Introduction to Chemistry

• Chemistry is the study of matter and its properties as well as how matter changes.
• Matter is anything that has mass and takes up space (volume).
• A chemical is a substance with a defined composition that does not vary.
• Properties are characteristics that allow us to distinguish types of matter.
• Physical properties are characteristics that do not involve a change in chemical identity.
• Examples of physical properties include: mass, color, volume, and temperature.
• Chemical properties describe how a substance will change or react to form other substances.
• Examples of chemical properties include: flammability, corrosivity, and reactivity with acid.
• Matter can exist in three states: solid, liquid, and gas.
• Solids have a definite shape and volume.
• Liquids have a definite volume but take the shape of their container.
• Gases have no definite shape or volume and expand to fill their container.
• A pure substance has a fixed composition and distinct properties.
• Mixtures are combinations of two or more substances in which each substance retains its chemical identity.
• Homogeneous mixtures have uniform composition throughout.
• Heterogeneous mixtures do not have uniform composition.
• Elements are substances that cannot be broken down into simpler substances by chemical means.
• Compounds are substances composed of two or more elements chemically united in fixed proportions.
• Chemical formulas represent compounds, indicating the elements and their ratios.
• The law of definite proportions states that a given chemical compound always contains its component elements in fixed ratio (by weight) and does not depend on its origin and method of preparation.
• Mass is a measure of the amount of matter in an object.
• Weight is the force exerted on an object by gravity.
• The SI system is the standard system of units used in science.
• Length is measured in meters (m).
• Mass is measured in kilograms (kg).
• Time is measured in seconds (s).
• Temperature is measured in Kelvin (K).
• Volume is measured in cubic meters (m^3), but liters (L) and milliliters (mL) are more commonly used in chemistry.
• Density is the ratio of mass to volume, typically expressed in g/cm^3 or g/mL.
• Temperature is a measure of the average kinetic energy of the particles in a sample.
• The Kelvin scale is an absolute temperature scale, where 0 K is absolute zero.
• Celsius is commonly written in °C, and Kelvin is simply K.
• Celsius to Kelvin conversion: K = °C + 273.15.
• Fahrenheit to Celsius conversion: °C = 5/9(°F - 32).
• Accuracy refers to how close a measurement is to the true or accepted value.
• Precision refers to how close a series of measurements are to one another.
• Significant figures indicate the precision of a measurement.
• Rules for significant figures involve counting all non-zero digits, zeros between non-zero digits, and trailing zeros to the right of a decimal point.
• Rules for significant figures in calculations: For multiplication and division, the result contains the same number of significant figures as the measurement with the fewest significant figures.
• Rules for significant figures in calculations: For addition and subtraction, the result has the same number of decimal places as the measurement with the fewest decimal places.
• Dimensional analysis is a method of problem-solving that uses the units to guide the calculations.
• Conversion factors are used to convert between different units.

Atomic Structure

• Atoms are the basic building blocks of matter.
• Atoms consist of protons, neutrons, and electrons.
• Protons have a positive charge and are located in the nucleus.
• Neutrons have no charge and are located in the nucleus.
• Electrons have a negative charge and orbit the nucleus.
• The atomic number (Z) is the number of protons in an atom's nucleus, defining the element.
• The mass number (A) is the total number of protons and neutrons in an atom's nucleus.
• Isotopes are atoms of the same element with different numbers of neutrons.
• Ions are formed when atoms gain or lose electrons.
• Cations are positively charged ions formed by losing electrons.
• Anions are negatively charged ions formed by gaining electrons.
• The periodic table organizes elements by increasing atomic number and groups them with similar properties.
• Groups (vertical columns) share similar chemical properties.
• Periods (horizontal rows) show trends in properties.
• Metals are typically shiny, conductive, and malleable, tending to lose electrons to form positive ions.
• Nonmetals are typically dull, non-conductive, and brittle, tending to gain electrons to form negative ions.
• Metalloids have properties intermediate between metals and nonmetals.
• Molecules are two or more atoms held together by chemical bonds.
• Chemical formulas indicate the number and type of atoms in a molecule.
• Empirical formulas give the simplest whole-number ratio of atoms in a compound.
• Molecular formulas give the actual number of atoms of each element in a molecule.
• Structural formulas show the arrangement of atoms and bonds in a molecule.
• Ionic compounds are formed by the electrostatic attraction between oppositely charged ions.
• Covalent compounds are formed by the sharing of electrons between atoms.
• Naming ionic compounds involves naming the cation first, followed by the anion with an "-ide" ending.
• Naming covalent compounds involves using prefixes to indicate the number of atoms of each element (mono-, di-, tri-, etc.).

Chemical Reactions

• A chemical equation represents a chemical reaction using chemical formulas and symbols.
• Reactants are the substances that undergo change in a chemical reaction.
• Products are the substances that are formed in a chemical reaction.
• Stoichiometry is the study of the quantitative relationships between reactants and products in a chemical reaction.
• The law of conservation of mass states that matter cannot be created or destroyed in a chemical reaction.
• Balancing chemical equations involves adjusting stoichiometric coefficients to ensure that the number of atoms of each element is the same on both sides of the equation.
• The mole (mol) is the SI unit for the amount of substance, defined as the amount of substance containing as many elementary entities as there are atoms in exactly 12 grams of carbon-12.
• Avogadro's number (6.022 x 10^23) is the number of entities (atoms, molecules, ions, etc.) in one mole.
• Molar mass is the mass of one mole of a substance, expressed in grams per mole (g/mol).
• Limiting reactant is the reactant that is completely consumed in a chemical reaction and determines the amount of product formed.
• Excess reactant is the reactant that is present in a greater amount than necessary to react completely with the limiting reactant.
• Theoretical yield is the maximum amount of product that can be formed from a given amount of reactants, assuming complete conversion of the limiting reactant.
• Actual yield is the amount of product actually obtained in a chemical reaction.
• Percent yield is the ratio of the actual yield to the theoretical yield, expressed as a percentage.
• Percent yield = (Actual yield / Theoretical yield) x 100%.