Chemistry: The Periodic Table Explained

The Periodic Table: Atomic Number & Groups

• The atomic number of an element is determined by the number of protons in its atoms.
• The periodic table organizes elements into groups, which are vertical columns.
• Groups indicate the number of valence shell electrons in an element's atom.

History of the Periodic Table

• Dobereiner (1817): Grouped elements into triads based on atomic mass and similar properties.
• Newlands (1863): Proposed the "Law of Octaves," suggesting similar properties occur every eight elements when arranged by atomic mass.
• Mendeleev and Meyer (1869): Independently developed the first periodic table, arranged by increasing atomic mass.
• Moseley (1913): Arranged the table by increasing atomic number, based on X-ray experiments, establishing the modern periodic table.

Periodic Table Blocks:

• s-block: Includes Group 1 (alkali metals) and Group 2 (alkaline earth metals), with electron configurations of ns1 and ns2 respectively.
• p-block: Encompasses Groups 13 to 18.
• d-block: Found in the center of the periodic table, containing Groups 3 to 12. Characterized by filling of inner d orbitals.
• f-block: Includes the two rows of elements at the bottom, the lanthanoids (Ce - Lu) and actinoids (Th - Lr). These elements are known as inner-transition elements due to the filling of f-orbitals.

Hydrogen Bonding:

• Intermolecular hydrogen bonding: Occurs between different molecules of the same or different compounds. Examples: water, alcohol, and ammonia.
• Intramolecular hydrogen bonding: Occurs within a single molecule. Examples: o-nitrophenol.

Significance of Hydrogen Bonding:

• Slow evaporation of water
• Flexibility of muscles
• Water retention in soil
• Enhanced solubility of substances
• Effectiveness of drugs
• Strength of cement concrete
• Elasticity of nylon polymer

Mole Concept:

• Mole: Unit of measurement for the amount of a substance, containing as many particles as there are atoms in 12g of the carbon-12 isotope.
• Molar mass: Mass of one mole of a substance expressed in grams.
• Mole fraction: Ratio of the moles of a component to the total moles in a mixture. It is unitless.

Solutions:

• Molarity (M): Number of moles of solute per liter of solution.
• Molality (m): Number of moles of solute per kilogram of solvent.
• Normality (N): Number of equivalents of solute per liter of solution.

Solid Structures:

• Ionic solids: Composed of positively and negatively charged ions.
• Network solids: Characterized by a continuous network of atoms held together by covalent bonds.
• Mica: A two-dimensional network solid containing one silicon atom bonded to three oxygen atoms and one monovalent atom, forming a stable molecule with a planar shape.
• Quartz: A three-dimensional network solid with one silicon atom bonded to four oxygen atoms, creating a stable molecule with a tetrahedral shape and a high melting point.

Crystallization of Inorganic Salts:

• Process: Heat a solution, evaporate solvent, cool the solution, collect and dry crystals, filter undissolved solids.
• Factors affecting crystal size: Cooling rate (faster cooling results in smaller crystals, slower cooling in larger crystals).

Checking Your Knowledge:

• Ionic radius: Be2+ is smaller than O2-.
• Electron affinity: Generally increases across a period.
• Electronegativity: Caesium (Cs) has the lowest electronegativity.
• Coordinate covalent bond: One atom provides both electrons in the bond.
• Arrangement of atoms: Zinc (Zn) is not from the same category as gold (Au), silver (Ag), and copper (Cu). They are all transition metals, but zinc is not a noble metal.