Cheat Sheet

Dalton's Atomic Theory

Dalton's Atomic Theory

Proposed by John Dalton. Elements are composed of indivisible particles called atoms. All atoms of the same element are identical in mass and properties. Compounds are formed by the combination of atoms in simple, whole-number ratios. Chemical reactions involve the rearrangement of atoms, and atoms are neither created nor destroyed.

Modern Atomic Theory

Atoms are the basic building blocks of matter. Atoms are composed of subatomic particles:Protons (positively charged) in the nucleus. Neutrons (neutral) in the nucleus. Electrons (negatively charged) orbiting the nucleus in electron clouds or energy levels. Elements are defined by the number of protons, known as the atomic number.

Subatomic Particles

Protons:Mass:~1 atomic mass unit (amu). Charge:+1. Neutrons:Mass:~1 amu. Charge:0. Electrons:Mass:~1/1836 amu (negligible). Charge:-1.

Atomic Structure

Atomic Number (Z):The number of protons in an atom. Mass Number (A):The sum of protons and neutrons in the nucleus. Isotopes:Atoms of the same element with different numbers of neutrons. Atomic Mass:Weighted average of the masses of all naturally occurring isotopes of an element.

The Periodic Table

Organizes elements based on atomic number and chemical properties. Groups (columns) have similar chemical properties. Periods (rows) represent the number of electron shells.

Atomic Models

Thomson's Model (Plum Pudding Model):Electrons embedded in a positively charged sphere. Rutherford's Model:Discovered the atomic nucleus, where most of the mass is concentrated. Bohr's Model:Electrons orbit the nucleus in discrete energy levels or shells. Modern Quantum Mechanical Model:Describes the behavior of electrons as waves and particles in electron clouds or orbitals.

Quantum Numbers

Principal Quantum Number (n):Represents the energy level or shell (n=1, 2, 3, ...). Angular Momentum Quantum Number (l):Determines the shape of the orbital (s, p, d, f). Magnetic Quantum Number (m_l):Specifies the orientation of an orbital in space. Spin Quantum Number (m_s):Describes the spin of an electron (up or down).

Electron Configuration

The arrangement of electrons in energy levels and orbitals. Follows the Aufbau principle, Pauli exclusion principle, and Hund's rule.

Periodic Trends

Atomic radius:Increases down a group, decreases across a period. Ionization energy:Decreases down a group, increases across a period. Electronegativity:Decreases down a group, increases across a period.

Chemical Bonding

Atoms form bonds to achieve a stable electron configuration. Types of bonds include covalent, ionic, and metallic.

Molecules and Compounds

Molecules are formed when atoms share electrons (covalent bonding). Compounds are substances composed of different elements in fixed ratios.

Nuclear Reactions

Involves changes in the nucleus. Examples include nuclear decay, fusion, and fission.

Modern Advances

The discovery of subatomic particles beyond protons, neutrons, and electrons, such as quarks and neutrinos. The development of quantum mechanics and its application to atomic theory.