# Elements, compounds and mixtures

> Chemically combined, or just mixed?


## Objectives

- Tell an element, a compound and a mixture apart.
- State that a compound has a fixed ratio and new properties.
- State that a mixture keeps the properties of its parts and is separated by physical means.

## 1. Elements, compounds and mixtures: from zero




## 2. Mixed or combined?

Predict: can the magnet still pull the iron out of the black solid?

- Only after the black solid is dissolved in water
- Yes: the iron is still there, so the magnet still works
- No: iron and sulphur are now chemically joined in a new substance ✓

The magnet can no longer pull the iron out: heating joined iron and sulphur chemically into a new substance, iron(II) sulphide, FeS, with its own properties.

[ar-EG] المغناطيس مش هيقدر يسحب الـ iron تاني: التسخين خلّى الـ iron والـ sulphur يتحدوا كيميائيًا ويكوّنوا مادة جديدة، الـ iron(II) sulphide، FeS، ليها properties خاصة بيها.
## 3. A compound is a new substance

An element has one kind of atom, like Fe or S. Compound A substance formed of two or more elements chemically combined in a fixed ratio. A compound has new properties. FeS is black: not grey like iron, not yellow like sulphur. It always has 1 Fe for 1 S.


## 4. A mixture is just mixed

Mixture Two or more substances mixed physically. Each keeps its own properties, and they can be separated by physical means. A mixture and a compound are the same thing.


## 5. Element, compound or mixture?

A rock contains the compound $\ce{Fe2O3}$ with sand spread through it. How is the whole rock best described?

- A mixture: the $\ce{Fe2O3}$ and the sand each keep their properties ✓
- A compound, because it contains iron and oxygen
- An element, because it is mostly iron

The whole rock is a mixture: the compound $\ce{Fe2O3}$ and the sand are not bonded to each other, each keeps its properties, and the amount of sand can vary.

[ar-EG] الصخرة كلها mixture: الـ compound $\ce{Fe2O3}$ والرمل مش مرتبطين ببعض، وكل واحد فيهم محتفظ بالـ properties بتاعته، وكمية الرمل ممكن تختلف.
## 6. Summary

**Element**: one kind of atom (Fe, S, O). **Compound**: elements chemically combined in a fixed ratio, with new properties ($\ce{FeS}$, $\ce{Fe2O3}$). **Mixture**: substances mixed physically. Each keeps its properties, and physical means separate them. Can you explain why a magnet separates iron from an iron-sulphur mixture, but not from FeS? In the mixture, iron is only mixed physically and keeps its properties, so a magnet pulls it out. In $\ce{FeS}$, iron is chemically combined with sulphur in a new substance with new properties, so the magnet cannot pull the iron out. Next: iron is found in ores: iron compounds, mostly oxides, mixed with impurities (unwanted substances).



Chapter: Transition Elements (https://yaani.ai/ar/learn/chemistry/chem-s3-en.ch1)
Source: https://yaani.ai/ar/lesson/chem-s3-en.lesson-chem.elements-compounds-mixtures