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