# Crystal Structure

When a crystal grows in a **constant **environment, the form develops as if identical blocks were added continuously.

Crystal Structure = Lattice Point + **Basis**

Basis = single atom OR group of atoms attached to each lattice point

**Lattice points in 3D**

- Lattice points are infinitesimal points in space.
- Atoms are physical objects.
- Number, composition and arrangement of atoms is the same for each lattice point.

**Unit cell**

A **lattice point **can be described by a **vector T **with**lattice lengths**: the axial length u_{1}, u_{2}, and u_{3}.

**Unit Cell =** small portion of any given crystal that can be used to **reproduce **the crystal

Three lattice vectors (a, b, and c, originating from one corner of the unit cell) describe the size and shape of the unit cell vectors.

**Lattice angles:**the inter-axial angles α, β and γ**Lattice constants:**All of the parameters of the unit cell.**Volume:**

**3D Bravais Lattice Types**

Only 14 **unique **Bravais Lattices (unit cells) to fill space with a periodic arrangement of points.

**Each**lattice point is decorated with the**same**collection of atoms.- Most elemental metals (about 90 %) crystallize into three densely packed crystal structures: bcc, fcc and hcp.

Note: The empty circles refers to the lattice points and not the atoms. You can put any group and size of atoms at these points.