Periodicity Unit Part 3

Periodic Law When arranged by increasing atomic number, the chemical elements display a regular and repeating pattern of chemical and physical properties.

Periodic Trends Atomic Radius Ionization Energy Electronegativity Metal Reactivity

Atomic Radius Definition One half the distance between the nuclei of two atoms of the same element when the atoms are joined

Atomic Radius Trend Left to right (across a row) the atomic radius decreases Top to bottom (down a column) the atomic radius increases

Atomic Radius Horizontal Trend Decreases from left to right The positive protons are pulling the outer negative electrons more closely to the nucleus because the nuclear charge is increasing (due to additional protons) and the outermost electrons are not being shielded from it (due to electrons being added to the same energy level)

Atomic Radius Vertical Trend Increases from top to bottom The atom is getting larger because the electrons are being added to higher principle energy levels and the outermost electrons are being shielded from the strong nuclear charge Shielding  electrons filling in the orbitals between the nucleus and outer electrons help block the attraction of the positive nucleus so outer electrons are NOT being pulled toward the nucleus

Ionization Energy Definition The energy needed to remove an electron from an atom

Ionization Energy Trend Left to right (across a row) the ionization energy increases Top to bottom (down a column) the ionization energy decreases

Ionization Energy Horizontal Trend Increases from left to right The increased nuclear charge of each successive element produces an increased hold/pull on the valence electrons This increased pull makes it more difficult for an electron to be removed and therefore requires more energy

Ionization Energy Vertical Trend Decreases from top to bottom As the size of the atom increases, nuclear charge has a smaller effect on the valence electrons (since they are further from the nucleus) Less energy is required to remove an electron from this energy level

Electronegativity Definition The ability of an atom to attract electrons when it is in a compound.

Electronegativity Trend Left to right across a row the electronegativity increases (not including the noble gases) Top to bottom down a column the electronegativity decreases

Electronegativity Horizontal Trend Increases from left to right Atoms toward the right are more inclined to gain electrons and are more likely to pull electrons toward itself in a bond

Electronegativity Vertical Trend Decreases from top to bottom There is an increased distance between the valence electrons and nucleus so the attraction of the nucleus for the bonding electrons is minimized

Metal Reactivity Definition The tendency of a metal to undergo a chemical reaction

Metal Reactivity Trend Left to right across a row the reactivity for metals decreases Top to bottom down a column the reactivity for metals increases Francium is the most reactive metal

Metal Reactivity Horizontal and Vertical Trend Horizontal Trend: Decreases left to right Metals still want to give away valence electrons but since they have more of them to get rid of, more energy is required Vertical Trend: Increases from top to bottom As go down a group, outermost electrons are further from the nucleus (less nuclear pull) so it is easier for them to be lost (requires less energy)

Alkali Metal Reactivity (down a group) odic%20Table%20e%20config/PTable_trends%20arou nd%20table.html odic%20Table%20e%20config/PTable_trends%20arou nd%20table.html

Nonmetal Reactivity Trend Reactivity decreases from top to bottom Higher up = atoms with the higher electronegativity resulting in a more vigorous exchange of electrons. Fluorine is the most reactive nonmetal! Reactivity increases from left to right the closer you get to fulling your s- and p- orbitals the more motivated you are to do so.