Periodic Properties of Elements

Flashcards covering key concepts and trends in the periodic table, including effective nuclear charge, atomic/ionic size, ionization energy, and electron affinity.

Effective Nuclear Charge (Z*eff)

The actual positive nuclear charge 'felt' by an electron in an atom (other than hydrogen), typically lessened by shielding electrons.

Shielding

The phenomenon where core electrons block valence electrons from experiencing the full attraction of the nucleus.

Z*eff Formula

Z - S, where Z is the atomic number (nuclear charge) and S is the number of shielding core electrons (an approximation).

Atomic Radius

Half of the experimentally determined distance between two identical neighboring nuclei in a solid (for metallic or non-metallic elements).

Atomic Size Trend (Group)

Increases from top to bottom in a group due to an increase in the principal quantum number (n) of valence electrons, with Z*eff remaining similar.

Atomic Size Trend (Period)

Decreases from left to right across a period as the effective nuclear charge (Z*eff) increases, pulling electrons closer to the nucleus within the same shell (n).

Cation

A positively charged ion formed when an atom loses one or more valence electrons.

Ionic Size (Cations vs. Parent Atom)

Cations are always smaller than their original atoms because there are more protons than electrons, resulting in a stronger pull on the remaining electrons.

Ionic Size Trend (Cations in a Group)

Increases from top to bottom for cations with the same charge, following the same trend as atom sizes because of increasing principal quantum number (n).

Ionic Size Trend (Cations in a Period)

Decreases from left to right in a period for cations with different charges (increasing positive charge), as the nuclear positive charge increases.

Isoelectronic Species

Species (atoms or ions) that have the same number of electrons.

Anion

A negatively charged ion formed when a non-metal atom gains one or more valence electrons.

Ionic Size (Anions vs. Parent Atom)

Anions are always larger than their parent atoms because there are more electrons than protons, leading to less pull toward the nucleus and increased electron-electron repulsion.

Ionic Size Trend (Anions in a Group)

Increases from top to bottom for anions with the same charge, similar to atomic size trends.

Ionization Energy (I.E.)

The energy required to remove one mole of electrons from one mole of isolated, gaseous atoms or ions. It is always an endothermic (positive) value.

First Ionization Energy (IE1)

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

Ionization Energy Trend (Period)

Generally increases from left to right across a period as the effective nuclear charge (Z*eff) increases.

Ionization Energy Trend (Group)

Generally decreases from top to bottom in a group as the principal quantum number (n) of the valence electron increases, making the electron further from the nucleus and easier to remove.

Successive Ionization Energies

The energy required to remove additional electrons after the first, with IE1 < IE2 < IE3, etc., as it requires more energy to remove an electron from a more positive ion or a core electron.

Electron Affinity (E.A.)

The heat or enthalpy absorbed or released when one mole of electrons is added to one mole of isolated, gaseous atoms or ions, reflecting an atom's desire for an electron.

Electron Affinity (∆EAH)

A measure of electron affinity; common for most elements to be exothermic (∆EAH < 0, high E.A.), though it can be endothermic (∆EAH > 0, no desire).

Electron Affinity Trend (Period)

Generally increases (becomes more negative or more exothermic) from left to right across a period as the effective nuclear charge (Z*eff) increases, leading to a greater tendency to accept an electron.

Successive Electron Affinity

Describes the energy change involved in adding multiple electrons; typically, the addition of the first electron can be exothermic, but adding an electron to an already negatively charged anion requires energy (endothermic).