化学式和经验公式

• Chemistry is the study of matter and its properties as well as how matter changes

Chemical Formulae

• Chemical formula represents the number and type of atoms present in a molecule
• Empirical formula is the simplest whole number ratio of atoms in a compound
• Molecular formula is the actual number of atoms of each element in a molecule
• Structural formula shows the arrangement of atoms and bonds within a molecule

Calculating Empirical Formula

• Obtain the mass or percentage composition of each element
• Convert mass to moles by dividing by the respective atomic mass
• Divide each mole value by the smallest mole value to obtain the simplest mole ratio
• If the ratio isn't a whole number, multiply by a common factor to get whole numbers
• The whole number ratio represents the subscripts in the empirical formula

Calculating Molecular Formula

• Determine the empirical formula of the compound
• Calculate the empirical formula mass
• Divide the molecular mass by the empirical formula mass to find the multiplier
• Multiply the subscripts in the empirical formula by the multiplier to get the molecular formula

Relative Atomic Mass (Ar)

• The relative atomic mass is the average mass of an atom of an element on a scale where the mass of an atom of carbon-12 is 12 units
• It is a weighted average of the masses of the isotopes of an element

Relative Molecular Mass (Mr)

• The relative molecular mass is the sum of the relative atomic masses of all the atoms in its molecule based on the scale where the relative atomic mass of carbon-12 is 12
• This term is for covalent compounds

Relative Formula Mass

• Relative formula mass is the sum of the relative atomic masses of all the ions in its formula
• This term is for ionic compounds

Mole Concept

• A mole is the amount of substance containing the same number of particles (atoms, molecules, ions, etc.) as there are atoms in 12g of carbon-12
• One mole contains Avogadro's number (6.02 x 10^23) of particles

Molar Mass

• The mass of one mole of a substance is known as molar mass
• Molar mass is numerically equal to the relative atomic mass (for elements) or relative molecular mass (for compounds) expressed in grams

Molar Volume

• The volume occupied by one mole of a gas at standard temperature and pressure (STP) is 22.4 L or 22.4 dm^3
• At room temperature and pressure (RTP), the molar volume is 24.0 L or 24.0 dm^3

Stoichiometry

• Stoichiometry is the study of quantitative relationships between reactants and products in a chemical reaction

Stoichiometric Calculations

• Write the balanced chemical equation
• Convert given masses to moles
• Use the stoichiometric coefficients from the balanced equation to determine the mole ratios
• Convert moles of desired product back to mass or volume as required

Limiting Reactant

• The limiting reactant is the reactant that is completely consumed in a reaction
• It determines the maximum amount of product formed

Excess Reactant

• The reactant that is not completely consumed in a reaction

Concentration of Solutions

• Concentration is the amount of solute present in a given volume of solution
• Concentration can be expressed in molarity (M), which is moles of solute per liter of solution (mol/L)

Molarity Equation

• Molarity (M) = Moles of solute / Volume of solution (in liters)

Dilution

• Dilution is the process of reducing the concentration of a solution by adding more solvent
• M1V1 = M2V2, where M is molarity and V is volume

Atomic Structure

• An atom consists of a nucleus containing protons and neutrons surrounded by electrons in specific energy levels or shells

Subatomic Particles

• Protons are positively charged particles in the nucleus
• Neutrons are neutral particles in the nucleus
• Electrons are negatively charged particles orbiting the nucleus

Atomic Number (Z)

• The number of protons in the nucleus of an atom, which determines the element's identity

Mass Number (A)

• The total number of protons and neutrons in the nucleus of an atom

Isotopes

• Atoms of the same element with the same atomic number but different mass numbers due to different numbers of neutrons

Electronic Configuration

• The arrangement of electrons in the different energy levels or shells around the nucleus
• Electrons fill the shells according to specific rules, such as the Aufbau principle and Hund's rule

Valence Electrons

• Electrons in the outermost shell of an atom
• Determine the chemical properties of an element and its ability to form bonds

Octet Rule

• Atoms tend to gain, lose, or share electrons in order to achieve a full outer shell with eight electrons (or two electrons for hydrogen and helium)

Types of Matter

• Matter exists in three common states: solid, liquid, and gas
• Plasma is another state of matter at very high temperatures

Solids

• Have a definite shape and volume
• Particles are closely packed and have strong intermolecular forces

Liquids

• Have a definite volume but take the shape of their container
• Particles are close but can move around, having moderate intermolecular forces

Gases

• Have no definite shape or volume and expand to fill their container
• Particles are far apart and move randomly, with weak intermolecular forces

Changes of State

• Melting: Solid to liquid
• Freezing: Liquid to solid
• Boiling/Evaporation: Liquid to gas
• Condensation: Gas to liquid
• Sublimation: Solid to gas
• Deposition: Gas to solid

Kinetic Molecular Theory

• Matter is composed of particles in constant motion
• The kinetic energy of particles increases with temperature
• Intermolecular forces exist between particles, affecting their behavior

Diffusion

• The movement of particles from an area of high concentration to an area of low concentration
• Occurs more rapidly at higher temperatures

Brownian Motion

• The random movement of particles suspended in a fluid (liquid or gas) resulting from collisions with the fast-moving molecules of the fluid

Methods of separating mixtures

• Filtration: Separates insoluble solids from liquids
• Evaporation: Separates soluble solids from liquids
• Distillation: Separates liquids with different boiling points
• Chromatography: Separates substances based on their different affinities for a stationary phase and a mobile phase
• Magnetism: Separates magnetic substances from non-magnetic substances
• Separating funnel: Separates immiscible liquids