Intermolecular betweenAttractive forces between molecules Determine phase at room temperature 3 kinds, weakest to strongest: –Dispersion –Dipole-dipole –Hydrogen bonding withinMuch weaker than forces within a molecule.

Intramolecular Force that holds two atoms together Boils down to electrostatic forces –positive nuclei & negative electrons = covalent bonding –positive ion & negative ion = ionic bonding

Energy & Stability Rubberbands Springs Kleenex box Popper High Energy means Low Stability. Low Energy means High Stability.

Stability in Chemical Systems If it exists, it’s stable! Of course, some things are more stable than others.

Noble Gases – What they tell us Group 18 or Group VIIIA or Group O. not stableDo not form compounds under ordinary conditions. They are extremely stable. All have 8 valence electrons: great stability. Must also be low energy!All have 8 valence electrons: great stability. Must also be low energy!

Octet Rule: Why Bonds Form Achieve noble gas electron configurationGoal: Achieve noble gas electron configuration –get 8 valence electrons –except H wants 2 Why: Low energy, high stability stateWhy: Low energy, high stability state HowAtoms form bonds by gaining, losing, or sharing electronsHow: Atoms form bonds by gaining, losing, or sharing electrons

Quick Quiz Elements in the same column have the same ____________________________. number of valence electrons Elements with the same number of valence electrons have similar _____________________________. chemical properties How many valence electrons for column 1 elements? Column 2? Columns ? 12 3,4,5,6,7,8 respectively

3 Types of Bonding IonicIonic: electrons are transferred. CovalentCovalent: electrons are shared. MetallicMetallic: “sea of mobile electrons.”

MetalNonmetal Ionic: Metal + Nonmetal cationMetals: lose valence electrons to attain noble-gas configurations. Get a cation or positive ion. anionNonmetals: gain electrons to complete their valence shells. Get an anion or negative ion.

IONIC BONDING Involves the transfer of electrons.Involves the transfer of electrons. Electrons Lost by Cation = Electrons Gained by AnionElectrons Lost by Cation = Electrons Gained by Anion

Metals are losers! Na has the configuration Ne has the configuration 2-8 If Na loses 1 electron → Na + which has the configuration 2-8-0! takeHas to be something to take the electron.

Na metal 

Nonmetals are winners! Cl has the configuration Ar has the configuration If Cl gains 1 electron → Cl - which has the configuration 2-8-8! donateHas to be something to donate the electron.

Cl 2 (g) 

Electron is transferred from Na to Cl Tiger Graphic Tiger Graphic

Structure of Ionic Compounds Ions are attracted to each other by strong electrostatic interactions. They form a crystal lattice – a regular 3-D pattern or array. Ions are held in fixed positions in the solid state. Unit Cell = smallest repetitive unit in lattice

Good lattice  not too many “dislocations.” NaCl has its own unique properties.

The more Na and Cl 2, the larger the resulting NaCl crystal. Just keep adding on to it.

This crystal was made in a hurry – lots of “dislocations.”

Different representations of a crystal lattice. Properties of Ionic crystals: cleavage movie animation

Lewis Structures of Atoms Symbol + dots for valence electrons Na has 1 valence electron: Cl has 7 valence electrons: Na Cl    

Lewis Structures of Ions Positive ions have no electrons. Negative ions have 8 electrons. Use brackets & right superscript to show CHARGE! Sodium ion is  Na  +1 ::Chloride ion is  :Cl: 

Lewis Diagrams for Ionic Cmpds NaCl has the Lewis structure: [Na] +1 [ Cl ] -1 Lewis Structures for compounds show the valence electrons after the transfer!

