Fundamental Chemistry Concepts: Laws, States, and Bonding
Fundamental Chemical Laws
Law of Conservation of Matter (Lavoisier)
Matter is neither created nor destroyed, only transformed. The mass of the reactants equals the mass of the products.
Law of Definite Proportions (Proust)
Whenever two or more elements combine to form a compound, they do so in a constant mass ratio.
Law of Multiple Proportions (Dalton)
When two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other are in ratios of small whole numbers.
Law of Combining Volumes (Gay-Lussac)
In reactions between gases at constant pressure and temperature, the volumes of reactants and products are in ratios of small whole numbers.
Avogadro’s Hypothesis
Under the same conditions of temperature and pressure, equal volumes of different gases contain the same number of particles (molecules).
Atomic-Molecular Theory
The laws of Gay-Lussac and Avogadro, combined, completed Dalton’s atomic theory. Chemical elements are made of atoms, and some exist as molecules formed by atoms in definite proportions.
Relative Atomic Mass
The mass of an atom relative to one-twelfth the mass of a carbon-12 atom. It is a dimensionless number.
Unified Atomic Mass Unit (u or amu)
A mass unit equal to one-twelfth the mass of a carbon-12 atom (approximately 1.66 x 10-27 kg).
Mole (mol)
The amount of substance that contains as many elementary entities (atoms, molecules) as there are atoms in 12g of carbon-12 (approximately 6.022 x 1023).
Empirical Formula
The simplest whole-number ratio of atoms in a compound.
Molecular Formula
The formula indicating the actual number of atoms of each element in a molecule.
Percent Composition
The percentage by mass of each element in a compound.
States of Matter and Gas Laws
Boiling Point
The temperature at which a liquid changes to a gas throughout its volume. It coincides with the condensation point.
Melting Point
The temperature at which a solid changes to a liquid. It coincides with the freezing point.
Boyle’s Law
At constant temperature, the product of the pressure and volume of a gas is constant (P1V1 = P2V2).
Gay-Lussac’s Law
At constant volume, the ratio of the pressure and absolute temperature of a gas is constant (P1/T1 = P2/T2).
Charles’s Law
At constant pressure, the ratio of the volume and absolute temperature of a gas is constant (V1/T1 = V2/T2).
Dalton’s Law of Partial Pressures
In a gas mixture, the total pressure is the sum of the partial pressures of each component (PT = P1 + P2 + … + Pn).
Mole Fraction (Xi)
The ratio of the number of particles of a component to the total number of particles in a mixture. Partial pressure can be calculated as Pi = PT * Xi.
Atomic Structure and Periodicity
Isotopes
Atoms of the same element with the same number of protons but different numbers of neutrons (and thus different masses).
Spectrum
A set of characteristic wavelengths of electromagnetic radiation emitted or absorbed by a substance.
Valence Electrons
The electrons in the outermost energy level of an atom, responsible for its chemical behavior.
Valence (Ionic)
The number of electrons an atom gains or loses to achieve the nearest noble gas configuration. It’s negative if electrons are gained, positive if lost.
Periodic Properties
Properties of elements that vary predictably with their position in the periodic table.
Ionization Energy
The energy required to remove an electron from a gaseous atom (kJ/mol).
Electron Affinity
The energy released when a gaseous atom gains an electron (kJ/mol).
Electronegativity
The tendency of an atom to attract electrons in a covalent bond.
Metals
Elements with low electronegativity that tend to lose electrons and form positive ions.
Non-metals
Elements with high electronegativity that tend to gain electrons and form negative ions.
Chemical Bonding and Thermochemistry
Chemical Bonding
The forces holding atoms or molecules together in crystals, liquids, or solids.
Octet Rule
Atoms tend to bond in such a way as to achieve eight electrons in their valence shell.
Ionic Bond
Formed by the transfer of electrons between atoms, resulting in ions with noble gas configurations.
Covalent Bond
Formed by the sharing of electrons between atoms to achieve noble gas configurations.
Metallic Bond
Formed by the delocalization of electrons among metal atoms, allowing them to achieve noble gas configurations.
Thermochemistry
The study of energy changes in chemical reactions.
Heat of Reaction
The heat absorbed or released during a chemical reaction, often measured under standard conditions (25°C and 1 atm). Exothermic reactions release heat; endothermic reactions absorb heat.
Thermodynamics
The study of energy transformations, including the conversion of work to heat and vice versa.
Chemical System
A defined part of the universe separated from its surroundings by real or imaginary boundaries.