---
title: "Simple Cubic in Inorganic Chemistry I"
description: "Simple cubic is a crystal lattice with atoms at cube corners, one atom per unit cell, 6 neighbors, and low packing efficiency in Inorganic Chemistry I."
canonical: "https://fiveable.me/inorganic-chemistry-i/key-terms/simple-cubic"
type: "key-term"
subject: "Inorganic Chemistry I"
unit: "Unit 13"
---

# Simple Cubic in Inorganic Chemistry I

## Definition

Simple cubic is a crystal structure where atoms sit only at the corners of a cube. In Inorganic Chemistry I, it is a basic solid-state model with one atom per unit cell, coordination number 6, and low packing efficiency.

## What It Is

Simple cubic is a crystal lattice in Inorganic Chemistry I where atoms occupy only the eight corners of a cube. Because each corner atom is shared by eight neighboring cubes, the unit cell contains one whole atom total, not eight. That sharing is the first thing to get straight, because the drawing can look more crowded than the counting really is.

The geometry is easy to describe but not especially efficient. In a simple cubic array, each atom touches six nearest neighbors, one along each positive and negative axis direction. That gives a coordination number of 6, which is low compared with more tightly packed structures like body-centered cubic or face-centered cubic.

The unit cell edge length is tied directly to atomic size. In the ideal hard-sphere model, atoms at adjacent corners touch along the edge, so the cube edge length equals 2r, where r is the atomic radius. That simple relationship is useful when you are asked to find unit cell dimensions, atomic radii, or densities from a diagram or set of lattice data.

Another feature that shows up in solid-state problems is packing efficiency. Simple cubic fills only about 52% of the available space with atoms, leaving a lot of empty volume. That is one reason it is rare among real metals. When a structure uses space more efficiently, atoms usually sit in arrangements that lower overall energy and improve stability.

You will not see simple cubic very often in the wild, but it is still worth knowing because it gives you a clean baseline for crystal structure calculations. Polonium is the classic metallic example, and lithium is sometimes discussed in this context depending on how the solid is modeled. In class, the structure is often used as the simplest case for counting atoms in a unit cell, comparing packing, or introducing Miller indices and crystal planes.

## Why It Matters

Simple cubic gives you a starting point for reading and comparing crystal structures in Inorganic Chemistry I. Once you can count atoms, neighbors, and edge lengths in the simplest lattice, body-centered cubic and face-centered cubic become much easier to sort out because you can see what changes in the arrangement.

It also shows up in problems that ask you to connect structure to properties. Low packing efficiency means more empty space, which affects density and helps explain why this lattice is uncommon for metals. If you are given a diagram, you may need to infer coordination number, estimate atomic radius from the cell edge, or compare how tightly atoms are packed across different lattices.

This term also builds your visual literacy for solid-state chemistry. A lot of Inorganic Chem I work asks you to move between a 3D model, a 2D drawing, and a numerical calculation. Simple cubic is a clean place to practice that translation without extra structural features getting in the way.

## Connections

### Body-centered cubic (BCC)

BCC is a better-packed cubic lattice where atoms sit at the corners plus one atom in the center of the cube. Compared with simple cubic, it has a higher coordination number and packing efficiency, so it is a good comparison when you need to explain why simple cubic is rarely found in metals. If you can count atoms in simple cubic, BCC is the next step up in complexity.

### Face-centered cubic (FCC)

FCC places atoms at the corners and on each face of the cube, which gives much tighter packing than simple cubic. In class problems, FCC is often used as the contrast case for coordination number, density, and nearest-neighbor contact. Simple cubic helps you notice what FCC adds and why that changes the number of atoms per unit cell and the amount of empty space.

### Lattice parameters

Lattice parameters are the measurements that describe the repeating unit of a crystal, especially the edge lengths and angles. For simple cubic, the relationship is especially clean because the cube edge is directly linked to atomic radius in the hard-sphere model. That makes simple cubic a useful structure for practicing unit cell calculations and interpreting crystal dimensions.

### [Interatomic distance](/inorganic-chemistry-i/key-terms/interatomic-distance)

Interatomic distance is the spacing between neighboring atoms in a crystal, and simple cubic makes that distance easy to see along the cube edges. The nearest neighbors in this lattice sit along the axes, so the edge length becomes the key distance in many problems. That is why simple cubic often appears in questions about radius, contact, and spacing.

## On the AP Exam

A quiz question may show a cube diagram and ask you to identify the lattice, count atoms per unit cell, or calculate the coordination number. A problem set might give you the edge length and atomic radius, then ask you to use the simple cubic contact relationship to find the missing value. You may also be asked to compare simple cubic with BCC or FCC by ranking packing efficiency or explaining why one structure is more common for metals. In a lab or homework context, this term can show up when you interpret unit cell drawings, diffraction-related notes, or a table of crystal structures. The main skill is translating the picture into counts and geometry, not memorizing the name alone.

## simple cubic vs Body-centered cubic (BCC)

Simple cubic and BCC are both cubic lattices, so they can look similar at first glance. The difference is that BCC has an extra atom in the center of the cube, while simple cubic has atoms only at the corners. That extra center atom changes the number of atoms per unit cell, the coordination number, and the packing efficiency.

## Key Takeaways

- Simple cubic is a crystal structure with atoms only at the corners of a cube.
- Because each corner atom is shared, one simple cubic unit cell contains one whole atom total.
- Each atom has 6 nearest neighbors, so the coordination number is 6.
- The packing efficiency is low, about 52%, which is why the structure is uncommon for metals.
- In calculations, the cube edge length equals 2r when adjacent atoms touch along the edge.

## FAQs

### What is simple cubic in Inorganic Chemistry I?

Simple cubic is a crystal lattice where atoms sit at the eight corners of a cube. In the hard-sphere model, the atoms touch along the edges, giving one atom per unit cell and a coordination number of 6. It is a basic solid-state model used for counting, geometry, and comparison with denser lattices.

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

A simple cubic unit cell contains one whole atom. Each of the eight corner atoms is shared by eight neighboring unit cells, so the total contribution is 8 times 1/8. This is a common place where students miscount by treating each corner as a full atom.

### What is the difference between simple cubic and BCC?

Simple cubic has atoms only at the corners, while BCC has corners plus one atom in the center of the cube. That center atom raises the packing efficiency and coordination number compared with simple cubic. If a diagram shows a cube-center atom, it is not simple cubic.

### Why is simple cubic rare in metals?

It is rare because the atoms do not pack efficiently, with only about 52% of the space filled. Metals usually favor structures that let atoms pack more closely and lower the overall energy. Polonium is the classic example often used when simple cubic does appear in a real element.

## Related Study Guides

- [13.1 Crystal Systems and Bravais Lattices](/inorganic-chemistry-i/unit-13/crystal-systems-bravais-lattices/study-guide/Q5CKnYs5d6fPTJBV)

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