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)

• sheilding

• 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

• across a period, atomic radius __________ because ___________

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 __________ because ___________

increases 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

Why Exceptions for atomic radius happen

• a new subshell (s, p, d, f) is added to the outermost energy level; instead of decreasing, it increases

• Exceptions for atomic radius

• Mg—>Al

  • [Ne]s2—>[Ne]3s2,3p1

• Zn—>Ga

  • [Ar] 4s2,3d10—>[Ar] 4s2,3d10, 4p1

• across a period, ionization energy ___________ because ___________

increases because 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 __________ because ____________

decreases because 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

why exceptions for ionization energy happe

• when 1 orbital is full or half full, it is more stable and harder for an electron to be removed, making it decrease

• exceptions for ionization energy

• Be—>B

• Mg—>Al

• N→O

• P—>S

• Across a period, electronegativity ___________ because ___________

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

• down a group, electronegativity _______ because ____________

decreases because 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

why exceptions happen for electronegativity

• electrons aren’t necessary because an atom is already stable with a full outer shell

exceptions for electronegativity

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