Bell Work

• Which element is more electronegative?Br or I?

• Which element has a higher ionization energy?Mg or Ca?

• Which element is more reactive? O or Se?

• *All worksheets are due now.

Practice

Physical Science – Lecture 63

Periodic Trends

Summary of Periodic Table Trends

Moving Left --> Right • Atomic Radius Decreases • Ionization Energy Increases • Electronegativity Increases

Moving Top --> Bottom • Atomic Radius Increases • Ionization Energy Decreases • Electronegativity Decreases

Atomic radius

• The atomic radius is the distance from the atomic nucleus to the outermost stable electron orbital in an atom.

Trend - Period

• The atomic radius tends to decrease as one progresses across a period because the growing positive charge of the nucleus pulls the electrons closer.

Trend - Group

• The atomic radius usually increases while going down a group due to the addition of a new energy level (shell).

• This new layer of electrons makes the radius larger.

• The pull of the protons in the nucleus is not as strong because the electrons are farther from the nucleus.

Atomic Radius

Ionization Energy

• The ionization potential (or the ionization energy) is the minimum energy required to remove one electron from each atom in a mole of atoms in the gaseous state.

Ionization Energy

• Ionization energy is governed by the charge on the nucleus, the amount of screening by the inner electrons, the distance between the outer electrons and the nucleus.

Trend - Period

• Trend-wise, ionization potentials tend to increase across a period because the greater number of protons (higher nuclear charge) attract the orbiting electrons more strongly, thereby increasing the energy required to remove one of the electrons.

Trend - Group

• Down a group, the ionization energy will decrease, since the valence electrons are farther away from the nucleus and experience a weaker attraction to the nucleus's positive charge.

Second Ionization

• The second ionization energy is the energy required to remove a second valence electron.

Successive Ionization Trends

• Successive ionization energies increase. The second ionization energy is always greater than the first ionization energy, the third is always greater than the second, etc.

Electron Affinity

• The electron affinity is a measure of the attraction between the incoming electron and the nucleus. The higher the attraction, the higher the electron affinity.

Trend - Period

• As one progresses from left to right across a period, the electron affinity will increase, due to the larger attraction from the nucleus, and the atom "wanting" the electron more as it reaches maximum stability.

Trend - Group

• Down a group, the electron affinity decreases because of a large increase in the atomic radius, electron-electron repulsion and the shielding effect of inner electrons against the valence electrons of the atom.

Electron Affinity

• As the atom gets bigger, the incoming electron is further from the nucleus and so feels less attraction. The electron affinity therefore falls as you go down the Group.

Fluorine not in the Trend

• In the case of fluorine, because the atom is very small, the existing electron density is very high. That means that the extra repulsion is particularly great and lessens the attraction from the nucleus enough to lower the electron affinity below that of chlorine.

Electronegativity

• Electronegativity is a measure of the ability of an atom or molecule to attract pairs of electrons in the context of a chemical bond.

Trend - Period

• Trend-wise, as one moves from left to right across a period in the periodic table, the electronegativity increases due to the stronger attraction that the atoms obtain as the nuclear charge increases.

Trend - Group

• Moving down a group, the electronegativity decreases due to the longer distance between the nucleus and the valence electron shell, thereby decreasing the attraction, making the atom have less of an attraction for electrons or protons.