Pre-IB Chemistry

Matter

Significant Digits/Figures

The actual digits measured by an instrument. Precision is determined by one place value greater than the smallest marking on the instrument.

Rules for Determining Number of Significant Digits

- All nonzero digits are significant

- If the last digit is 0 and preceded by a decimal

- All zeros between significant digits are significant

When adding and subtracting, round to the least precise place.

When multiplying and dividing, round to the lowest number of significant digits.

To show significance of a zero you could: add a decimal point, add a line above, or write in scientific notation.

Properties of Matter

PHASE CHANGES

There are six types of phase change:

- Solid to liquid is melting

- Liquid to solid is freezing

- Liquid to gas is evaporation

- Gas to liquid is condensation

- Solid to gas is sublimation

- Gas to solid is deposition

DIAGRAMS

- They occur with the addition/removal of heat

- Occur when temperature remains

PROPERTIES

- Physical properties are observed without changing the substance

- Chemical properties are observed with changes or reactions.

- Extensive properties depend on amount present

- Intensive properties are not dependent on amount (all chemical)

Types of Matter

ELEMENTS

- Consists of only one type of particle (atom)

- Pure substance

- Homogeneous

- Cannot be broken down

- Represented by a symbol

- Found on the periodic table

COMPOUNDS

- Consist of only one particle: molecules of multiple elements.

- Pure substance

-Homogeneous

- Separable with chemical methods

- Composed of elements in ratios

- Represented by a formula

MIXTURES

- Two or more different particles

- Homogeneous or heterogeneous

- Separable physically and chemically

- Composed of phases and interfaces

ex: pizza

phases interfaces

pepperoni pepperoni-cheese

sauce dough/sauce

cheese cheese/sauce

onion onion/cheese

dough

Atoms

Atomic Theory

- Aristotle thought all matter was made of four elements (earth, wind, water, fire).

- Democritus believed that matter was made of indivisible particles (atomos).

- Dalton proposed modern atomic theory:

  1. Matter is made of atoms

  2. Same elements are made of same atoms (false)

  3. Atoms cannot be created nor destroyed (false)

  4. Their combinations form chemical reactions and compounds.

- Thomson performed cathode ray experiments and discovered electron. Developed "plum pudding" model.

- Rutherford performed gold foil experiment and discovered the nucleus (proton).

- Bohr developed solar system model of the atom. Though, he only studied hydrogen.

- Wave Model, by Schrödinger and Heisenberg, states that electrons are in probability clouds.

Atomic Structure

Protons | Neutrons | Electrons

Positive | No charge | Negative charge

in nucleus | Found in nucleus | nucleus and clouds

m: 1 amu | m: 1 amu | m: ~0 amu

Rutherford | Chadwick | Thomson

- The atomic number is the number of protons - determines the element.

- The mass is determined by P+N

- Electron number is equal to protons.

Average Atomic Mass

- Weighted average of the relative abundance of each isotope

- An Isotope has the same number of protons, with a different neutron count.

- Average Mass = Σpm

Mass Spec

[Graph showing:

x-axis: Mass

y-axis: Amount%

Three peaks at masses 10, 11, and 12

Highest peak at mass 11]

Σ a/40 Q = 10.88

Electron Distribution

- Electrons are located in energy levels which are subdivided into sublevels and orbitals.

- Energy Levels: 1-7

- Electrons held: 2n²

SUBLEVELS

s: 1 orbital - 2 electrons max

p: 3 orbitals - 6 electrons max

d: 5 orbitals - 10 electrons max

f: 7 orbitals - 14 electrons max

ORDER

- 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p

RULES

- Aufbau Principle: electrons fill lower energy levels before filling higher energy levels

- Hund's Rule: electrons in a sublevel will fill each orbital before pairing up.

- Pauli Exclusion Principle: electrons in the same orbital will have different spins.

ORBITAL NOTATION

- Graphically represents the distribution of electrons.S

Moles and Formulas

Bonding

Sigma and Pi Bonds

Sigma: All single bond sand 1 of the bonds in a multiple

Pi: The remaining bonds in a multiple bond that are not sigma.

Polar Molecules

  • Caused by uneven distribution of electrons.

  • Result when polar bonds are arranged in an asymmetric shape molecule (bent, trigonal, pyramidal, see-saw, T-shaped, square-pyramid) or when there are different atoms around the center of a symmetrically shaped molecule.

Intermolecular Forces

Forces between molecules that help determine properties of the substance.

Stronger IMF result in substance having a higher melting/boiling point, viscosity, and cohesive forces.

3 Types:

  1. London Dispersion: weakest and result from random polarization of a molecule due to movement of electrons (low melting/boiling points). Occurs in all substances, polar or nonpolar. Higher molecular weight results in higher London Dispersion.

  2. Dipole-Dipole: Result between polar molecules when positive end of one molecule attracts the negative end of another molecule (high melting/boiling points.)

  3. Hydrogen Bonding: Strong dipole-dipole bond that involes a molecules with hydrogen and nitrogen, oxygen, or fluorine. This is the reason for water’s special properties.

Test Review: Bonding

Multiple Choice/Short Answer

  1. Distinguish between ionic, covalent, and metallic bonds based on characteristics and descriptions.

  2. Given either a periodic table or a table of electronegativies, predict the bond type.

  3. Draw Lewis Dot symbols for elements and count valence electrons

  4. Apply Octet Rule to draw models.

  5. Identify shapes and electron domains.

  6. Identify bond angles.

  7. Identify hybridization of central atoms.

  8. Identify sigma and pi bonds.

  9. Determine polarity.

  10. Distinguish between IMF’s and apply properties.

Moles and Stoichiometry

Types of Chemical Reactions

Five Types

  1. Synthesis: multiple reactants to make one product. A+B > AB

  2. Decomposition: one reactant makes multiple products. AB > A+B

  3. Single Replacement/Displacement: element and compound react to produce a different element and compound.

  4. Double Replacement/Displacement: two compounds exchange cations to produce two different compounds. AB+CD > AD+CB.

  5. Combustion: A carbon compound reacts with gas, producing carbon dioxide and water. CH4 + O2 > CO2 + H2O

Predicting Products

  • Binary compound: Product is the two elements in the compound

  • Reactant is a metal carbonate: Product is a metal oxide and carbon dioxide

  • Reactant is a metal chlorate: Product is a metal chloride and oxygen

  • Reactant is two elements: Product is a binary compound

  • Reactant is a metal oxide and water: Product is a metal hydroxide

  • Reactant is a nonmetal oxide and water: Product is an acid (H and polyatomic)

  • Reactant is an element and a compound: Product is an element and a compound (“likes” replaces “likes”). Single element must be above compound element in series).

  • Reactant is two compounds: Product is two compounds (switch the first ions)

  • Product is a carbon compound with oxygen: Products are carbon dioxide and water

Stoichiometry

  • Shows the mathematical relationships within a balanced equation.

  • Equation must be balanced to solve a stoichiometry problem.

Steps:

  1. Change given(s) to moles

  2. Convert to the new substance using coefficient ratios

  3. Change to unit wanted

Limiting Reactants/Reagants

  • Limit or restrict the amount of product produced.

  • Limiting reactant is consumed during the reaction.

  • Excess reactant remains after the limiting reactant used up.