Electron Configuration
and Periodic Properties
Atomic Radii
-The atomic radius is half the distance between the nuclei of two identical atoms that are bonded together. An atom’s size is defined by its orbital’s edge.
-There are several period trends in the periodic table. The atomic radius decreases across a period because of the increasing positive charge of the nucleus. Electrons are pulled closer to the nucleus when they add to the s and p sublevels of the same main energy level. This results in an increase of atomic radii, so the difference in the radii becomes smaller in between neighboring atoms in each period.
-There are also group trends in the periodic table. The atomic radii increases as you go down a group. When electrons occupy sublevels in higher main energy levels that are farther away from the nucleus, the atoms’ sizes increase.
Ionization Energy
A+energy ->A++e-, where A is an atom of any element in the periodic table, and A+ is an ion of that element.
ion: an atom or group of bonded atoms with a positive or negative charge.
ionization: processes that result in the formation of ions.
ionization energy: the energy required to form a neutral atom of an element.
If there is enough energy supplied in an atom, electrons can be removed.
Electron Affinity
Period Trends
An atom’s electron affinity is the energy change that takes place when an electron is acquired by a neutral atom. Usually when an atom acquires an electron, it releases energy, but sometimes atoms are forced to gain an electron because of the energy addition.
Group Trends
Electron affinities usually become more negative across a period within the p block while electrons add the the same p sublevel of atoms with increasing nuclear charge.
-except groups 14 & 15
Adding Electrons to Negative Ions
Electron affinities don’t have regular trends within groups. As you go down a group, electrons usually become more difficult. This is because there is a slight increase in effective nuclear charge down a group, which increases electron affinities, and an increase in atomic radius down a group, which decreases electron affinities.
Valence Electrons
Valence Electrons are when electrons are available to be lost, gained, or shared in the formation of chemical compounds.
They are often located in incomplete filled main-energy levels.
Main- group elements valence electrons are located in the outermost s and p.
Group number 1 2 13 14 15 16 17 18
Valence electrons 1 2 3 4 5 6 7 8
Electronegativity
America’s most famous chemist Linus Pauling came up with a scale electronegativity which is the tendency of an atom or radical to attract electrons in the formation of an ionic bond.
Electronegativity tends to increase across each period and decrease or stay the same down a group. But there are always exceptions.
Noble gases are usually part of the exceptions because they do not form compounds.
Periodic Properties of the d- and f-Block Elements
d- block has 0 to 2 electrons and s orbital has 1 to 10 electrons in the d sublevel.
Because ns sublevel can then interact with their surroundings, electrons in the d sublevel that is incompletely filled are the ones that have the characteristic properties.
Atomic radii decreases across the periods but this is generally a lot less decrease the the main-group elements.
d-block elements can decrease slightly and then increase forming a dip because of their electron reactions.
f- block elements (period 6) have a fall in some element due to atomic number increase. The radii is not a rule following pattern and is all over the place for f- block elements.
Ionization energies of d-block and f-block elements increase across the periods.
This happens because electrons are available for ionization in the outer sublevels and are less shielded from the increasing nuclear charge in the incomplete (n-1)d sublevels.
The highest occupied sublevels always remove electrons first in d and f blocks.
d sublevels, the first electrons to be removed are in the outermost sublevels.
Most d-block elements commonly form 2+ ions in compounds.
d- block elements follow general trend for electronegativity values to increase as radii decrease.
d-block electronegativities range from 1.1 and 2.54 and f-block 1.1 to 1.5.
Ionic Radii
Positive ions are called cations and negative ions are called anions. Within a period, metals on the left tend to form cations and nonmetals on the upper right usually form anions. Cationic radii decreases across a period and anionic radii decreases across each period for elements in Groups 15-18. This is because cationic radii decrease from left to right across each period. In a group, there is an increase of ionic radii going down.