Chapter 9

rare gas notation

An alternate way of writing an electron configuration is to write the rare gas symbol(noble gas) that immediately precedes the element in brackets and then continue the rest of the electron configuration. (So potassium's and calcium's rare gas notation configurations would be: K: [Ar]4s1; Ca: [Ar]4s2)

Sometimes the actual configuration doesn't match with what is predicted. We already mentioned the anomalous f-block's starting element. We predict that the 4f orbital should begin with Lanthanum, since lanthanum's electron configuration is predicted to be [Xe]6s2 4f1. But the 4f orbital actually begins with cerium, because experimental evidence has shown that lanthanum's electron configuration is [Xe]6s2 5d1. This is called

Anomalous Electron Configurations

Aufbau Principle

Electrons are believed to fill the orbitals around a nucleus in order of increasing energy

what is the highest shell (n)?

It is the first number in the electron configuration, the 1 in the 1s, or the 4 in the 4p.

When an atom is converted to a cation - it loses electrons and becomes positively charged. The radius ___, because the nucleus ___.

decreases; pulls the electrons in more closely

Atomic radius is the

distance between the nucleus and the outer cloud of electrons.

Trends in atomic radius is opposite the trends for ionization energy and __

electron affinity

Ionization energy (IE) is the

energy required to remove an electron from an atom or an ion in its gaseous state.

Electron affinity (EA) is the

enthalpy change that occurs when an electron is added to a gaseous atom.

The elements of group 2A and 5A already have a filled or a half-filled orbital, so they don't want to ___ to mess that up. This is why their electron affinities are less favorable.

gain an electron

There are two exceptions to this ionization energy trend between elements in group 2A and 3A, and the second is between elements in group 5A and 6A. These deviations have to do with these elements electron configurations. While eight valence electrons is the most stable configuration for most elements, ___ or completely ___ orbitals are also stable. They are more stable than other partially filled orbitals.

half-filled; filled

When an atom is converted to an anion - it gains electrons and becomes negatively charged. The radius ___, because the ____.

increases; nucleus has less pull and the electrons are pushed further out

The atomic radius increases as you go down the periodic table. This is because not only are you ____, these electrons are going into higher n levels. The valence shell increases from period to period. So therefore the atomic radius will increase.

increasing the number of electrons and protons

In each of the cases where the ionization energy sharply increases, this is when the ion is losing its ___. For example, sodium (Na) has one valence electron - so after it loses this valence electrons, you are taking electrons from its __, this is why it takes so much more energy to take the second electron from sodium.

inner electrons; inner core

When the actual values of atomic radius are available, one can do a relative comparison by using the lower left and upper right corners as reference points. The closer a element is to francium, the ___ it is. The closer an element is to helium, the ___ it is.

larger; smaller

From the IE table we can see the trends in ionization energy as well. It increases as we go across from ___, and also ___ as we go from bottom to top. This is the opposite of the atomic radius trend that we learned in the previous part. For lithium (Li) to get a rare gas configuration, it only has to lose one valence electron, so it make sense that its first ionization energy is the ___ in that period. It also seems natural that it would take ___ energy to remove electrons from atoms as they move closer to having a rare gas configuration. Since a rare gas already has that configuration, it makes sense that it would have the highest in that period.

left to right; increases; lowest; more

The octet rule states that

most main group elements want to have 8 electrons in their outermost shell. (Hence why the name "octet rule" as octet equals 8.)

In 1925, Austrian physicist Wolfgang Pauli discovered a fundamental rule for electron arrangement, the Pauli Exclusion Principle, which says that

no two electrons can have the same four quantum numbers (This means that only TWO electrons can occupy an orbital!)

For atoms of main group elements, the valance electrons are the

number of electrons in the highest shell (n) of its electron configuration.

When most main group elements form ions to form ionic compounds or become covalent compounds they want to obtain this "magic" configuration of these group 8A elements (that make them stable) of eight valence electrons. This is known as the

octet rule.

Throughout the history of modern chemistry, the most common way to visualize atoms has been as spheres. A common way to measure the size of a sphere is it ___, which is the distance from the center of the sphere to the outer edge. ___ is often used to describe the size of atoms for this reason.

radius; Atomic radius

Atomic radius increases from ___ on the periodic table, because as you add more electrons to the same group, the radius does not decrease as you would expect. This is because you are adding electrons to the same group, and the number of ___ is increasing. The increase in _____ charge will pull electrons closer to the nucleus.

right to left (or decreases from left to right); protons; positive

Now look at the main group elements (the A groups), and how it is split across the transition metals: with two groups to the left, and six groups to the right. These are the maximum number of electrons that the ___ and __ subshells can hold. For the transition metals in the middle - there are ten columns or groups, the maximum that the ___ subshells can hold. And the inner transition metals (the lanthanide and actinide series) have 14 groups, the same number that the ___ subshell can hold.

s and p; d; f

Hund's rule states that

the most stable electron arrangement is the one with the most parallel spins (the same value of ms). It means that electrons don't like to pair up - if they don't have too.

The only element that does not follow the octet rule is Hydrogen - when it bonds to other atoms, it will only want ___ electrons - so it follows the ___ rule!

two; duet

Valence electrons are

used by an atom in chemical bonding.

Adding two more electrons does not increase the radius, because

we are also adding two more protons.

isoelectronic

when atoms and ions that have the same number of electrons. (Both Na+ and O2- have the same number of electrons as neon, 10 electrons.)

pseudo-rare gas configuration which is a

which is a rare gas configuration [Rare gas] plus a filled d orbital or a filled d and filled f orbital for atoms that are in the 6th or 7th period. ([Rare gas] nd10 or [Rare gas] (n-1)f14 nd10)