Ch. 7 and 8 BondingCh. 7 and 8 Bonding

Valence Electrons = electrons found in the last occupied shell of an atom (their “changeable” electrons in their last shell)

KC3 = It is the same as the “A” group number

Lewis Dot Structures = shorthand representations of the chemical symbol and the valence electrons

lose 1 lose 2 lose 3 gain 4 gain 3 gain 2 gain 1 no change lose 4

+1 +2 +3 +- 4 -3 -2 -1 0

KC 4 = Metals tend to lose electrons and non-metals tend to gainKC 5 = Losing electrons, usually a metal

Na Na+ + e-

Pseudo Noble Gas = when an atom gains or loses electrons until they have a full/stable octet (8). They “behave” like a noble gas.

KC 6 = Anions form by gaining electrons, usually a non-metal

Cl + e- Cl-

Halide ion = at atom from the halogen group that has gained an electron and become an anion (negative ion)

Section 7.2Section 7.2Ionic Compound - a compound formed from the bonding of a cation and an anionKC 14 = Electrically neutral, the positive cation and the negative anion cancel each other outIonic Bond - the electrostatic bond that holds ions together (the “magnetic” attraction that pulls + and - together)

Chemical Formula - shows the kinds and numbers of atoms in the smallest representative unit of that substance

Formula Unit - one “functional piece” of that substance in lowest whole number ratio

Magnesium and Chlorine? F? Ca and Cl?

Aluminum and Bromine?Na and O?Na and N?Ca and O?Ca and N?Al and S?Al and N?

The atoms react to cancel out their charges.

Ionic PropertiesMetal and a Nonmetal

Neutral Charge

Strong Intermolecular Attraction

Solid Crystalline Lattice

High Melting/Boiling Points

Liquid form conducts Electricity

Coordination Numbers

Cesium Chloride

Formula Unit - the lowest ratio of atoms in an ionic compound = “one piece”

Jump to Chapter 8Skip Ch. 7.3

Covalent Bonding Covalent Bonding Ch. 8Ch. 8Covalent Bond = An equal SHARING of valence electrons usually between two or more nonmetals. (A tug of war between two elements trying to gain electrons)Molecule = a particle joined together by covalent bonds and has no net chargeMolecular compound - composed of moleculesDiatomic - two atoms covalently bonded

Molecule vs. Formula UnitA molecule can exist as a single entity (one piece of a gas). An ionic compound cannot they are called “network” solids. Therefore it isn’t an individual molecule its called a formula unitKC 1 = Molecular Compounds or Covalent Bonds usually have low melting and boiling points (already gases and liquids)

Compare and Contrast Ionic and Covalent/Molecular Properties

Skip to Ch. 8.4

Nonpolar Covalent - electrons shared equally

Polar Covalent - electrons shared, but unequally

KC 32 = The more electronegative (greedy)atom attracts electrons more strongly and therefore gains a slight negative charge, the less electronegative atom gains a slight positive charge

Use the chart to the right to calculate the difference beteween the electronegativity values and determine the bond type.

F = 4.0 Li = 1.0

4.0 - 1.0 = 3.0 Ionic

Ionic vs Polar vs Covalent

Covalent (O2 gas) Polar (H2O) Ionic (NaCl)

Share electrons equally Unequal Exchange

Gas/Liquid Liquid Solid

Low MP and BP Moderate High MP + BP

No conducting Electricity Poor Good Conductor

Polar

Carbon + Hydrogen

Unequal share

Moderate MP and BP

Liquids and Gases

Moderate Bonds

Poor Conductivity

Poor to moderate

Some overlap

Go back to Ch. 7.3 Metallic Bonding

KC23 = As a “sea” of mobile valence electronseach metal atom wants to lose, so therefore they just pass the electrons around between atoms

Metallic Bond = The attraction of the free-floating valence electrons for the positively charged metal ions

Mobile electrons result in metals that are shiny and good conductors of heat and electricity, and the lack of permanent/consistent bonds means they are malleable and ductile

Contrasted with Ionic bonds which are not malleable because the bonds are more permanent, and therefore not malleable, likely to break when struck

KC 24 = very compact and orderly, similar to a ionic crystals

Alloy = a homogenous mixture of 2 or more metals

KC 25 = the properties of alloys are often superior to the component elementsSterling silver (Ag and Cu) Cast Iron (Fe C)

Brass (Cu Zn) Bronze (Cu Sn)

Stone Age = Flint tools and weapons, Gold discovered, but too soft, not a good tool/weapon

Copper Age = decent tool/weapon (3800BC Melting Ores, Cu melting temp relatively low 1083C)

Bronze Age = 2800BC natural alloys of copper and tin, unbelievably useful, weapons and tools, but mostly for ruling class and armies, powerful civilizations

Iron Age - 1500BC Iron abundant but relatively high melting point (1500C) makes hard to work with in primitive forge, literally hammer out impurities, and reforge (but still not better than Bronze)

Steel Age - 1100BC heating iron in a forge with Charcoal (carbon)

then water quenching = Steel China is melting and casting Iron by 500BC, and this isn’t done in Europe until 1100AD. Wow!!

