Periodic Table & Periodicity Ms Piela Durfee High
Feb 23, 2016
Periodic Table & PeriodicityMs Piela
Durfee High
Periodic Trends/ Periodicity A periodic trend is a pattern observed
on the periodic table for an atomic property
Each of the four trends have explanations for their group trend and their period trend
The 4 Main Periodic Trends are:
Atomic Radius
Ionization Energy
Electronegativity
Electron Affinity
The Period Trend Explanation
When comparing elements in the same period, compare the effective nuclear charges (Zeff) Effective nuclear charge is the net positive
charge experienced by electrons in an atom
The Period Trend Explanation
The atoms on the right of the periodic table have higher effective nuclear charges (Zeff) when compared to elements on the left This is due to electrons being added to the same
energy level. They are approximately the same distance away from the nucleus
In general, the further atoms are away from the nucleus, the less attracted they become
The Group Trend Explanation
When comparing atoms in the same group, compare the amount of electron shielding occuring Electron shielding is where core electrons
shield outer electrons from the charge of the nucleus
Thus, outer electrons are held less tightly because of electron/electron repulsion
The Group Trend Explanation Atoms on the top of the periodic table have less
electron shielding than atoms at the bottom As you increase in the number of energy levels, more electron shielding
occurs This does NOT occur across a period as energy levels will not change
Atomic Radius
Atomic Radius is a measure of the size of the atom Measured by the distance from the nucleus to the outermost
electrons
Atomic Radius
Atomic Radii decreases moving across a period, and increases going down a group For the period trend: with effective nuclear charge,
the increased positive charge pulls electrons closer, causing the size to decrease
With the group trend, the increasing energy levels provide more electrons, which increase the size of the atom (electron shielding doesn’t really work)
Ionization Energy
Ionization energy is the energy required to remove an electron from an atom Amount of energy increases as the number of
ionizations occur (i.e. first ionization takes less energy than the second, and so on)
Ionization Energy
Ionization energy increases going across a period and decrease going down a group With increasing effective nuclear charge, electrons
are held more tightly, thus atoms on the right require more energy to remove an electron
With increasing electron shielding, electrons are held less tightly and thus decrease in IE
Graph of IE Periodic Trend
Electronegativity
Electronegativity is the ability of an atom in a molecule to attract shared electrons to itself Think of electronegativity as a “tug of war”
Electronegativity
Electronegativity increases going across a period, and decreases going down a group Due to increasing effective nuclear charge, atoms on
the right hold electrons more tightly, causing them to have high EN
Due to electron shielding, atoms on thebottom tend to hold electrons more loosely, making them have low EN
Electronegativity
The noble gases are excluded from this trend as they tend not to bond with other atoms
This makes fluorine the most electronegative atom
Electron Affinity
Electron Affinity is the energy associated with the addition of an electron to an atom The more negative the quantity, the more
energy is released upon the addition of an electron
Electron Affinity
Electron affinity increases across a period and decreases going down a group Due to increasing effective nuclear charge, atoms on
the right tend to want to attract negative electrons more
Due to electron shielding, atoms on the bottom tend to hold electrons more loosely, making them have low EA