Chemistry Notes

Atomic Theory

• Modern atomic theory states all matter is made up of atoms

• Atoms are composed of subatomic particles; protons (+), electrons (-), neutrons (neutral)

• Each element has an atomic number, which is equal to the number of protons in the nucleus

  • Atomic number dictates what the element is

  • A neutral atom will have the same number of protons and electrons

• Atomic mass is the combined number of protons and neutrons in the nucleus of an atom

• Particle: a general term that can refer to any small unit of matter, including atoms, molecules, compounds and ions

• Atom: the smallest unit of an element

• Molecule: a group of two or more atoms bonded together

  • All molecules are particles, but not all particles are molecules

• Ion: a positively or negatively charged particle 

  • Will either have more protons than electrons (+) or more electrons than protons (-)

  • Are ions regardless of positive or negative charge

  • Positive ion = cation

  • Negative ion = anion

  • Anions gain electrons, which make them more negatively charge, while cations lose electrons, meaning that they have more protons and are therefore positively charge

• Opposites attract; anions are attracted to positive poles which cations are attracted to negative poles

  • This helps atoms to achieve stability by covalent bonding, or sharing electrons with other atoms

• Octet rule explains that atoms strive to have eight valence electrons, which is stability in an atom

• Chemical reaction: a process that leads to the chemical transformation of one set of chemical substances into another

• Chemical reactions result in both a new substance and energy created

• Chemical equations illustrate reactions, and have the reactants on the left side and the products on the right side, separated by an arrow indicating direction of reaction

• Reaction types;

  • Synthesis: two or more reactants combine to create one new substance

  • Decomposition: a compound breaks down into simpler substances

  • Single replacement (displacement): one element replaces another in a compound

  • Double replacement (displacement): ions from two compounds exchange places to form new compounds

  • Combustion: a rapid reaction with oxygen, which always results in carbon dioxide and water, usually releasing heat a light

  • Acid-base (neutralization): reaction between an acid and a base where hydrogen ions are exchanged

  • Redox (oxidation-reduction): electrons are transferred between reactants, with one being oxidized and the other reduced

The Periodic Table (and Ions)

• Chemical symbol tells us which atom it is (C= carbon)

• Always begin with capital letter

• Isotopes are two of the same element with different masses, with a different number of neutrons

• Mass number is the total number of protons and neutrons in an atom (p+n)

• Atomic mass is the weighted average of the mass of all the isotopes of an element, so it is not often a whole number

• Electron notation;

  1. Number of shell

  2. Letter of orbital

  3. Number of electrons in orbital (as exponent)

• Bohr diagrams are models which show how electrons are arranged surrounding teh nucleus of an atom

• They are made up of orbitals and sublevels

• S sublevel: 1 orbital, 2 electrons

• P sublevel: 3 orbitals, 6 electrons

• D sublevel: 5 orbitals, 10 electrons

• F sublevel: 7 orbitals, 14 electrons

• Aufbau principle: electrons are filled into orbitals with the lowest energy level first, then progressing into higher energy levels

• How to make a Bohr diagram;

  1. Find element

  2. Determine the number of electrons (atomic number)

  3. Determine period

  4. Add electrons

• Drawing Bohr diagrams:

  1. Draw a nucleus at the center as the chemical symbol

  2. Identify energy levels or shells

  3. Draw shells around the nucleus

  4. Identify how many total you should have, and fill in the levels based on how many electrons each shell can hold

Properties of Matter

• Solid: molecules vibrate about a fixed point, cose together, definite shape and volume, not compressible

• Liquid: molecules are free to move,close together, indefinite shape, definite volume, somewhat compressible

• Gas: molecules are free to move, far apart, indefinite shape, indefinite volume, compressible

• A change in state of matter refers to a physical process where a substance transitions from one state to another 

• Melting: a solid turns into a liquid

• Freezing: a liquid turns to a olid

• Evaporation: a liquid turns to a gas

• Condensation: a gas turns to a liquid

• Sublimation: a sod turns to a gas

• Deposition: a gas turns to a solid

• Types of properties;

  • Qualitative: observations using words or symbols

  • Quantitative: observations sing numbers or statistics

  • Physical: observed and measured without changing chemical identity of a sample

    • Ex. color, density, state at room temp, electrical conductivity, solubility, melting point, 

  • Chemical: observed and measured as sample changes chemical identity

    • Ex. reactivity, burning, decomposition, rusting, rotting, corrosion

• Chemical change: change at the molecular level, alters the nature and properties of the substance, a new substance is formed

• Physical change: changes appearance or state but will not change molecular structure or give a new substance

Balancing & Stoichiometry

• Chemical equations are balanced by adjusting the coefficients until the number of atoms on both sides are equal

• This ensures the law of conservation of matter is followed

• Steps to balance an equation

  1. Count atoms

  2. Adjust coefficients

  3. Balance polyatomic ions as a unit

• Stoichiometry: the study of the quantitative relationship between reactants and products in a chemical reaction

• Analyzing how much of each substance is involved in a reaction based on the balanced chemical equation

  • Coefficients represent the relative number of moles of each reactant and products

  • Allows you to calculate mass, volume, or number of moles or a reactant or product given that of the other 

• The core concept in stoichiometry is the mole, which is the ratio of one substance to another in a reaction

• A mole is a unit used to measure the amount of a substance

• The amount of a chemical substance that contains exactly 6.022 x 10²³ elementary entities

• Elementary entity: a single, countable object like an atom, molecule, ion or a specifies group of atoms (particles)

• Avagadro’s number: the number of particles in one mole: 6.022 x 10²³ 

• Binding unit for stoichiometric conversions

• A mole to mole conversion refers to calculating how many models of one substance are produced or required by a chemical equation based on a known number of moles in another substance, using the coefficients from a balanced chemical equation

• Mole ratio from the balanced equation acts as the conversion factor 

• Mole to mole steps

  1. Write balanced chemical equations

  2. Identify known and unknown quantities

     • how many moles of the known substance you have, what you need to find

  3. Set up conversion factors

     • write the mole ratio from the balanced equation, placing the known in the denominator (bottom), and the unknown in the numerator (top)

  4. Multiply and cancel units

     • multiply known number of moles by the mole ratio

• Molar mass: the ratio between the mass and the amount of substance of any sample of the compound

  • The mass of one mole of a substance, usually found by adding up the up the atomic masses of all the elements in the compound based on ts chemical formula

• Steps

  1. Find the number of moles given in the problem 

  2. Look up the molar mass of the substance on the periodic table

  3. Multiply the number of moles by the molar mass to get the mass in grams

• M=m/n

  • M: molar mass

  • m: mass of substance in grams

  • n: number of moles in a substance

• To convert moles to molecules, you multiply the number of moles by Avagadro’s number

  • 6.022 x 10²³

• Molecules = moles x Avagadro’s number

• Ionic compounds use “formal units,” atoms use “atoms”