*Random extra--Week 2: size of atoms and ions, effective nuclear charge, ionization energies, and electron affinities

A cation always has [__________] electrons and the [_________] number of protons as the parent atom

A cation always has FEWER electrons and the SAME number of protons as the parent atom; it is smaller than the atom from which it is derived

How is an anion formed?

An anion (negative ion) is formed by the addition of one or more electrons to the valence shell of an atom. This results in a greater repulsion among the electrons and a decrease in Zeff per electron. Both effects (the increased number of electrons and the decreased Zeff) cause the radius of an anion to be larger than that of the parent atom

As electrons are removed from the outer valence shell, the remaining core electrons occupying smaller shells experience a [___________] effective nuclear charge Zeff (as discussed) and are drawn [________] to the nucleus.

As electrons are removed from the outer valence shell, the remaining core electrons occupying smaller shells experience a GREATER effective nuclear charge Zeff (as discussed) and are drawn even CLOSER to the nucleus.

Core electrons are ________ at shielding, while electrons in the same valence shell _________ nuclear attraction

Core electrons are good at shielding, while electrons in the same valence shell do not block the nuclear attraction experienced by each other as efficiently.

isoelectronic atoms or ions

For atoms or ions that are isoelectronic, the number of protons determines the size. The greater the nuclear charge, the smaller the radius in a series of isoelectronic ions and atoms.

For larger atoms, the most loosely bound electron is located [______] from the nucleus and so is [_______] to remove. How does this affect ionization energy?

For larger atoms, the most loosely bound electron is located FARTHER from the nucleus and so is EASIER to remove. Thus, as size (atomic radius) increases, the ionization energy should decrease.

Ionic radius

Ionic radius is the measure used to describe the size of an ion.

Trends with cations as we move down the periodic table

Proceeding down the groups of the periodic table, we find that cations of successive elements with the same charge generally have larger radii, corresponding to an increase in the principal quantum number, n. BECAUSE Cations with larger charges are smaller than cations with smaller charges

covalent radius trends throughout the periodic table

STUDY IMAGE Trends: - covalent radius DECREASES as you move ACROSS table. (This might seem counterintuitive because it implies that atoms with more electrons have a smaller atomic radius....move onto next slide to understand). - covalent radius INCREASES as you move DOWN table.

successive ionization energies for one element always [_________]

Successive ionization energies for one element always INCREASE. There is a large increase in the ionization energies for each element. This jump corresponds to removal of the core electrons, which are harder to remove than the valence electrons.

TRUE/FALSE is removing an electron from a cation with a higher positive charge more difficult than removing an electron from an ion with a lower charge?

TRUE Removing an electron from a cation with a higher positive charge IS more difficult than removing an electron from an ion with a lower charge.

Is removing an electron from a cation is more difficult than removing an electron from a neutral atom?

TRUE Removing an electron from a cation is more difficult than removing an electron from a neutral atom because of the greater electrostatic attraction to the cation.

TRUE/FALSE it becomes easier to add an electron across a series of atoms as the effective nuclear charge of the atoms increases.

TRUE it DOES becomes easier to add an electron across a series of atoms as the effective nuclear charge of the atoms increases.

The [________] pull experienced by electrons on the right side of the periodic table draws them [________] to the nucleus, making the covalent radii [________].

The STRONGER pull (higher effective nuclear charge) experienced by electrons on the right side of the periodic table draws them CLOSER to the nucleus, making the covalent radii SMALLER. Thus, as we would expect, the outermost or valence electrons are easiest to remove because they have the highest energies, are shielded more, and are farthest from the nucleus.

Ionization Energy (IE)

The amount of energy required to remove the most loosely bound electron from a gaseous atom in its ground state. ionization processes are endothermic and IE values are always positive.

Exceptions for when electron affinity does NOT tend to become more negative moving left to right across a table

The exceptions found among the elements of group 2 (2A), group 15 (5A), and group 18 (8A) can be understood based on the electronic structure of these groups. The noble gases, group 18 (8A), have a completely filled shell and the incoming electron must be added to a higher n level, which is more difficult to do. Group 2 (2A) has a filled ns subshell, and so the next electron added goes into the higher energy np, so, again, the observed EA value is not as the trend would predict. Finally, group 15 (5A) has a half-filled np subshell and the next electron must be paired with an existing np electron. In all of these cases, the initial relative stability of the electron configuration disrupts the trend in EA.

covalent radius (purpose, definition, explanation)

Used to find the definite size of an atom. covalent radius: defined as one-half the distance between the nuclei of two identical atoms when they are joined by a covalent bond (this measurement is possible because atoms within molecules still retain much of their atomic identity). Explanation: we know as we move DOWN a group, the quantum number, n, increases by one. Thus, the electrons are being added to a region of space that is increasingly distant from the nucleus. Consequently, the size of the atom (and its covalent radius) must increase as we increase the distance of the outermost electrons from the nucleus.

Within a period, the IE generally increases with [__________] Z. Down a group, the IE value generally decreases with [________] Z

Within a period, the IE generally INCREASES with INCREASES Z. Down a group, the IE value generally DECREASES with INCREASING Z

as we move down a group, the metallic character of the atoms ____________ (increase/decrease)?

as we move down a group, the metallic character of the atoms INCREASE

each time we move from one element to the next across a period, Z [__________], but the shielding [____________] What trend does this arise?

each time we move from one element to the next across a period, Z INCREASES BY ONE, but the shielding INCREASE only SLIGHTLY. Thus, Zeff INCREASES as we move from left to right across a period.

isoelectronic

having the same number of electrons ex, Atoms and ions that have the same electron configuration are said to be isoelectronic

negative values of EA are associated with

negative values of EA means that energy is released when the gaseous atom accepts an electron. However, for some elements, energy is required for the atom to become negatively charged and the value of their EA is positive.

Aufbau principle

states that each electron occupies the lowest energy orbital available (view image)

effective nuclear charge (Zeff)

the actual nuclear charge experienced by an electron, defined as the charge of the nucleus plus the charge of the shielding electrons. Another definition" the pull exerted on a specific electron by the nucleus, taking into account any electron-electron repulsions.

Shielding (definition and how is it determined)

the effect on an electron of repulsion by electrons in lower-energy orbitals that screen it from the full effects of nuclear charge (image best describes this concept) - Shielding is determined by the probability of another electron being between the electron of interest and the nucleus, as well as by the electron-electron repulsions the electron of interest encounters.

electron affinity + trends

the energy change for the process of adding an electron to a gaseous atom to form an anion (negative ion). This process can be either endothermic or exothermic, depending on the element. TRENDS: - as we go from left to right across a period, EAs tend to become more negative. - as we move down a group, we see that the second element in the group most often has the greatest EA.

ionization energy trends across period and down group

we would expect first ionization energies to decrease down a group and to increase across a period.