Electrochemical cell = a device capable of either deriving electrical energy from chemical reactions, or facilitating chemical reactions through the introduction of electrical energy.

A battery is an electrochemical cell. It separates two types of metal immersed within a strong ionic solution (electrolyte).

The property for the tendency of metals to exchange electrons is enhanced when immersed in a strong ionic solution, that allows the electrons to flow between the two different metals. This flow of charge is electricity.

The property for the tendency of metals to exchange electrons is enhanced when immersed in a strong ionic solution, that allows the electrons to flow between the two different metals. This flow of charge is electricity

KC 2 = The number and kinds of atoms in a moleculeIt doesn’t tell you the STRUCTURE.

Structural FormulasStructural FormulasShows you the specific arrangement of the atoms found in a substance

C6H12O6 C6H12O6

Isomers - same numbers and kinds of

atoms but different structures

ModelsModels

KC 13 = the configuration of noble gases

Covalent bonds usually contain the “greedy non-metals

Single Covalent Bond two atoms held together by a sharing of a pair of electronsKC 14 shared pairs are dotted in between

Or shown as a dashed line in a Formula

Unshared pairs - pairs of electrons that are not shared between two atoms

Double Bond = a bond from two shared pairs (4 electrons)Triple Bond = A bond from three shared pairs (6 electrons)

What is a coordinate covalent bond?One atoms contributes both shared electrons (its less greedy than the one it is bonding to)

Give an example of a coordinate covalent bond.Carbon Monoxide

KC 16 How is a coordinate covalent bond different from other covalent bonds?

The shared pair of electrons comes from one atom, not one from each

What is a polyatomic ion?A tightly bound group of atoms that has a charge, and yet behaves as a unit (package)

What is bond dissociation energy?Energy required to break a covalent bond between two atoms (Ex: H2 molecule = 435kJ/mol)

KC 17 How is the strength of a covalent bond related to its bond dissociation energy?

A large bond dissociation energy corresponds to a strong covalent bond.

Explain this idea in terms of carbon compounds, like methane and coal, and their relative stability.

Carbon and Hydrogen are equally strong in their pull, and therefore hard to separate = stable

Bond Dissociation Energies

KC 18 Draw the electron dot structure resonance structures of ozone and explain how they describe its bonding.Ozone is a hybrid, or mixture of the extremes of the

resonance formsWhat are resonance structures?

A structure that occurs when it is possible to draw two or more valid electron dot structures

KC 19 List three ways in which the octet rule can sometimes fail to be obeyed.

Cannot be satisfied in molecules whose total number of valence electrons is an odd number, there are also molecules in which an atoms has fewer, or more, than a complete octet (like NO2 page 228)

Draw the electron dot structure for sulfur hexafluoride. What is the unique application of sulfur hexafluoride.

Page 229

Sigma Bond = two atomic orbitals combine to form a molecular orbital that is symmetrical around the axis connecting the 2 nuclei

Pi Bond = the bonding electrons are found in sausage shaped regions above and below the bond axis

What is VSEPR theory?Valence Shell Electron Pair Repulsion Theory

KC 24 Explain how the VSEPR Theory can be sued to predict he shapes of molecules.

Repulsion between electron pairs causes molecular shapes to adjust so the valence-electron pairs stay as far apart as possible

Each bond counts as an area that shapes the molecule.

So does each set of unpaired electrons.

3

4

5

6

7

KC 34 Compare the strengths of intermolecular attractions to the strengths of ionic bonds and covalent bonds.

Weaker than ionic or covalent bonds

What are van der Waals forces?Two weakest molecular attractions caused by dipole interactions and dispersions

What are dipole interactions?Polar molecules attracted to one another

What are dispersion forces?The weakest force caused by the motion of electrons in a non-polar molecule from one side of the molecule to the other creating temporary dipole charges

What are hydrogen bonds?A specific type of dipole interaction when attractive forces in which a hydrogen covalently bonded to a very electronegative atom is also weakly bonded to an unshared pair of another electronegative atom

How does hydrogen bonding affect water?Surface tension

How does hydrogen bonding affect the structure of DNA?Attraction across the 2 different helixes, or base pairing is due to Hydrogen bonding