SL Chemical bonding and structures
Intermolecular vs Intramolecular forces
Intermolecular: Hold atoms together in a molecule (bonding forces of attraction). Determine molecular geometries, physical properties, and reactivities.
Intermolecular: Interactions between molecules in a compound. Responsible for melting and boiling points and such.
Intermolecular forces < Intramolecular forces
Dipole-Dipole forces
Exist between polar covalent molecules. Attraction between the slightly positive end of one molecule and the slightly negative end of another. Not as strong as ionic electrostatic attractions.
Induced Dipole-Dipole forces
Mixture of polar and non-polar molecules. Permanent dipoles cause temporary separation of charge on a non-polar molecule.
(+polar-) (non polar) ---> (+polar-) (+non polar-)
London Dispersion forces (LDF)
Attraction between positively charged nucleus and electrons of neighbouring atoms. Weaker than ionic and dipole-dipole forces. In all compounds and is the only intermolecular force that occurs between non-polar compounds. Creates a temporary dipole. Greater energy levels, greater LDF, greater boiling point.
Factors affecting LDF
1. Number of electrons that can be delocalized: The lower the Zeff, the more easily a temporary dipole can be induced.
2. Size of electron cloud: More energy levels, lower Zeff.
3. Shape of molecules: The greater contact area, the greater the LDF will be.
Hydrogen Bonding
NOT A VAN DER WAAL FORCE! H. O, F, and N are more electronegative than H (will be represented by X). The greater the difference in electronegativity, the greater the hydrogen bond. Y is an electronegative atom or anion that is attracted to Hydrogen. X-H --- Y-Z
Water molecules, Ammonia molecules, Hydrogen Fluoride molecules, and water molecules & dimethyl ether molecules (organic compound).
Hydrogen bonds are the strongest of the intermolecular forces. LDF<dipole-dipole<Hydrogen bond. Molecules with H-bond have the highest boiling point (H2O, HF, NH3)
ex. OH- and NH2 have a hydrogen bond
As you go down a group...
Zeff gets lower, LDF gets higher, and Boiling point gets higher.
Unique properties of water
H-bonding keeps water molecules together. H-bonding also makes ice less dense than liquid water. In ice, each water molecule forms H-bonds with adjacent water molecules creating a very ordered network with large spaces. In water, H-bonds are more random and result in a higher density.
Melting and Boiling points in polar vs non-polar covalent molecules
Non-polar: very low. O2, F2, CO2.
Polar: Intermediate. H2O, HCl, PCl3.
Hydrogen Bonds: Highest.
Solubility in polar vs non-polar covalent molecules
non-polar: insoluble. O2, F2, CS2.
polar: soluble. HCl, PCl3, Cl2O.
Conductivity of Molecules
Electrons that make up covalent bonds are not free to move around, meaning that molecules cannot conduct electricity. BUT, acids dissolved in water are an exception because they behave as an ionic compound when dissolved. ex: H-Cl + H2O makes an electron get transferred from H to Cl.
Volatility
Stronger the intermolecular forces, the higher the melting/boiling points and therefore the lower the volatility.
Chromatography and Intermolecular Forces
1. chromatography is used to separate a mixture.
Stationary phase: paper contains 10% water and forms H-bonds with the OH- groups in cellulose of paper.
Mobile phase: solvent rises up the paper by capillary action. The more soluble the component is, the further it will rise up the paper.
The position where the mixture starts is called the origin (not submerged in water). When the solvent almost reaches the top, the final position is marked and is known as the solvent front. The final result is called a chromatogram.
Retardation Factor (Rf) = distance moved by component / distance moved by solvent.
Thin Layer Chromatography
2. Thin layer chromatography is the same thing except during the stationary phase, it is made of a uniform layer of silicon dioxide or aluminum oxide coated onto a piece of glass/metal/plastic. the surface of both silica and alumina contains hydroxyl groups so are considered polar and able to form H-bonds with components in the sample.
Metallic Bonding
Metals have low Zeff and therefore valence electrons are not held in place very well, resulting in cations in a sea of delocalized electrons.
Metallic bond = electrostatic attractions between metal cations and delocalized electrons
Metallic bond strength
More valence electrons = stronger bond
Higher charge of metal = stronger bond
Smaller ionic radius = stronger bond
Higher melting point = stronger bond
Metallic bonding electrical conductivity
delocalized electrons can move around and carry the electric current.
Metallic bonding malleability
Malleability: ability of a solid to be flattened into a sheet/other shape without breaking.
Metallic bonds are non-directional meaning the cations can slide past one another, allowing them to be easily rearanged
Metallic bonding atomic radius across vs down
across a period: greater attraction between ions and delocalized electrons, higher melting point.
down a group: weaker attraction between ions and delocalized electrons, lower melting point.
Alloys
Mixture of two or more metals OR mixture of two or more metals and a non-metal (alloying element). They have enhanced properties; greater strength, greater resistance to corrosion, enhanced magnetic properties, and greater ductility.
How does alloying element work
it impacts non-directional bond making structure more rigid by making it harder for atoms to slip over each other. This alters the lattice.
The bonding triangle
three bonding models: ionic, covalent, and metallic. Some materials are fully one of the three, and some show intermediate properties. The structure of bonding is a continuum.
X-Axis: average of electronegativities
Y-Axis: difference in electronegativities
Going right along period 3, oxides' electronegativity differences get smaller, and so does ionic character.
Bonding triangle 3 properties
Ionic: top middle (ex.CsF)
Molecular: bottom right (ex. F)
Metallic: bottom left (ex. Cs)
Polymerization of Akenes
The reaction of many monomers that contains a carbon-carbon double bond linked together form a polymer.
What is Polyethene
Good electrical insulator used in bags and household containers, carrier bags, water tanks, etc. Produced by the addition of ethene monomers. Many polymers are used in the plastic industry. Many polymers are non-biodegradable.
Production of Polyethene
Ethene monomers are produced by the petrochemical industry then they supply them to the plastic industry. Ethene undergoes addition polymerization to form polymer polyethene (polyethylene).
Polymers two things
in the polymer... the double bond is replaced by a single bond. the electron pair released from the double bond forms a bond with an adjacent monomer.
Polypropene
Propene monomer. Uses: chains and water bottles.
Atom Economy
% atom economy = (molar mass of desired product / molar mass of all reactants) x 100
measure of the proportion of reactant that ends up in the desired product, based on the reaction's stoichiometry.
Polymerization doesn't produce byproducts so 100% of the reactants can be converted to products, but it's possible to have some unreacted monomer.
review test
pls
know how to draw
one monomer intro (polymer)n repeating
Group charges
1: +1
2: +2
13: +3
14: +4
15: -3
16: -2
17: -1
18: 0
bond angles
linear/trigonal linear: 180
bent: <120
trigonal: 120
tetrahedral: 109.5
trigonal pyramidal and other tetrahedrals: <109.5