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Unit 4 - Chemical attractions

LANGUAGE DEVELOPMENT

polarity - uneven distribution of particles in a molecule —> hydrogen bonding
law of conservation of mass - starting materials = ending materials
chemical equation - reactants and products separated with + signs and the production of new substances with —>
mole - 6.022 × 10²³ particles
solution - solute + solvent
solubility - ability of a solute to dissolve in a solvent
concentration - amount of substance in a defined space

4.1 - properties of materials

exploration 1 - observing properties of compounds

ideas
- materials have no overall charge because they have equal numbers of protons and electrons
- electric force/Coulomb force - repulsions + attractions due to electric charge

ionic compounds - strong attractive forces hold ions tightly together —> high melting point
molecular compounds - attractive forces still exist —> low melting point

uneven molecular charges
- electronegativity - tendency of an atom to pull electrons towards itself
- nonpolar covalent bond - two atoms from the same element form a covalent bond, evenly sharing electrons
- polarity - uneven distribution of particles in a molecule
  - polar molecule - a partial negative charge on one end, and a partial positive charge on the other —> poles
    - partial charge - unequal sharing (covalent bonds)
  - dipole - molecule w/ two poles
  - diatomic - having 2 atoms
  - 2+ atoms - polarity is determined by polarity of individual bonds + 3D arrangement of molecules
    - 3D arrangement - H2O molecule has 2 dipoles. Since it is bent, the arrangement isn’t symmetrical. —> water is highly polar b/c there are 2 unshared electrons on the oxygen atom
      - negative center of charge - around oxygen atom
      - positive center of charge - between 2 hydrogen atoms
      - BOTH RESULT IN HIGH SURFACE TENSION + BOILING POINT

dipole-dipole forces
- heat = energy added to a system
- KE increases in a liquid’s molecules and they move faster
- boiling point - molecules move fast enough to overcome attractive forces between molecules —> pulling away from each other entering gas state
- stronger forces are between molecules = higher boiling point

ICl is a polar molecule, whereas Br₂ is nonpolar. The boiling point of ICl is likely to be higher than the boiling point of Br₂. This is due to dipole-dipole interactions between positive and negative portions of polar molecules.
dipole-induced dipole - attraction is a weak attraction that occurs when a polar molecule causes a dipole to form in an atom or nonpolar molecule by disrupting the electron configuration in the nonpolar atom.
A dipole-induced dipole interaction is much weaker than a dipole-dipole interaction because the electrons in the nonpolar atom are shifted to one side of the nucleus in a way that is not sustainable. The shift lasts for only an instant because electrons are in constant motion. —> needs to be balanced?

hydrogen bonding
- hydrogen compounds have unusually high boiling points
- bonded to a highly electronegative atom —> pulls electron almost completely away—> strong partial positive charge —> polar
ATTRACTION BETWEEN MOLECULES WITH HYDROGEN IN IT!!!
properties of water
- relatively small mass/size
- surface tension
- climbs up tube - CAPILLARY ACTION
- bubble shape —> cohesion between molecules
- expands when frozen —> loses KE = more bonds forming —> fixed distance
- liquid—>gas = broken bond
The amount of space between molecules in solid water is GREATER than that of liquid water. Density of solid water is LESS than that of liquid water. Substances with lower density FLOAT in substances with higher density.

London dispersion forces
- electrons = constant motion
- slightly uneven distribution
- temporary = + pole/ - pole
- induces dipoles in nearby atoms
- weak dipoles = constant motion
  - LONDON DISPERSION FORCE
- exists in every type of atom —> also nonpolar
- increases with atomic/molar mass
  - halogens
    - light = fluorine/chlorine = gases at room temp
    - large = bromine = liquid
    - largest = iodine = solid

exploration 3 - materials science and design

structure of materials
- materials science - scientific study of properties/applications of materials
- alloys - combining different metals that have different properties from their components
- metallic bonding - valence electrons shared by the entire solid
  - thermal/electric conductivity, malleability, ductility, reflect light from shiny surfaces
  - metal ions exist in a sea of electrons
  - electrons = free to move between ions
- ceramic - not metallic/organic
  - hard/chemically non-reactive
    - SOME are conductors
  - used to make diverse products
- semiconductors - electrical conductivity values between conductors and insulators
organic chemist
- organic chemistry - field of study focusing on chemistry of carbon-based molecules (like in living things)
- structure/function of proteins, carbohydrates, DNA, lipids
- how they are produced in the body
- molecule interactions
- how health is affected
- x-ray crystallography
- molecular modeling
- spectroscopy

