diff --git a/docs/sch3uz.md b/docs/sch3uz.md
index 2fffe1f..3e0c8f7 100644
--- a/docs/sch3uz.md
+++ b/docs/sch3uz.md
@@ -397,13 +397,13 @@ Orbitals of the same type but in higher energy levels are simply larger, so any
*f*-orbitals have more complex shapes. There are 7 in each energy level starting from $n=4$.
-Orbitals are filled up in order of increasing energy, which is shown in the image below.
+The **Aufbau principle** states that orbitals are filled up in order of increasing energy, which is shown in the image below.
(Source: Kognity)
-As such, the orbitals are filled in the order shown in the arrow below:
+### Orbital box diagrams
-
(Source: Kognity)
+According to **Hund's rule**, atoms fill all orbitals in the same sublevel before pairing up, similar to *Monopoly* house-building rules.
## 3 - Periodicity