Atomic Structure and Shells

Core Principles of Matter and Atomic Structure

• All matter is composed of fundamental building blocks known as atoms.
• An atom consists of two main regions: a central core called the nucleus and surrounding energy levels referred to as electron shells.
• Protons and neutrons are subatomic particles located exclusively inside the nucleus.
• Electrons are subatomic particles that orbit the nucleus within specific electron shells.
• The group number of an element on the periodic table indicates the number of electrons present in its outermost electron shell (the valence shell).

Subatomic Particles and Their Properties

• Proton:

  • Charge Nature: Positive
  • Relative Charge: $+1$
  • Relative Mass: $1$
  • Location: Inside the nucleus

• Neutron:

  • Charge Nature: Neutral
  • Relative Charge: $0$
  • Relative Mass: $1$
  • Location: Inside the nucleus

• Electron:

  • Charge Nature: Negative
  • Relative Charge: $-1$
  • Relative Mass: Very small
  • Location: Outer shells surrounding the nucleus

Representing and Drawing Atoms

• Isotopic Notation and Notation Components:

  • Element Symbol: Chemical symbol representing the element (e.g., $\text{Na}$ for Sodium).
  • Mass Number: The total number of protons and neutrons in the nucleus (written as a superscript to the left of the chemical symbol, e.g., $23$
  • Atomic Number: The total number of protons in the nucleus (written as a subscript to the left of the chemical symbol, e.g., $11$

• Fundamental Equations:

  • $\text{Mass Number} = \text{Protons} + \text{Neutrons}$
  • $\text{Atomic Number} = \text{Protons} = \text{Electrons}\text{ (in a neutral atom)}$

• Electron Shell Rules and Capacity:

  • Electron shells are filled in order from the innermost shell closest to the nucleus moving outward.
  • Standard maximum shell capacity progression: $(2, 8, 8)$
  • Inner (1st) shell maximum capacity: $2$ electrons
  • Middle (2nd) shell maximum capacity: $8$ electrons
  • Outer (3rd) shell maximum capacity: $8$ electrons

• Worked Example — Sodium ($\text{Na}$):

  • Symbol Representation: $\mathbf{^{23}_{11}Na}$
  • Mass Number: $23$
  • Atomic Number: $11$
  • Number of Protons: $11$
  • Number of Electrons: $11$
  • Number of Neutrons: $23 - 11 = 12$
  • Electron Configuration Breakdown:
  • 1st Shell: $2$ electrons
  • 2nd Shell: $8$ electrons
  • 3rd Shell (outermost): $1$ electron
  • Electronic Configuration Notation: $2, 8, 1$
  • Group Placement: Since there is $1$ electron in the outer shell, sodium is located in Group 1.