* hydrogen bonding if paired with nitrogen/oxygen/fluorine

4.2

exploration 1 - analyzing the composition of matter

Antoine Lavoisier - total amount of matter before/after reaction = the same
- law of conservation of mass - starting material = ending material
- law of definite proportions - elements are always in a fixed ratio
- law of constant composition - chemical compounds contain fixed/constant proportions of their constituent elements
  - parts of a whole
- law of multiple proportions - atoms can rearrange to form new elements
  - dont break apart

exploration 3 - modeling chemical reactions

chemical equations - reactants and products are separated by +’s and —>’s
- balancing chemical equations
  - coefficients - indicates amount of each reactant/product
    - multiply subscripts by coefficients —> determine # of atoms
  - adjust each coefficient until each side is the same
patterns in types of reactions
1. synthesis - A+B —> AB
2. decomposition - AB —> A+B
3. single displacement - A + BD —> AD + B
4. double displacement - AC + BD —> AD + BC
5. combustion - CxHx + 02 —> CO2 + H20
  - chemical energy in the reactants is converted to thermal energy when the fuel is ignited. The fuel reacts with oxygen in the air to form the products carbon dioxide and water. Using combustion engines leads to a increase in the amount of energy stored in earths atmosphere.

exploration 4 - quantifying matter in chemical reactions

mole ratios
- 2:2
- 1:2 or 2:1
particles - 6.02 × 10²³ in a mole

one mole of sugar has a different mass than one mole of salt. The mass of 1 mole of a substance depends on the chemical makeup of the substance. The number of particles in a mole does not depend on the identity of a substance.

exploration 5 - limiting and excess matter

limit - runs out first
excess - reactant that has extra left over

4.3

exploration 2 - describing solutions

solution = solvent + solute
- homogenous
  - solvent dissolves the solute
    - solute - dissolves
    - solvent - does the dissolving
- impacted by: molecular movement
  - stirring, size, substance its in, temperature, surface area
dissolution - a solute breaks down and mixes uniformly with a solvent
recrystallization - collisions form crystals again
equilibrium - both occur at the same rate
- saturated - maximum amount of dissolved solute
- unsaturated - increased amount of solvent

solubility - ability of a solute to dissolve in a solvent
- temperature/pressure
  - increased temperature = increased solubility
    - super satured = unstable
  - physical disturbance = recrystallization
aqueous solution - solvent is water
- universal
- polar
- hydration - charged parts of water molecule attract/surround positive ions
  - attract/surround negative ions of the solid

ionic compounds would be generally not soluble in nonpolar solvents. The nonpolar solvents do not have the charges necessary to draw ions out of the crystal into the solution

nonpolar
- fats, oils, greases
- do not easily dissolve in polar liquids
- imiscible = not soluble in each other
- miscible = dissolve freely

solubility + pressure
- increased = more collisions
  - more gas dissolves in a liquid
    - ex: carbonated beverage unopened —> most pressure
solubility + temperature
- increases with increasing temperature
- more KE
- increasing temperature decreases solubility in a gas
  - dissolving occurs more rapidly
- polarity

colloids/suspensions
- Suspension
  - heterogenous
  - large solutes that settle out the solution
    - ex: muddy water
- Colloids
  - smaller particles than present in suspensions
  - larger than in a solution
  - appear homogenous
  - large enough to scatter light —> Tyndall effect

exploration 3 - analyzing the behavior of solutions

dissociation - polar water molecules surround and separate the ions
ionization - polar covalent solute molecules from ions in solution

precipitation - mixing results in a combination of ions that form an insoluble compound
- attraction between ions > attraction between ions + surrounding water molecules
  - making pigments, removing salts from water (water treatment), chemical analysis
- patterns in solubility
  - palladium - dental fixtures —> low reacitivity
    - metal dissolved in chosen solvent (hydrochloric acid)

strong/weak electrolytes
- electrolyte - substance conducting electric current when dissolved in solution
  - yields ions
- non electrolyte - does not conduct electric current
  - does not yield ions
- strong: dilute aqeuous solutions conduct electricity well
- weak: forms fewer ions in water —> weaker conductivity

sodium chloride conducts electricity well because all of the dissolved compound forms ions. Acetic acid would conduct electricity poorly because some of the dissolved compound forms ions.

colligative properties
- pure water cannot conduct electricity
  - freezes at 0* C —> boils at 100* C
- salt water conducts electricity
  - freezes at a slightly lower temperature and boils at a slightly higher temperature
  - ex: salt melts icy roads, oceans have salt water so it is not completely solid
- dependent on the concentration of solute particles
- not dependent on the identity of solute particles
vapor pressure - pressure exerted by a vapor when the vapor is in equilibrium with the liquid or solid form, or both, of the same substance
osmotic pressure - external pressure applied to stop osmosis
- dependent on the concentration of solute particles