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John Dalton

Proposed the first modern Atomic Theory in 1803 by combining research with known laws.

Döbereiner

Organized known elements into triads in 1829, noting that the middle element had properties between the other two.

Newlands

Introduced the concept of Octaves in 1865, grouping elements into sets of 8 with repeating properties.

Mendeleev

Created the first modern Periodic Table between 1869-1871, arranging elements by properties despite irregular mass orders.

J.J

Discovered electrons through Cathode Ray Tube experiments in 1897.

Rutherford

Discovered the nucleus via the Gold Foil Experiment in 1911.

Henry Moseley

Determined atomic numbers using x-ray spectroscopy in 1913, establishing a relationship between x-ray frequencies and atomic numbers.

Modern Periodic Table

Organized by periods (rows) and groups (columns), with a "Stair-Step" line dividing metals and nonmetals.

Metals

Typically solid, good conductors of heat and electricity, lustrous, malleable, and ductile; can form alloys.

Metalloids

All solids, less conductive than metals, can be shiny or dull, some are malleable and ductile, but tend to be brittle.

Nonmetals

Can exist as solids, liquids, or gases, poor conductors of heat and electricity (except graphite), dull appearance, and brittle.

Families

Groups of elements with similar properties in the periodic table.

Main Group Elements

Located in the s and p blocks, exhibiting predictable patterns in properties across periods and within groups.

Valence Electrons

Determine the chemical behavior of elements in the periodic table.