atomic radius

(noun)

A measure of the size of an atom. Assuming atoms have a spherical shape, the radius of the sphere describes the size of the atom.

Related Terms

Examples of atomic radius in the following topics:

  • Atomic Radius

    • The atomic radius is one such characteristic that trends across a period and down a group of the periodic table.
    • Depending on context, the term atomic radius may apply only to isolated atoms, or also to atoms in condensed matter, covalently bound in molecules, or in ionized and excited states.
    • Under some definitions, the value of a radius may depend on the atom's state and context.
    • The way atomic radius varies with increasing atomic number can be explained by the arrangement of electrons in shells of fixed capacity.
    • A chart showing the atomic radius relative to the atomic number of the elements.

  • Atomic Size

    • The atomic radius of a chemical element is a measure of the size of its atoms.
    • These trends in atomic radii (as well as trends in various other chemical and physical properties of the elements) can be explained by considering the structure of the atom.
    • an increase in atomic size because of additional repulsions between electrons,
    • In a noble gas, the outermost level is completely filled; therefore, the additional electron that the following alkali metal (Group I) possesses will go into the next principal energy level, accounting for the increase in the atomic radius.
    • Therefore, atomic size, or radius, increases as one moves down a group in the periodic table.

  • General Trends in Chemical Properties

    • Specifically, elements are presented by increasing atomic number.
    • Elements in the same group show patterns in atomic radius, ionization energy, and electronegativity.
    • Elements in the same period show trends in atomic radius, ionization energy, electron affinity, and electronegativity.
    • Moving left to right across a period, from the alkali metals to the noble gases, atomic radius usually decreases.
    • The decrease in atomic radius also causes ionization energy to increase from left to right across a period: the more tightly bound an element is, the more energy is required to remove an electron.

  • Bond Lengths

    • The covalent radius of an atom is determined by halving the bond distance between two identical atoms.
    • Based on data for the H2 molecule, the covalent radius of H is 37 pm.
    • Generally, when we consider a bond between a given atom and a varying atomic bonding partner, the bond length decreases across a period in the periodic table, and increases down a group.
    • This trend is identical to that of the atomic radius.
    • A bond between two atoms can be thought of as a spring with two balls attached to it.

  • Ionic Radius

    • Ionic radius (rion) is the radius of an ion, regardless of whether it is an anion or a cation.
    • When an atom loses an electron to form a cation, the lost electron no longer contributes to shielding the other electrons from the charge of the nucleus; consequently, the other electrons are more strongly attracted to the nucleus, and the radius of the atom gets smaller.
    • Similarly, when an electron is added to an atom, forming an anion, the added electron repels other electrons, resulting in an increase in the size of the atom.
    • Relative sizes of atoms and ions.
    • Identify the general trends of the ionic radius size for the periodic table.

  • Percent Ionic Character and Bond Angle

    • When two elements form an ionic compound, is an electron really lost by one atom and transferred to the other?
    • The average radius of the neutral Li atom is about 2.52Å.
    • If this Li atom reacts with an F atom to form LiF, what is the average distance between the Li nucleus and the electron it has "lost" to the fluorine atom?
    • A bond angle forms between three atoms across at least two bonds.
    • This means that atoms will sit in positions that minimize the amount of space they occupy (like a salt crystal).

  • Ions

    • If an atom has the same number of protons and electrons, it is electronically neutral.
    • An ion consisting of a single atom is a monoatomic ion; an ion consisting of two or more atoms is referred to as a polyatomic ion.
    • Ionization generally involves a transfer of electrons between atoms or molecules.
    • Periodic Properties: Part 3, Ionic Radius, Predicting Ionic Charges - YouTube
    • A continuation of the discussion of periodic properties, including ionic radius and how to predict ionic charges.

  • Description of the Hydrogen Atom

    • The principal quantum number in hydrogen is related to the atom's total energy.
    • The energy levels of hydrogen are given by solving the Schrödinger equation for the one-electron atom:
    • This constant is often used in atomic physics in the form of the Rydberg unit of energy:
    • It shows a diameter about twice the radius indicated by the Bohr model.
    • Identify the unique features of the hydrogen atom that make it important for calculations in quantum mechanics

  • The Effect of the Finite Volume

    • In this approximation, the gas molecules are considered hard spheres with a defined radius (r) that cannot overlap with the radius of a neighboring particle.
    • where NA is Avogadro's number and r is the radius of the molecule.
    • Here, the size of helium atoms relative to their spacing is shown to scale under 1,950 atmospheres of pressure.

  • The Bohr Model

    • In atomic physics, the Bohr model depicts an atom as a small, positively charged nucleus surrounded by electrons.
    • Although revolutionary at the time, the Bohr model is a relatively primitive model of the hydrogen atom compared to the valence shell atom.
    • The lowest value of n is 1; this gives a smallest possible orbital radius of 0.0529 nm, known as the Bohr radius.
    • The Rutherford–Bohr model of the hydrogen atom.
    • Behavior of Electrons: Part 3, The Bohr Model of the Atom - YouTube