Chemistry - Periodic table ( Classification of Elements)

Explore atomic structure, including nucleus and shells, and define atomic number Z and atomic mass A, showing how protons and neutrons set mass while electrons have negligible mass.

Isotopes are atoms of the same element with the same atomic number but different atomic masses due to varying neutrons, as carbon-12, carbon-13, carbon-14 and hydrogen isotopes illustrate.

Discover ionization energy, the energy to remove an outer electron, why this endothermic process carries a positive sign, and how it increases across a period and decreases down a group.

Explore electron affinity as the energy change when a neutral atom gains an electron, forming an anion, with halogens showing the highest exothermic, negative energy change.

Learn valency and valence electrons by examining how the outermost shell determines bonding potential, using sodium's 2-8-1 configuration to illustrate a valency of 1.

Explore Dobereiner’s triad model, grouping elements into triads with a middle element equal to half the sum of the outer masses, though only three triads were found.

Explore Newlands' law of octaves, classifying elements by ascending atomic mass and grouping similar properties, while examining its limitations and historical reception.

Mendeleev organized the known elements by increasing atomic mass into columns called groups, creating the periodic table whose columns contain elements with similar chemical and physical properties.

Mendeleev organized elements into groups by properties and arranged them by atomic mass while predicting undiscovered elements via gaps, such as eka-boron and eka-silicon.

Explore the limitations of Mendeleev's periodic table, including hydrogen's placement, isotopes with ascending atomic mass and their distortions, and the uncertainty in discovering new elements.

Explore the modern periodic table, arranged by atomic number rather than mass, and see how electron configuration and the metals–nonmetals division determine element properties across 18 groups and seven periods.

Contrast mendeleev's and modern periodic tables by ascending atomic mass vs atomic number, and summarize differences in groups and periods, inert gases, transition elements, and lanthanides and actinides placement.

Explore how periods and groups structure the modern periodic table, noting seven periods and 18 groups, with outermost electron counts defining groups and atomic numbers increasing across periods.

Explore the seven periods and eighteen groups of the periodic table, from short first periods to long sixth periods with lanthanides, to an incomplete seventh period of radioactive transhumanism elements.

Explore how groups in the periodic table are classified from alkali metals to noble gases, including transition and inner transition metals, with emphasis on valence electrons and outermost electrons.

Explore atomic radius trends across a period and down a group, define atomic radius and diameter, and explain how electron–nucleus attraction and outer-shell changes govern size in nanometers.

Explore how atomic radius shapes ionization energy and electron affinity, driving increased nonmetallic character across a period and stronger metallic character down a group.

Observe how valence electrons increase from left to right across a period, from one to eight in the outermost shell. Across a group, valence electrons stay the same.

Compare metals and non-metals by examining their physical properties: appearance, conductivity, malleability, density, ductility, and sonority, with emphasis on melting and boiling points at room temperature.

Compare metals and nonmetals by electropositive and electronegative properties. Metals form basic oxides and release hydrogen gas with water and acids, while nonmetals form acidic oxides and are less reactive.