Predicting Ionic Compounds What is the ionic compound formed from calcium and iodine?What is the ionic compound formed from calcium and iodine? Calcium is a metal with 2 valence electrons. It loses both  [Ca] +2. Calcium is a metal with 2 valence electrons. It loses both  [Ca] +2. Iodine is a nonmetal with 7 valence electrons. It gains only 1  [ I ] -1. Iodine is a nonmetal with 7 valence electrons. It gains only 1  [ I ] -1. How many iodine ions do you need to make a neutral compound? How many iodine ions do you need to make a neutral compound? 2      

Lewis Diagram of Calcium iodide Ca: goes to Ca +2 : I: goes to I -1 : [Ca] +2 [:I:] -1 [:I:] -1 or [:I:] -1 [Ca] +2 [:I:] -1 Notice that the total charge adds up to zero. Compounds are electrically neutral. ·· ·· ·· ·· ·· ·· ·· ··

Identify Bond Type from Formula Ionic Compounds – SALTS – metal + nonmetal Covalent Compounds – all nonmetals Metallic – all metal

Identifying Ionic Compounds: Metal + Nonmetal CuCl 2 H 2 O KF CO 2 NH 3 CaBr 2 PCl 3 CsI HF Zn(NO 3 ) 2 Na 2 O SiH 4 Al 2 O 3 SO 3 Mn 2 O 3 N 2 O 4 H 2 Se MgOIonic Ionic Ionic Ionic Ionic Ionic Ionic Ionic Ionic Covalent Covalent Covalent Covalent Covalent Covalent Covalent Covalent Covalent

Ionic Compounds The positive & negative ions are attracted to each other by very strong electrostatic forces. Greatly influences properties. In the solid phase, the ions are locked into place. Very hard to pull them apart.

Properties of Ionic Compounds High melting points Low vapor pressures Solids do not conduct electricity Melts (liquid state) do conduct electricity Solutions conduct electricity Tend to be hard and brittle

Aside: What Conducts Electricity? MOBILE CHARGED PARTICLES mobileIf something conducts a current, it has some kind of mobile charged particles: either electrons or ions. If something doesn’t conduct, it doesn’t have particles that are both mobile and charged.

System Universe: Total energy is conserved. Environment Energy can be converted from 1 form to another. Energy can be transferred between the system & the environment. Exothermic Endothermic

A + B  AB reactantsLeft-hand side is starting side. A and B are reactants. productRight-hand side is ending side. AB is product.

Energy & Chemical Bonds Making a bond ReLeases energy! It’s exothermic!

Energy & Chemical Bonds Breaking a bond aBsorbs energy! It’s endothermic!

A + B  AB + energy A bond is formed & energy is released. Product side! AB has less potential energy than A + B. AB is more stable than A + B

AB + energy  A + B A bond is broken & energy is absorbed. The energy term is on the reactant side! The products are higher in energy than AB, the reactant.

Stability vs. Energy endothermicIn an endothermic process, energy is absorbed. System goes from low to high energy. So stability goes down. exothermicIn an exothermic process, energy is released. System goes from high to low energy. So stability goes up.

The greater the energy released when the bond is formed, the more stable the bond. RXN 1 B + C  BC Joules RXN 2 K + L  KL Joules Which product is more stable, BC or KL?

Equations for Ionic Bonding Na 0  Na e - Cl 0 + 1e -  Cl - A single electron transferred from the Na to the Cl

Cl 2 is diatomic In the equation, you have to write Cl 2 because that’s the form of the reactant.

2Na(s) + Cl 2 (g)  2NaCl(s) Since you have 2 Cl, you need 2 Na. Hopefully you know that for this reaction, THE REACTANTS FORM PRODUCT If a product is formed, it’s more stable than the reactants. If it’s more stable, it has less energy.

Movie Movies on Ionic Bonding Movie 1 on formation of NaCl Movie 2 on formation of NaCl Movie 3 on formation of AlBr 3Movie 3 on formation of AlBr 3

COVALENT BONDING The electrons are shared, not transferred. ElementsElements: Covalent bonds can form between nonmetal atoms of the same element. –H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2 CompoundsCompounds: can form between nonmetal elements of different elements. –HCl, NO 2, CO, PH 3, H 2 Te

METALLIC BONDING Metals form the strongest solids and have unique properties. valence electrons Put a bunch of metal atoms together – the valence electrons lose sense of belonging to any specific nucleus. Kernels or +’ve nuclei are packed close together in a crystal lattice; valence electrons move throughout.

Movie Movie on formulas, ball-and-stick models, space-filling models