Chemistry notes

Protons:
- Positively charged (+).
- Mass of 1 amu.
- Determine nuclear charge.
  Example: Which has the greatest nuclear charge? Cl-35, Ar-40, K-39, Ca-40
Neutrons:
- No charge.
- Mass of 1 amu.
- Located in the nucleus (nucleons).
  Example: Which has the greatest number of nucleons? Sn-119, Sb-122, Te-128, I-127
Electrons:
- Negatively charged (-).
- Negligible mass (almost 0 amu).
- Found in "clouds" (orbitals) around the nucleus.
Nucleus:
- Contains protons and neutrons.
- Most of the mass of an atom is found in the nucleus.
Electron Cloud (Orbitals):
- Most of the size (volume) of an atom is due to the electron cloud.

Mass Number:
- Sum of protons and neutrons.
- $Mass\ Number = Number\ of\ Protons + Number\ of\ Neutrons$
  Example: What is the mass number of an atom with 18 protons and 22 neutrons? (Answer: 40)
Atomic Number:
- Number of protons in the nucleus.
  Example: Which has the greatest atomic number? S, Cl, Ar, K
Number of Neutrons:
- $Number\ of\ Neutrons = Mass\ Number - Atomic\ Number$
  Example: Which correctly represents an atom of neon containing 11 neutrons? 11Ne, 21Ne, 20Ne, 22Ne
Neutral Atom:
- $Number\ of\ Protons = Number\ of\ Electrons$

Isotopes:
- Atoms with the same number of protons but different numbers of neutrons.
- Two isotopes of the same element have the same number of protons and electrons.
Ions:
- Cations:
  - Positive ions (+).
  - Formed when a neutral atom loses electrons.
  - Smaller than their parent atom.
    Example: Which of the following will form an ion with a smaller radius than that of its atom? Cl, N, Br, Ba
- Anions:
  - Negative ions (-).
  - Formed when a neutral atom gains electrons.
  - Larger than their parent atom.
    Example: Which electron configuration is correct for a fluoride ion? 2-7, 2-8, 2-8-1, 2-6

Rutherford's Gold Foil Experiment:
- Demonstrated that an atom is mostly empty space with a small, dense, positively charged nucleus.
Thomson's Plum-Pudding Model:
- Discovered the electron.
- Proposed a model with positive and negative particles spread throughout the atom.
Dalton's Model:
- Solid sphere of matter that was uniform throughout.
Bohr Model:
- Electrons in "planet-like" orbits around the nucleus.
Wave-Mechanical Model (Current Model):
- Electrons in "clouds" (orbitals) around the nucleus.

Excited Electrons:
- Electrons can jump to higher energy levels when excited.
Light Emission:
- Emit energy as light when they fall from higher energy levels back to lower (ground state) energy levels.
- Bright line spectra are produced.

Elements:
- Pure substances composed of atoms with the same atomic number.
- Cannot be decomposed.
Compounds:
- Can be decomposed.
- Have a homogeneous composition
- Have one set of properties
  Example: A compound differs from an element in that a compound Has a homogeneous composition has one set of properties Has a heterogeneous composition can be decomposed
Binary compound:
*Substances made up of only two kinds of atoms
Ternary Compound:
*Contain three or more kinds of atoms
*Example:* Which substance is a binary compound? Ammonia, magnesium, potassium nitrate, methanol
Diatomic Molecules:
- Elements that form two-atom molecules in their natural form at STP.
  Example: Which element is a diatomic liquid at STP? Chlorine, fluorine, bromine, iodine

Pacific vs. Atlantic Rule:
- Pacific (Decimal Present): Start counting digits from the left side, starting with the first non-zero digit.
  Example: 0.003100 (4 sig. figs.)
- Atlantic (Decimal Absent): Start counting digits from the right side, starting with the first non-zero digit.
  Example: 31,400 (3 sig. figs.)

Measurements:
- Involve mass and volume.
- Measured in the lab by displacement.
Volume of object by displacement:
- $Volume\ of\ object = Volume\ of\ water + object - Volume\ of\ water$
  Example: Mass of object measured in lab by the displacement of water according to the data below: Mass of object 23.6 g Volume of water: 15.0 mL Volume of water + object: 18.2 mL
Homogeneous vs. Heterogeneous Mixtures:
*Homogeneous: Have discernible components and are uniform throughout
*Heterogeneous: Do not have discernible components and are not uniform throughout
*Air is classified as a homogeneous mixture
Solutions:
- Homogeneous mixtures.
- The solute is the substance being dissolved.
- The solvent is the substance doing the dissolving.
  Example: Substance NaCl (s) is added to water. The solute is the solvent is _

Isotopes:
- Written in a number of ways, including notation with atomic number and mass number.
  Example: $^{14}C_6$
- $Mass\ Number = Number\ of\ Protons + Number\ of\ Neutrons$
- $Number\ of\ Neutrons = Mass\ Number - Atomic\ Number$
- C-14 is also carbon-14, and is an isotope of carbon
Average Atomic Mass:
- Weighted average of all the known isotopes of an element.
- Calculated using the percent abundance of each isotope.
  Example: Find the average atomic mass of lithium if 7.4 % are 6Li and 92.6% are 7Li

Electron Configuration:
- Distribution of electrons in an atom.
- Written in the bottom center of an element’s box on the periodic table.
- Outermost electrons are the valence electrons.
  *# of electrons in 2 = *# of electrons in 8 =
  *# of electrons in 3 = __

Mole Map:
- Use the mole map to help you solve conversions between moles, grams, liters of gases at STP, and numbers of molecules/atoms.
- In measurement final answer must have as many digits as the element with the fewest digits.

Empirical Formula:
- The simplest whole number ratio of elements in a compound.
Molecular Formula:
- The actual number of atoms of each element in a molecule.
  Example: Given the empirical formula NO2. Find its molecular formula if the molar mass = 92g. (Answer: $N<em>2O</em>4$ )

Kinetic Molecular Theory:
- Explains the behavior of matter as particles with energy and motion.
Solids:
- Particles are rigidly held together in a lattice-type regular geometric arrangement.
- Have a definite shape and volume.
Liquids:
- Have closely-spaced particles that easily slide past one another; they have no definite shape, only a definite volume.

Chemical Formulas:
- Are written so that the charges of cations and anions neutralize.
  Examples:
- Positive ion (cation) first followed by the name of the product with the name ending in “-ide.”
- Calcium phosphate: $Ca^{2+} PO_4^{3-}$
- Write the name of the ratio of $$"MgS