Chemical Elements: Properties, Reactions, and Bonds

Ranking Elements

The first classification of chemical elements was based on their chemical and physical properties, dividing them into two large groups: metals and non-metals.

• The first classification was done by J.W. Döbereiner. He observed a link between the atomic mass and properties of elements such as barium, calcium, and strontium. He arranged 40 elements in a line, one after another, by their mass.
• John Newlands arranged the elements by atomic mass, from the lowest to the highest, in columns. This is now called the Law of Octaves.
• D.I. Mendeleev arranged the elements by atomic mass. As a result of this work, the periodic law of elements was discovered in 1869.

Forces Between Molecules

These are listed from weakest to strongest:

1. Dispersion forces: Occur between nonpolar molecules that are symmetrical and have an even electronic distribution.
2. Induced dipole forces: Occur between polar and nonpolar molecules.
3. Dipole-dipole forces: Attractive forces between polar molecules, which have a positive and a negative side.
4. Hydrogen bonds (H-bonds): Occur between polar molecules containing a highly electronegative atom and another atom of a different molecule.

Chemical Reactions

All pure substances are created through the reaction of chemical elements. For any substance to react, the following conditions must be met:

• Reactive particles must be activated.
• Particles must collide with the correct orientation.

When performing stoichiometric calculations, these steps must be taken into account:

• Formulate the reagents involved in the reaction and the products that are generated.
• Adjust the stoichiometric coefficients of the reaction.

In a chemical reaction, the mass of all substances involved is directly proportional to the number of moles.

n = m / M, PV = nRT (gas phase), c = n / V (in the case of dissolution)

Elements in the gas phase: H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂

Chemical Bonds

Chemical bonds are interactions between atoms, ions, or molecules that generate stable partnerships.

Smaller particles aim to achieve a lower energy level. If they do not have 8 valence electrons (octet rule), they reduce their energy to achieve it.

The valence of an element is the number of electrons that its atoms lose, gain, or share when combining with atoms of other elements.