1. 1 st unit of chemistry Properties of compounds depending on its chemical bond

2. Ionic compounds They are solid at room temperature. Why? The ionic bond is very strong. Atoms are joined by strong forces. They have high melting points. Why? As the ionic bond is very strong, it requires a lot of energy to separate the atoms, in order for the substance to become liquid.

3. Ionic compounds They are fragile. Why? When you hit the crystal, ions are displaced: positive charges face positive charges and negative charges face negative charges. Ions with the same charge repel each other. That´s why the crystal breaks when hit by even small forces.

4. Ionic compounds

5. They dissolve in water. Why? Electrons in the water molecule are not evenly spread. One end of the molecule is slightly negative compared to the other end. Water molecules interact with the ions, separating them from each other.

6. Ionic compounds

7. They can´t conduct electricity when they are in their solid state. Why? To conduct electricity it is necessary to have charges which can move freely. That doesn´t happen when ionic compounds are in their solid state: charges are in fixed positions in the crystal.

8. Ionic compounds They can conduct electricity when dissolved in water or melted. Why? Because when they are dissolved or melted, ions can move freely (the crystal no longer exists).

9. Covalent compounds which form a net of atoms They are solid at room temperature with high melting points. Why? The covalent bond is very strong, so it requires a lot of energy to break the net of atoms in order to transform the substance into liquid. They can´t dissolve in water. Why? As there are no ions, water doesn´t interact with the atoms.

10. Covalent compounds which form a net of atoms They don´t conduct electricity. Why? Because there are no ions. Some examples of covalent compounds (or elements) which form a net of atoms are carbon (C), which can be in the form of diamond or graphite; silica (silicon dioxide, SiO 2 ); or carborundum (silicon carbide, SiC).

11. Covalent compounds that form molecules They can be gas, liquid or solid at room temperature, but always with low boiling and melting points. Why? Covalent bond is very strong, but molecules are not joined by covalent bonds, they are joined by intermolecular forces, which are very weak.

12. Covalent compounds that form molecules Most of them don´t dissolve in water. Why? As there are no ions, water doesn´t interact with the molecules. They can´t conduct electricity. Why? There are no ions.

13. Metallic elements They are solid at room temperature, except mercury (Hg), which is a liquid. They have high melting points. Why? Metallic bond is a strong bond. Atoms are joined to each other by strong forces. It requires a lot of energy to separate these atoms (in order to transform the solid into liquid).

14. Metallic elements They can conduct electricity. Why? Because they have electrons that can move freely. They can conduct heat. Why? Because atoms, which are very close to each other, can transmit thermal vibration.

15. Metallic elements They are ductile [dúctiles] (wires can be made) and malleable [maleables] (sheets can be made). Why? The layers of atoms can move easily without changing the structure of the net of atoms.

16. Metallic elements

17. Several metals can be melted together forming alloys (aleaciones). One example is bronze=copper+tin. Why? After melting, metals can easily form a new net of atoms when cooled down. They have high density. Why? Atoms are very close to each other in the net.