Intermolecular Attractive forces between molecules Determine phase at
Intermolecular • Attractive forces between molecules • Determine phase at room temperature • 3 kinds, weakest to strongest: – Dispersion – Dipole-dipole – Hydrogen bonding • Much 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. • Do not form compounds under ordinary conditions. They are extremely stable • All have 8 valence electrons: great stability. Must also be low energy!
Octet Rule: Why Bonds Form • Goal: Achieve noble gas electron configuration – get 8 valence electrons – except H wants 2 • Why: Low energy, high stability state • How: How 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 1318? 1 2 3, 4, 5, 6, 7, 8 respectively
3 Types of Bonding • Ionic: Ionic electrons are transferred. • Covalent: Covalent electrons are shared. • Metallic: Metallic “sea of mobile electrons. ”
Ionic: Metal + Nonmetal • Metals: lose valence electrons to attain noble-gas configurations. Get a cation or positive ion. • Nonmetals: gain electrons to complete their valence shells. Get an anion or negative ion.
IONIC BONDING • Involves the transfer of electrons. • Electrons Lost by Cation = Electrons Gained by Anion
Metals are losers! • Na has the configuration 2 -8 -1 • Ne has the configuration 2 -8 • If Na loses 1 electron → Na+ which has the configuration 2 -8 -0! • Has to be something to take the electron.
Na metal
Nonmetals are winners! • Cl has the configuration 2 -8 -7 • Ar has the configuration 2 -8 -8 • If Cl gains 1 electron → Cl- which has the configuration 2 -8 -8! • Has to be something to donate the electron.
Cl 2 (g)
Electron is transferred from Na to Cl 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
Na. Cl has its own unique properties. Good lattice not too many “dislocations. ”
The more Na and Cl 2, the larger the resulting Na. Cl crystal. Just keep adding on to it.
This crystal was made in a hurry – lots of “dislocations. ”
Properties of Ionic crystals: cleavage movie animation Different representations of a crystal lattice.
Lewis Structures of Atoms • Symbol + dots for valence electrons Na • • Cl has 7 valence electrons: Cl • Na has 1 valence electron:
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. . -1 • Chloride ion is : Cl : . .
Lewis Diagrams for Ionic Cmpds Na. Cl has the Lewis structure: • • -1 +1 [Na] [ • Cl • ] • • Lewis Structures for compounds show the valence electrons after the transfer!
Predicting Ionic Compounds • What is the ionic compound formed from calcium and iodine? • Calcium is a metal with 2 valence electrons. It loses both [Ca]+2. • Iodine is a nonmetal with 7 valence -1 electrons. It gains only 1 [ I ]. • How many iodine ions do you need to make a neutral compound? 2
Lewis Diagram of Calcium iodide Ca: 2 -8 -8 -2 goes to Ca+2: 2 -8 -8 -0 I: 2 -8 -18 -18 -7 goes to I-1: 2 -8 -18 -18 -8 ·· ·· ·· -1 +2 or [: I: ] [Ca] [: I: ] · ·· · Notice that the total charge adds up to zero. Compounds are electrically neutral. ·· -1 +2 [Ca] [: I: ]
Identify Bond Type from Formula • Ionic Compounds – SALTS – metal + nonmetal • Covalent Compounds – all nonmetals • Metallic – all metal
Identifying Ionic Compounds: Metal + Nonmetal • • • Cu. Cl 2 Ionic H 2 O Covalent KF Ionic CO 2 Covalent NH 3 Covalent Ca. Br 2 Ionic PCl 3 Covalent Cs. I Ionic Covalent HF • • • Zn(NO 3)2 Ionic Na 2 O Ionic Si. H 4 Covalent Al 2 O 3 Ionic SO 3 Covalent Mn 2 O 3 Ionic N 2 O 4 Covalent H 2 Se Covalent Mg. O Ionic
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 • If 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.
Universe: Total energy is conserved. Energy can be Exothermic converted from 1 form to another. System Environment Endothermic Energy can be transferred between the system & the environment.
A + B AB • Left-hand side is starting side. A and B are reactants • Right-hand side is ending side. AB is product
Energy & Chemical Bonds Making a bond Re. Leases energy! It’s exothermic!
Energy & Chemical Bonds Breaking a bond a. Bsorbs 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 • In an endothermic process, energy is absorbed. System goes from low to high energy. So stability goes down. • In 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 + 100 Joules RXN 2 K + L KL + 400 Joules Which product is more stable, BC or KL?
Equations for Ionic Bonding Na 0 Na+1 + 1 e. Cl 0 + 1 e- 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.
2 Na(s) + Cl 2(g) 2 Na. Cl(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 Na. Cl • Movie 2 on formation of Na. Cl • Movie 3 on formation of Al. Br 3
COVALENT BONDING • The electrons are shared, not transferred. • Elements: Elements 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 • Compounds: Compounds 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. 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
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