---
title: "Simple Cubic Packing | Inorganic Chemistry II"
description: "Simple cubic packing is a crystal structure with atoms at cube corners, 6 coordination, and 52% packing efficiency in Inorganic Chemistry II solids."
canonical: "https://fiveable.me/inorganic-chemistry-ii/key-terms/simple-cubic-packing"
type: "key-term"
subject: "Inorganic Chemistry II"
unit: "Unit 6"
---

# Simple Cubic Packing | Inorganic Chemistry II

## Definition

Simple cubic packing is a crystal structure in which atoms sit at the corners of a cube. In Inorganic Chemistry II, it is a basic way to describe how atoms arrange in a solid and compare packing efficiency, coordination number, and unit-cell geometry.

## What It Is

Simple cubic packing is a crystal structure in Inorganic Chemistry II where atoms are located only at the eight corners of a cube. Because each corner atom is shared by eight neighboring cubes, one unit cell contains the equivalent of just one atom total. That makes it one of the simplest unit cells you will see in solid-state chemistry.

The geometry is easy to picture, but the packing is not very efficient. Atoms in a simple cubic lattice touch along the edges of the cube, so the edge length is equal to two atomic radii, a = 2r. The atoms do not fill the space especially well, which is why the packing efficiency is only about 52%. In other words, almost half the volume of the crystal is empty space.

The coordination number is 6, meaning each atom touches six nearest neighbors, one in each direction along the x, y, and z axes. That is lower than in close-packed structures, where atoms are surrounded by more neighbors and fit together more tightly. This lower coordination is one reason simple cubic packing is uncommon in real materials.

You will often use simple cubic packing as a reference point rather than as a common real-world model. Polonium is the classic example of an element that crystallizes in a simple cubic structure under standard conditions. Some other solids can adopt similar arrangements only under special conditions, but most metals prefer body-centered cubic or close-packed arrangements because those pack space more efficiently.

When you work with this structure, the key move is to connect the picture to the numbers. Count shared corner atoms correctly, identify the coordination number, and use the edge-to-radius relation to relate the lattice size to atomic size. That turns a cube diagram into a usable solid-state model instead of just a visual.

## Why It Matters

Simple cubic packing gives you a baseline for comparing solid structures in Inorganic Chemistry II. Once you know how much space this lattice wastes and how few neighbors each atom has, the differences between simple cubic, body-centered cubic, and close-packed arrangements become much easier to see.

It also ties directly into solid properties. Lower packing efficiency usually means less dense atomic arrangement, and coordination number affects how strongly a solid holds together at the local level. When you later study metallic bonding, lattice energy, or physical properties such as density and stability, this structure gives you a clear reference point for what a less efficient lattice looks like.

In lab or problem-solving settings, simple cubic packing shows up when you interpret unit-cell diagrams, calculate atomic radius from lattice edge length, or identify whether a crystal is likely to be simple cubic, BCC, or close packed. It trains you to read three-dimensional structures carefully instead of guessing from a flat drawing. That skill carries into X-ray diffraction, materials questions, and any section where crystal geometry matters.

## Connections

### [Unit Cell](/inorganic-chemistry-ii/key-terms/unit-cell)

Simple cubic packing is built from the unit cell, the smallest repeating chunk of a crystal lattice. In this case, the unit cell is a cube with atoms only at the corners. If you can count what is shared and what stays inside one cell, you can find the number of atoms per unit cell and compare it to other crystal structures.

### Coordination Number

The coordination number tells you how many nearest neighbors surround one atom. For simple cubic packing, that number is 6 because each atom touches neighbors along the three axes in both directions. This is a quick way to compare simple cubic with denser structures that give each atom more contacts.

### Body-Centered Cubic (BCC)

BCC is often compared with simple cubic because both use cubic unit cells, but they are not the same arrangement. BCC has an extra atom in the center of the cube, which changes the number of atoms per unit cell, the coordination number, and the packing efficiency. If you confuse them, check whether the center of the cube is occupied.

### Close-Packed Structures

Close-packed structures are the opposite end of the efficiency scale from simple cubic packing. They use staggered layers that leave less empty space and give each atom more neighbors. Comparing these structures helps you see why many metals favor dense arrangements instead of the sparse geometry of simple cubic.

## On the AP Exam

A crystal-structure problem often asks you to identify a simple cubic lattice from a cube diagram, then use the geometry to calculate atom count, coordination number, or edge length. You may also be asked to compare its packing efficiency with BCC or close-packed structures. On a quiz or problem set, the big move is to show that the corners are shared, so the unit cell contains one atom total and a = 2r. If the question gives an edge length or atomic radius, you can use that relation to solve for the other value and check whether the structure matches the drawing.

## simple cubic packing vs Body-Centered Cubic (BCC)

Simple cubic packing and BCC are both cubic crystal structures, so they get mixed up easily. The difference is that BCC has one atom in the center of the cube, while simple cubic has atoms only at the corners. That one extra atom changes the total atoms per unit cell, the coordination number, and the packing efficiency.

## Key Takeaways

- Simple cubic packing is a crystal structure with atoms only at the eight corners of a cube.
- One unit cell contains the equivalent of one atom because each corner atom is shared among eight cubes.
- The coordination number is 6, so each atom touches six nearest neighbors.
- Its packing efficiency is about 52%, which makes it much less efficient than close-packed structures.
- The edge length and atomic radius are related by a = 2r in the simple cubic model.

## FAQs

### What is simple cubic packing in Inorganic Chemistry II?

Simple cubic packing is a crystal structure where atoms sit only at the corners of a cube. In Inorganic Chemistry II, it is used to describe one of the simplest unit-cell arrangements and to compare packing efficiency, coordination number, and lattice geometry.

### How many atoms are in a simple cubic unit cell?

A simple cubic unit cell contains the equivalent of one atom. Even though there are atoms at all eight corners, each corner atom is shared by eight neighboring unit cells, so the total contribution adds up to 1.

### What is the coordination number of simple cubic packing?

The coordination number is 6. Each atom touches six neighbors, one in each direction along the three spatial axes. That is lower than in denser structures, which is one reason simple cubic packing is not very common in real solids.

### How is simple cubic different from body-centered cubic?

The main difference is location of the atoms inside the unit cell. Simple cubic has atoms only at the corners, while body-centered cubic has those corner atoms plus one atom in the center of the cube. That center atom changes the count, coordination number, and packing efficiency.

## Related Study Guides

- [6.2 Bonding in Solids](/inorganic-chemistry-ii/unit-6/bonding-solids/study-guide/oUy0CxMBfQk7omUg)

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