Atomic Structure Overview

Atomic Structure

Basic Concepts
- Matter is composed of atoms, which are the smallest units of elements.
- Atoms consist of three main subatomic particles: protons, neutrons, and electrons.
Subatomic Particles
- Protons
  - Positively charged particles.
  - Located in the nucleus.
  - Determine the atomic number (Z) of an element.
- Neutrons
  - Neutral particles (no charge).
  - Also located in the nucleus.
  - Contribute to atomic mass; isotopes have different numbers of neutrons.
- Electrons
  - Negatively charged particles.
  - Orbit the nucleus in electron shells.
  - Determine chemical behavior and bonding of the atom.
Atomic Number (Z)
- Number of protons in the nucleus.
- Defines the identity of an element (e.g., Z = 6 for carbon).
Mass Number (A)
- Total number of protons and neutrons in the nucleus.
- A = Z + N (N = number of neutrons).
Isotopes
- Atoms of the same element with different mass numbers due to varying numbers of neutrons (e.g., Carbon-12, Carbon-14).
Electron Configuration
- Arrangement of electrons in an atom.
- Electrons occupy energy levels/shells around the nucleus (1st shell = 2 electrons, 2nd shell = 8 electrons).
- Follow the Aufbau principle, Pauli exclusion principle, and Hund's rule.
Valence Electrons
- Electrons in the outermost shell.
- Important for chemical bonding and reactivity.
Ions
- Charged atoms formed by the loss or gain of electrons.
  - Cations: Positively charged (loss of electrons).
  - Anions: Negatively charged (gain of electrons).
Atomic Models
- Dalton's Model: Atoms as indivisible particles.
- Thomson's Model: Discovery of electrons (plum pudding model).
- Rutherford's Model: Nucleus discovery, atom mostly empty space.
- Bohr Model: Electrons in fixed orbits around the nucleus.
- Quantum Mechanical Model: Electrons in probabilistic orbitals rather than fixed paths.
Periodic Table
- Organized by increasing atomic number.
- Groups (columns) indicate similar properties; periods (rows) indicate energy levels.
- Metals, nonmetals, and metalloids categorize elements.
Key Terms
- Nucleus: Central core of the atom, containing protons and neutrons.
- Electron Shells: Energy levels where electrons reside.
- Quantum Numbers: Describe electron positions and energy levels.

Atomic Structure

Matter consists of atoms, the fundamental building blocks of elements.

Subatomic Particles

Atoms are made up of protons, neutrons, and electrons.

Protons

Positively charged particles found in the nucleus.
Determine the atomic number (Z) and the identity of an element.

Neutrons

Neutral particles, also located in the nucleus.
Contribute to an atom's mass; variations create isotopes.

Electrons

Negatively charged particles that orbit the nucleus in defined electron shells.
Responsible for an atom's chemical behavior and bonding properties.

Atomic Number (Z)

Defined as the number of protons in an atom's nucleus.
Identifies the element; for example, a carbon atom has Z = 6.

Mass Number (A)

Calculated as the total number of protons and neutrons in an atom's nucleus.
Formula: A = Z + N, where N represents the number of neutrons.

Isotopes

Atoms of the same element differing in mass number due to variations in neutron count, e.g., Carbon-12 vs. Carbon-14.

Electron Configuration

Refers to the arrangement of electrons around the nucleus.
Electrons occupy shells, with 2 in the first shell and 8 in the second, following the Aufbau principle, Pauli exclusion, and Hund's rule.

Valence Electrons

Electrons located in an atom's outermost shell.
Critical for determining an element's chemical reactivity and bonding capabilities.

Ions

Charged particles formed through the loss or gain of electrons.

Cations

Positively charged ions created by the loss of electrons.

Anions

Negatively charged ions formed by the gain of electrons.

Atomic Models

Dalton's Model: Atoms as indivisible units.
Thomson's Model: Introduced electrons with the plum pudding model.
Rutherford's Model: Discovered the nucleus and established that atoms mostly comprise empty space.
Bohr Model: Proposed that electrons exist in fixed orbits around the nucleus.
Quantum Mechanical Model: Describes electrons occupying probabilistic orbitals, rather than fixed paths.

Periodic Table

Organized by increasing atomic number.
Groups (columns) reflect similar properties, while periods (rows) indicate energy levels.
Elements categorized as metals, nonmetals, or metalloids.

Key Terms

Nucleus: The atom's core containing protons and neutrons.
Electron Shells: Energy levels where electrons are positioned.
Quantum Numbers: Values that provide information on electron locations and energy levels.