# Why chromium resists the effect of atmosphere

> Chromium is chemically active, yet resists air: the oxide that forms on its surface has a larger volume than the metal atoms it came from, so it forms a continuous non-porous layer that blocks further reaction with oxygen.

> [ar-EG] الـ chromium عنصر نشيط كيميائيًا، ومع ذلك بيقاوم الهوا: الـ oxide اللي بيتكوّن على سطحه حجمه أكبر من حجم ذرات الـ metal اللي اتكوّن منها، فبيعمل طبقة متصلة non-porous بتمنع إن الـ oxygen يكمّل تفاعل معاه. المطلوب: إنك تقدر تدّي السبب ده (give reasons)، وتقارنه بطبقة porous (زي الـ rust) بتسيب الـ corrosion يكمّل.

Part of: Transition Elements (https://yaani.ai/en/learn/chemistry/chem-s3-en.ch1)

## Builds on

- Chemical activity series of metals
- Rusting and corrosion
- Economic importance of vanadium and chromium

## Common mix-ups

- Chromium resists air because it is an unreactive metal.: No. Chromium is a chemically active metal. It resists the air because the oxide formed on its surface has a larger volume than the metal atoms, making a non-porous layer that stops further reaction with oxygen. ([ar-EG] لأ، الـ chromium metal نشيط فعلًا؛ اللي بيحميه هو طبقة الـ oxide اللي على سطحه.)
- Any oxide layer protects a metal.: Not any layer. Chromium's oxide has a larger volume than the metal atoms it came from, so it forms a continuous non-porous layer that stops oxygen from reaching the metal. A porous layer, like rust, lets the reaction continue underneath. ([ar-EG] مش أي طبقة؛ الطبقة الـ non-porous تحديدًا هي اللي بتحمي.)

Source: https://yaani.ai/en/concept/te.chromium-oxide-layer