Key Concepts in Chemistry: Elements, Compounds, and Reactions

Element

Substance with identical atomic number atoms.

Compound

Two or more elements chemically bonded together.

Physical Change

Rearrangement of particles without altering substance.

Chemical Change

Formation of new substances with different properties.

Endothermic

Process that absorbs heat energy.

Exothermic

Process that releases heat energy.

Phases of Matter

Solid, liquid, and gas states of substances.

Solid

Has fixed volume and shape with rigid structure.

Liquid

Has fixed volume but changing shape, mobile particles.

Gas

No fixed volume or shape, fills container completely.

Heating Curve

Graph showing temperature changes during phase transitions.

Heat of Fusion (H+)

Energy to convert solid to liquid per gram.

Heat of Vaporization (Hy)

Energy to convert liquid to gas per gram.

Specific Heat (C)

Energy needed to raise 1g by 1°C.

Specific Heat of Water

1 cal/gJ or 4.2 J/gK.

Combined Gas Law

Relationship between pressure, temperature, and volume.

Kinetic Molecular Theory (KMT)

Describes behavior of ideal gases and particle motion.

Ideal Gas

Gas behaving according to KMT assumptions.

Real Gas

Closest to ideal at low temperature, high pressure.

Law of Conservation of Energy

Energy cannot be created or destroyed, only transformed.

Heat Transfer

Energy movement from higher to lower temperature.

Temperature

Measure of average kinetic energy of particles.

Kinetic Energy

Energy of motion, affecting physical processes.

Potential Energy

Stored energy based on position or configuration.

Exothermic Process

Releases heat, warms surrounding environment.

Endothermic Process

Absorbs heat, cools surrounding environment.

Periodic Table

Arrangement of elements by atomic number.

Atomic Number

Number of protons in an atom's nucleus.

Atomic Mass

Sum of protons and neutrons in nucleus.

Electronegativity

Tendency of an atom to attract electrons.

First Ionization Energy

Energy needed to remove the outermost electron.

Metallic Character

Tendency of an element to exhibit metallic properties.

Allotropes

Different forms of the same element in same phase.

Chemical Formula

Representation of a compound's elements and proportions.

Empirical Formula

Simplest whole number ratio of elements in a compound.

Molecular Formula

Actual number of atoms of each element in a molecule.

Structural Formula

Shows arrangement of atoms and types in a molecule.

Conservation of Mass

Mass remains constant in chemical reactions.

Balanced Chemical Equation

Represents equal number of atoms on both sides.

Mole Ratio

Ratio of coefficients in a balanced equation.

Molar Mass

Mass of one mole of a substance.

Percent Composition

Mass percentage of each element in a compound.

Types of Reactions

Includes synthesis, decomposition, single and double replacement.

Solution

Homogeneous mixture of solute in solvent.

Solubility Factors

Depends on temperature, pressure, and solute-solvent nature.

Isotopes

Atoms of the same element with different neutrons.

Isotopic Notation

Representation of isotopes, e.g., C-14.

Metals

Elements that conduct electricity and heat well.

Non-metals

Elements that lack metallic properties.

Metalloids

Elements with properties of both metals and non-metals.

Noble gases

Inert gases with filled valence shells.

Density

Mass per unit volume of a substance.

Conductivity

Ability of a substance to conduct electricity.

Malleability

Ability to be shaped or deformed without breaking.

Hardness

Resistance of a material to deformation.

Ductility

Ability to be drawn into wires.

Solubility

Ability of a substance to dissolve in a solvent.

Chemical properties

Behavior of an element in chemical reactions.

Periods

Horizontal rows in the Periodic Table.

Groups

Vertical columns in the Periodic Table.

Valence configuration

Arrangement of electrons in the outer shell.

Alkali metals

Group 1 elements, highly reactive, excluding hydrogen.

Alkaline earth metals

Group 2 elements, reactive metals.

Halogens

Group 17 elements, highly reactive non-metals.

Atomic radius

Distance from nucleus to outermost electron.

Ionization energy

Energy required to remove an electron from an atom.

Saturated solution

Solution where solute and solvent are in equilibrium.

Collision theory

Reactions occur when particles collide effectively.

LeChatelier's principle

Predicts system response to changes in equilibrium.

Heat of reaction

Energy change during a chemical reaction.

Entropy

Measure of disorder or randomness in a system.