Periodic Trends

periodicity: Trends or recurring variations in element properties with increasing atomic numbers

electronegativity: The tendency of an atom to attract electrons in a bond to itself

ionization energy: Energy required to remove an electron from a gaseous atom or ion/remove from the 1rst electron in the valence electron’s shell

Atomic Radius: One half of the distance between the nuclei of 2 identical atoms when they are joined by a covalent bond

Nuclear Charge: The pull exerted on a specific electron by the nucleus (# of protons)

across a period, atomic radius decreases

• sheilding is when another electron blocks the attraction of an additional electron to the nucleus

• effective nuclear charge: the regular amount of protons, or the nuclear charge (z), with sheilding taken into account; zeff=z-sheilding

• atomic radius decreases because the effective nuclear charge (zeff) increases while shielding remails constant (n is constant), and electrons are pulled closer by increasing atomic number/protons in the nucleus, causing more attraction and a smaller atomic radius

down a group, atomic radius increases

• this happens because there are more energy levels; the principal quantum number (n, vertical numbers) increases as energy levels are added, giving rise to a larger atomic radius

Exceptions for atomic radius happen because a new subshell (s, p, d, f) is added to the outermost energy level; instead of decreasing, it increases

• Mg—>Al

  • [Ne]s2—>[Ne]3s2,3p1

• Zn—>Ga

  • [Ar] 4s2,3d10—>[Ar] 4s2,3d10, 4p1

across a period, ionization energy increases

• the effective nuclear charge (zeff) goes up with the increasing atomic number, causing more attraction; this makes it more difficult to remove a valence a valence electron, meaning more energy will be required

down a group, ionization energy decreases

• more energy levels are present, meaning that there are more core electrons (electrons close to the center), giving rise to more sheilding; there is therefore less attraction, making it easier to remove a valence electron and causing more blockage; this blockage makes it easier to take an electron away with less energy required

exceptions for ionization energy are because when 1 orbital is full or half full, it is more stable and harder for an electron to be removed, making it decrease

• Be—>B

• Mg—>Al

• N→O

• P—>S

Across a period, electronegativity increases

• this is because there is more effective nuclear charge (zeff), meaning that it is more attractive to valence electrons

down a group, electronegativity decreases

• there are more energy levels, meaning that there are more core electrons and therefore more sheilding; there is more distrance between valence electrons and the nucleusl it is less attractive to the electrons

exceptions happen for electronegativity when electrons aren’t necessary because an atom is already stable with a full outer shell

• noble gases are already stable so they have very little electronegativity