Understanding Chemical Bonds and the Periodic Table

Metals and Non-Metals Comparison

History of the Periodic Table

Mendeleev published the periodic table based on the principle that chemical elements vary periodically with their atomic mass. Other historical contributions include Newlands' Law of Octaves and Döbereiner's Triads.

The Modern Periodic Table

The current periodic table contains 117 elements, including metals, non-metals, metalloids, and noble gases, grouped in rows and columns. These elements are characterized by their metallic character and reactivity, and they are abbreviated by symbols.

Unions Between Atoms and the Octet Rule

Elements come together to stabilize, acquiring the electron configuration of the nearest noble gas (8 electrons in their last layer, known as the octet rule). This forms bonds, which are the electrostatic forces that bind atoms. There are three main types of bonds:

Covalent Bonds

A covalent bond is formed by sharing electrons between non-metals. It can give rise to two structures:

• Molecules: These contain a small number of atoms. We can represent them using the Lewis diagram. Properties include low melting and boiling points, low densities, and poor conductivity.
• Crystals: These consist of a large number of atoms.

Ionic Bonds

Ionic bonds are formed by electrostatic attractions between cations and anions. They are formed by the transfer of electrons between metals and non-metals. Properties: They are crystalline solids at room temperature, soluble in water, and electrically conductive when dissolved.

Metallic Bonds

A metallic bond is a chemical bond that holds the atoms of metals together. These atoms are grouped very close to each other, resulting in very compact structures.

Chemical Formulas and Molecular Mass

The chemical formula of a substance expresses the type and number of constituent atoms. The total molecular mass is the sum of the atomic masses of the atoms that form it. Its unit is the atomic mass unit (u).

Centesimal Composition: This is the percentage of the elements that form a compound.

The Mole and Molar Calculations

A mole is the amount of substance that contains as many particles as there are atoms in 12 g of carbon-12. Its symbol is mol. It is the amount of substance that contains 6.022 x 10²³ particles.

Molar Mass: This is the mass of one mole of particles. It is represented by M and its unit is g/mol or kg/mol.

The formula for the amount of substance is: n (amount of substance) = / M

Molarity

Molarity is the amount of substance per liter of solution, symbolized by M.