Atomic Structure Overview

Atomic Structure Overview

• Atoms are the fundamental building blocks of matter, composed of protons, neutrons, and electrons.
• Protons and neutrons are located in the nucleus, the atom's positively charged core.
• Electrons orbit the nucleus in specific energy levels or shells.
• The number of protons in an atom defines its atomic number and identifies the element.
• Atoms of the same element with differing neutron counts are called isotopes.
• Atomic mass is the sum of protons and neutrons in an atom's nucleus.
• Atoms typically strive for a stable electron configuration by gaining, losing, or sharing electrons with other atoms to form chemical bonds.

Subatomic Particles

• Protons: Positively charged particles within the nucleus; mass approximately 1 atomic mass unit (amu).
• The number of protons defines the element.
• Neutrons: Neutrally charged particles within the nucleus; mass approximately 1 amu, slightly greater than a proton's.
• The number of neutrons varies among isotopes of the same element.
• Electrons: Negatively charged particles orbiting the nucleus in specific energy levels (shells); mass is much less than protons or neutrons.
• Electrons dictate an atom's chemical properties.
• Electron shells are labeled with principal quantum numbers (e.g., n=1, n=2, n=3...).

Atomic Number and Mass Number

• Atomic Number (Z): Number of protons in an atom's nucleus; uniquely identifies each element.
• Example: Carbon has an atomic number of 6, meaning 6 protons.
• Mass Number (A): Sum of protons and neutrons in an atom's nucleus; approximate atomic mass. Note: approximation due to presence of electrons.
• Example: A carbon-12 atom has atomic number 6 and mass number 12 (meaning 6 neutrons).

Isotopes

• Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.
• They possess identical chemical behavior (react similarly) but exhibit slight variations in physical properties (mass, reactivity).
• Example: Carbon isotopes include carbon-12, carbon-13, and carbon-14.

Electronic Structure

• Electrons occupy specific energy levels (shells) surrounding the nucleus.
• Shells have increasing energy levels.
• Each shell can hold a maximum number of electrons (2n^2, where n = shell number).
• Electron arrangement critically affects chemical behavior.

Shells and Subshells

• The shell model shows electrons orbiting in discrete shells.
• Reality also has subshells (s, p, d, f) within each shell where electrons reside.
• Each subshell has a specific shape and energy level.
• This substructure is essential for understanding chemical bonding.