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Periodic Table

A table used to categorize elements based on their properties and predict how they will react.

Dmitri Mendeleev

Professor of Chemistry at St. Petersburg University who developed the periodic table in 1869 based on chemical and physical properties of elements.

Groups

Columns in the periodic table that contain elements with similar properties.

Periods

Rows in the periodic table that represent different energy levels of elements.

Alkali Metals

Group I elements in the periodic table, including lithium, sodium, potassium, rubidium, and cesium, which are highly reactive and have properties such as good heat and electricity conductivity, low density, and low melting point.

Halogens

Group VII elements in the periodic table, including fluorine, chlorine, bromine, and iodine, which become darker and change from gas to liquid to solid down the group.

Transition Elements

Elements located between Groups II and III in the periodic table, including copper, iron, nickel, and zinc, which are harder, stronger, and have higher density compared to Group I and II metals.

Noble Gases

Group VIII elements in the periodic table, including helium, neon, argon, krypton, xenon, and radon, which are colorless, monatomic gases that are very unreactive.

Valence Electrons

Electrons in the outermost energy level of an atom, which determine the chemical properties of an element.

Displacement Reactions

Reactions where a more reactive element displaces a less reactive element in a compound, such as chlorine displacing iodine in a potassium iodide solution.

Metallic Character

The tendency of an element to exhibit metallic properties, which increases from left to right in a group in the periodic table.

Giant Metallic Structure

A structure exhibited by metals in which positive metal ions are surrounded by a sea of delocalized electrons.

Giant Covalent Structure

A structure exhibited by certain elements, such as carbon in diamond or silicon dioxide, where atoms are bonded together by strong covalent bonds.

Simple Molecular Structure

A structure exhibited by non-metals, where atoms are held together by weak intermolecular forces.

Electronic Structure

The arrangement of electrons in an atom or molecule, which determines its chemical behavior.

Catalytic Activity

The ability of certain elements or compounds to speed up chemical reactions without being consumed in the process.

Fractional Distillation

A process used to separate different gases from a mixture, such as the separation of helium from other gases through the liquefaction of air.