Periodic Law and Trends in Atomic Properties

Flashcards covering the patterns and principles of the periodic table, including Periodic Law, electronic arrangement, shielding, and the Five main trends: Atomic Radius, Ionic Radius, Ionization Energy, Electron Affinity, and Electronegativity.

Periodic Law (Mendeleev's discovery)

Discovered in 1869, this law states that when elements are arranged in order of increasing atomic mass, elements with similar properties repeat at regular intervals.

Modern Periodic Law

The principle that the chemical and physical properties of the elements repeat in a regular, periodic pattern when they are arranged according to their atomic number.

Valence electrons

The electrons located in the outermost shell of an atom where most chemical reactions occur.

Shielding

A phenomenon where inner full shells of electrons act as barriers that decrease the attraction of the protons in the nucleus for the electrons in the outer shells.

Effective nuclear charge

The net force experienced by an electron in an atom as a result of the positively charged nucleus.

Reactivity

How likely or vigorously an atom is to react with other substances, based on how easily electrons can be removed or how strongly they attract electrons from other atoms.

Metal Reactivity Trend

Reactivity increases down a group and to the left of the periodic table because larger atoms have lower attractive forces, making it easier to lose electrons.

Non-metal Reactivity Trend

Reactivity increases up a group and to the right of the periodic table because smaller atoms have higher attractive forces, allowing them to attract electrons more strongly.

Atomic Radius (AR)

The distance from the nucleus to the outermost electrons, typically expressed in picometres $(pm)$.

Atomic Radius Periodic Trend

Decreases from left to right across a period as the number of protons increases, causing a stronger pull on electrons toward the nucleus.

Atomic Radius Group Trend

Increases moving down a group because each atom adds another energy level (shell).

Cation

A positive ion produced by removing electrons; it is smaller than its neutral atom due to increased nuclear pull per electron and decreased electron-electron repulsion.

Anion

A negative ion produced by gaining electrons; it is larger than its neutral state because the effective nuclear charge is shared among more electrons and electron-electron repulsion increases.

Ionization Energy (IE)

The amount of energy required to remove an electron from an atom or ion in the gaseous state, measured in $kJ/mol$ and represented by the equation: $X + \text{energy} \rightarrow X^+ + e^-$.

1st Ionization Energy

The amount of energy required to remove one electron from the outer energy level of a neutral atom.

2nd Ionization Energy

The amount of energy required to remove a second electron from a charged atom; it is always greater than the 1st ionization energy.

Electron Affinity (EA)

The change in energy that occurs when an electron is added to the valence energy level of an atom.

Negative Electron Affinity Value

Indicates that energy is released when an atom gains an electron; the more negative the value, the more easily the atom gains an electron.

Positive Electron Affinity Value

Indicates that energy is absorbed when an atom gains an electron; the more positive the value, the harder it is for the atom to gain an electron.

Electronegativity (EN)

A measure of an atom’s ability to "hog" or attract electrons that are shared between two atoms in a molecule.

Electronegativity Trends

Values increase across a period (left to right) and decrease down a group.