Protons, Neutrons, and Electrons

Mostly just explains how you should answer the long answer questions on the test

Atomic radii decrease as atomic numbers increase ACROSS a given period

More protons cause effective nuclear charge, enc, increasing the attractive force of the nucleus and therefore pulling the outer electrons closer to the nucleus resulting in a smaller atomic radius.

Atomic radii increase as atomic number increases DOWN a column or group

Increased number of occupied energy levels increases the distance between the nucleus and outer electrons. Full energy levels (inner core electrons) provide shielding between the nucleus and valence electrons, thus down a column in spite of more protons, the effective nuclear charge, ENC, is nearly constant in a column.

Ionization energy increases as atomic number increases ACROSS a given period

More protons cause greater nuclear charge, ENC, increasing the attractive force of the nucleus, and therefore holds the valence electrons more tightly, making the ionization energy tightly, making the ionization energy higher. More protons are acting on electrons in the same valence orbital. (Make sure to reference Coulomb’s Law)

Ionization energy decreases as atomic number increases DOWN a column or group

Increased number of occupied energy levels increases the distance of the valence electrons from nucleus and therefore increasing the distance over which the ENC attracts. (Make sure to reference Coulomb’s Law) Full energy levels (core electrons) block some of the nuclear force between the nucleus and valence electrons, thus within a column, and effective nuclear charge, ENC, is somewhat constant.

There will be one ionization that will be MUCH greater increase over the previous

Removing the electron that is one more than the number of valence electrons will be an entire energy level closer to the nucleus and that electron will be acted upon by a greater ENC. Do think about the number of valence electrons. Removing each successive valence electron will require a slightly larger amount of energy due to the previous removal of electrons causing less electron-electron repulsion and allowing the valence electrons to skootch close to the nucleus and thus be attracted by a slightly greater force due to the slight decrease in distance between the nucleus and the outermost electrons.

Metals are more reactive as you move down a column

Because metals react by losing electrons, a more loosely held electron will result in a more reactive metal. This is directly tied to the same reasons for ionization energy trends. With an increased number of energy levels comes increased distance from the nuclear attraction making the electron more loosely held and more available for reacting.

Non-metals are more reactive as you move up a column

Because non-metals tend to gain electrons, a strong nuclear attraction will result in a more reactive non-metal. This means that an atom with the highest ENC and the least number of energy levels should be the most reactive nonmetal (F) because the nucleus has the greatest ENC working over the shortest distance.

Positive ions are smaller than their “parent” neutral atoms

Positive metal ions result from the loss of all the valence electrons. This means the outermost electrons in a cation are now in an energy level one level closer tot he nucleus than the electrons in the original neutral atom. If the entire set of valence electrons are not removed, there will be decreased electron-electron repulsions between the remaining valence electrons allowing the valence electron cloud to contract.

Negative ions are larger than their “parent” neutral atoms

Negative nonmetal ions result from the addition of valence electrons. Increased electron-electron repulsions cause the electron cloud to expand.

Isoelectronic ions are different sizes due to the number of protons

State that the number of electrons is the same, but the number of protons is different. An increased number of protons will draw the electron cloud closer causing a smaller ion.

Electronegativity

the “pull” that one atom exerts on another atom’s electrons when in a covalent bond.

Metals

• Thermal/electrical conductors

• Malleable

• Ductile

• Metallic Luster

Tend to lose electrons when formed ions (cations)

Non-Metals

• Thermal/Electrical Insulators

• Brittle

• Dull

Metalloids

• Semi Conductors

Aufbau Principle

Electrons occupy the lowest energy orbitals first

Pauli’s Exclusion Principle

No two electrons can have the same 4 quantum numbers

• Relevance: Max 2 electrons per orbital.

• one spins up, one spins down

Hund’s Rule

When electrons fill a “sub-level”, each electron fills an orbital of equal energy before pairing up