Metals lose e - & Non-Metals gain e - to satisfy “octet rule” Weak Bond = Weak Intramolecular Force High Melting Point = Strong Intermolecular Force Other Properties: Conducts Electricity when dissolved in water Arrange themselves in crystal formation Ionic Bonds Difference in electronegativity of 1.7 or greater

Drawing Lewis Dot Diagrams to show this: Ex) KBr Ex) MgO Ex) CaCl 2 Ex) Al 2 O 3 Ionic Bonds Pt. 2 This Animation shows how ionic bonding works between atoms

Bond formed when nonmetal atoms share valence electrons to satisfy the “octet rule” Electrons are shared in pairs:  Single bond = 2 electrons shared  Double bond = 4 electrons shared  Triple bond – 6 electrons shared Strong Bond = Strong Intramolecular Force Low Melting Point = Weak Intermolecular Force Other Properties: Poor Conductors, form Molecular Compounds Covalent Bonds

To draw Lewis dot diagrams for covalent bonds follow these guidelines: o These are 5 easy steps to follow for drawing simple Lewis dot diagrams. Covalent Bonds Pt. 2

Try to draw Lewis Dot Diagrams for the following compounds: Ex) Cl 2 Ex) H 2 O Ex) CO 2 Ex) PCl 3 Covalent Bonds Practice

Answers: *Remember one bond per side

Remember bonds between any two nonmetal atoms will be covalent. So…Diatomic Molecules and Polyatomic Ions both have covalent bonding. Covalent Bonds Pt. 3 The Diatomic Elements: sharing of e- between two of same atom Br 2 I 2 N 2 Cl 2 H 2 O 2 F 2 SO 4 -2 NO 3 - These may have ionic charges, but share electrons between non-metal atoms

The 2 types of covalent bonds are: Covalent Bond Types Non-PolarPolar - Equal Sharing of electrons - Same Electronegativities - Symmetrical molecules - Won’t dissolve in water - Unequal Sharing of electrons - Has difference in electronegativity less than 1.7 (Ionic bonds > 1.7) - Asymmetrical molecules -Can dissolve in water because water is polar, and “likes dissolve likes”

Non-Polar Vs. Polar Covalent Bond Types Polar molecules have a dipole moment because all of the electrons are pulled in the direction of the most electronegative element makes them asymmetrical (uneven shaped)

Non-Polar Vs. Polar Covalent Bond Types

For Covalent/Molecular compounds IMF = Inter- Molecular Forces hold particles together… Dipole-Dipole Attractions – for ionic compounds and polar covalent compounds, because the molecules have positive and negative sides nearby molecules are attracted to each other Hydrogen Bonding – The strongest IMF, where a hydrogen atom in one molecule is attracted to the most electronegative element in another molecule “Physical” Bonds “IMF”

This is NOT a chemical bond between hydrogen and another atom in a compound. It is a physical attraction between a Hydrogen atom in one molecule usually to a Nitrogen or Oxygen atom in another molecule. Causes water to expand when it freezes Allows for surface tension in water Hydrogen Bonding

We only have 2: 1) Covalent bonds (between nonmetals) 2) Ionic bonds (between metals + nonmetals) So in a compound like this: - It has both types of bonds, but it is an ionic compound. Chemical Bond Types With a polyatomic ion

Metallic Bonding - Bond found in metals; holds metal atoms together strongly - Metal atoms mix together held in place by a “sea” of mobile electrons - Good conductors with very high melting points -Malleable -Ductile

Metallic Bonds Pt. 2

Metals do not chemically combine with metals. They form alloys which is a solution of a metal in a metal. Examples including: steel, brass, bronze and pewter, most gold jewelry. Metallic Bonds Pt. 3

Low melting and boiling point = weak IMF Bond strength: Covalent > Metallic > Ionic Properties of Bond Types: Bond Type MP & BP Hardness Conductivity Solid State Liquid State Aqueous MetallicHigh (except Hg) HardYes IonicHighHardNoYes CovalentLowSoftNo

Determining the shape of a molecule will help us decide whether a compound is polar vs. non- polar VSEPR Theory – is a theory used in chemistry to predict the geometry of molecules depending on how many electron pairs are found around the central atom It is important to know what a lone pair of electrons is on a central atom… Shapes of Molecules: Valence Shell Electron Pair Repulsion

VSEPR Theory: Number of bonds/lone pair e-ShapeExamples 1 bond or 2 bonds only (with 0 lone pairs) linear N 2, CO 2, HCl 2 bonds with 2 lone pairsbent H 2 O, SO 2 3 bonds with 0 lone pairsTrigonal Planar BH 3, SO 3 3 bonds and 1 lone pairTrigonal Pyramidal NH 3, PCl 3 4 bonds with 0 lone pairsTetrahedral CH 4, SiCl 4 5 bonds with 0 lone pairsTrigonal Bipyramidal PCl 5 6 bonds with 0 lone pairsOctahedral SF 6 **Lone pairs must be on center atom to change geometry

Linear

Bent

Trigonal Planar:

Trigonal Pyramidal

Tetrahedral

Trigonal Bipyramidal

Octahedral

Lastly… Ionic Molecules Repeating particles in crystals are ions (+/- ) Dipole attractions. Examples: NaCl, KNO 3, CaCl 2, etc.