Periodic Trends

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Effective Nuclear Charge Noun

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[uh-fek-tiv noo-klee-er charj]

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Effective Nuclear Charge

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The net positive charge experienced by an electron in a multi-electron atom, accounting for the shielding effect of inner-shell electrons.

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Example: This diagram shows that an outer electron is pulled toward the nucleus (attraction) but is also pushed away by other electrons (repulsion), which reduces the overall pull it feels.

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Valence Electrons Noun

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[vey-luhns ih-lek-trons]

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Valence Electrons

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The electrons located in the outermost electron shell of an atom, which are the electrons involved in forming chemical bonds.

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Example: This Bohr model of a Sodium atom shows its electrons in shells. The single electron in the outermost shell is the valence electron.

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Atomic Radius Noun

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[uh-tom-ik rey-dee-uhs]

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Atomic Radius

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A measure of an atom's size, typically defined as one-half the distance between the nuclei of two identical bonded atoms.

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Example: This diagram shows that atomic radius increases as you move down a group (family) and decreases as you move across a period in the periodic table.

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Picometer Noun

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[pee-koh-mee-ter]

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Picometer

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A unit of length equal to one trillionth of a meter, commonly used for measuring atomic and molecular distances.

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Example: The image shows the atomic radius of a Helium atom is 140 picometers (pm), visually defining this tiny unit of length used for atoms.

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Ion Noun

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[ahy-on]

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Ion

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An atom or molecule that has a net electrical charge due to the loss or gain of one or more electrons.

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Example: A neutral sodium atom loses its single outer electron to become a stable, positively charged sodium ion (Na⁺) with a full outer electron shell.

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Cation Noun

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[kat-ahy-on]

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Cation

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A positively charged ion that is formed when a neutral atom loses one or more of its valence electrons.

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Example: A neutral sodium atom loses its single valence electron, resulting in more protons than electrons and creating a positively charged ion called a cation (Na+).

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Anion Noun

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[an-ahy-on]

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Anion

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A negatively charged ion that is formed when a neutral atom gains one or more electrons in its valence shell.

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Example: A neutral chlorine atom gains an electron to fill its outer shell, becoming a negatively charged chloride ion (anion) with a stable configuration.

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Ionization Energy Noun

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[ahy-uh-nuh-zey-shuhn en-er-jee]

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Ionization Energy

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The minimum energy required to remove the most loosely bound electron from a neutral gaseous atom in its ground state.

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Example: This diagram shows that ionization energy is the energy needed to remove an electron from the outer shell of an atom.

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Coulomb's Law Noun

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[koo-loms law]

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Coulomb's Law

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A law stating the electrostatic force between two charged particles is proportional to the product of their charges and inversely proportional to the square of the distance between them.

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Example: This diagram shows that the attractive force between a positive nucleus and a negative electron gets stronger with more charge and weaker with more distance.

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First Ionization Energy Noun

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[furst ahy-uh-nuh-zey-shuhn en-er-jee]

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First Ionization Energy

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The specific amount of energy required to remove the first, or outermost, electron from a neutral atom in the gaseous state.

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Example: This image shows that first ionization energy is the energy needed to overcome the nucleus's attraction and remove the outermost electron from a neutral atom.