Atomic Structure & Electric Charge

Introduction

Everything electrical starts at the atomic level. To understand electricity, we must first understand the atom—the building block of all matter. The behavior of electrons within atoms determines whether a material conducts electricity or insulates against it.

In this lesson, we'll explore the atomic structure, learn about electric charge, and understand why some materials allow electric current to flow while others resist it.

The Structure of the Atom

An atom is the smallest unit of matter that retains the properties of an element. Atoms consist of three main particles:

Subatomic Particles

Electric Charge

Electric charge is a fundamental property of matter. It comes in two varieties: positive and negative. Like charges repel each other, while opposite charges attract.

Charged Objects

Objects become charged through the transfer of electrons:

• Positively Charged: When an atom loses electrons (more protons than electrons)
• Negatively Charged: When an atom gains electrons (more electrons than protons)
• Neutral: Equal number of protons and electrons

Coulomb's Law

The force between two charged particles is given by Coulomb's Law:

Where:

• F = Force in Newtons (N)
• k = Coulomb's constant (8.99 × 10⁹ N·m²/C²)
• q₁, q₂ = Charges in Coulombs (C)
• r = Distance between charges in meters (m)

Conductors, Semiconductors, and Insulators

Materials are classified by how easily electrons can move through them:

Conductors

Materials with free electrons that can move easily. Examples include:

• Copper (most common conductor)
• Aluminum
• Silver (best conductor)
• Gold (corrosion-resistant)

Insulators

Materials that hold electrons tightly, preventing current flow:

• Rubber
• Plastic (PVC)
• Glass
• Ceramic
• Dry air

Semiconductors

Materials whose conductivity can be controlled:

• Silicon (most common)
• Germanium
• Gallium Arsenide

How Electric Current Flows

When we connect a voltage source (like a battery) to a conductor, we create an electric field that pushes free electrons through the material.

Conventional Current vs Electron Flow

There are two ways to describe current flow:

• Electron Flow: Electrons move from negative to positive terminal
• Conventional Current: Positive charge "flows" from positive to negative

Current Formula

Current is the rate of charge flow:

Where:

• I = Current in Amperes (A)
• Q = Charge in Coulombs (C)
• t = Time in seconds (s)

Example Calculation

// Calculate the current when 10 Coulombs of charge
// flows through a conductor in 2 seconds

const charge = 10;    // Q = 10 C
const time = 2;       // t = 2 s

const current = charge / time;  // I = 5 A

console.log(`Current = ${current} Amperes`);

If 6.242 × 10¹⁸ electrons flow past a point in 1 second, that's 1 Ampere of current!

Practice Problems

// Number of electrons = Total charge / Elementary charge
const elementaryCharge = 1.602e-19;  // 1.602 × 10⁻¹⁹ C
const totalCharge = 1;               // 1 C

const numElectrons = totalCharge / elementaryCharge;
console.log(`Number of electrons = ${numElectrons.toExponential(3)}`);
console.log(`= 6.242 × 10¹⁸ electrons`);

const charge = 50;   // Q = 50 C
const time = 10;      // t = 10 s

const current = charge / time;
console.log(`Current = ${current} A`);

const k = 8.99e9;      // Coulomb's constant
const q1 = 2e-6;        // 2 µC = 2 × 10⁻⁶ C
const q2 = -3e-6;       // -3 µC = -3 × 10⁻⁶ C
const r = 0.1;          // 0.1 m

const force = k * (Math.abs(q1 * q2)) / (r * r);
console.log(`Force = ${force.toFixed(2)} N`);

Summary

• Atoms consist of protons (positive), neutrons (neutral), and electrons (negative)
• Electric charge is quantized in units of the elementary charge e = 1.602 × 10⁻¹⁹ C
• Like charges repel, opposite charges attract
• Conductors have free electrons; insulators tightly bound electrons
• Semiconductors have conductivity that can be controlled
• Current I = Q/t (Charge divided by time)