Periodic trends cca

C BLOCK:Arrange yourselves in some

Organizational Manner

Periodic TrendsAtomic radius, Ionization energy,

Electronegativity

Elements are arranged side by side in order of increasing atomic number – makes it possible to see commonalities among them.

Vertical – Groups/Columns of the periodic table

Horizontal – Periods/Rows of the periodic table

The periodic table contains vertical and horizontal trends

Atomic Radius

The atomic radius is one-half of the distance between the nuclei of two atoms of the same element when the atoms are joined.

Trends in atomic radius

Atomic Radius Increases Down a group◦ Greater energy levels and orbitals surrounding

nucleus◦ Outer electrons are further away from nucleus◦ Shielding effect occurs as we go down the group◦ Shielding effect: The reduction of attractive force

between a nucleus and its outer electrons due to blocking effect of inner electrons

Atomic Radius Down a Group

Atomic Radius Decreases across a period Energy level stays the same

◦ No shielding changes happen◦ Increase in # of protons, therefore positive charge

increases◦ Pulls valence electrons closer

Atomic Radius Across a Period

Comparision

Down a group Across a period

Atomic number increases

Energy level (orbitals) increases

Shielding occurs Decrease nuclear

charge Radius increases

Atomic number increases

Same Energy level , no shielding

Increase in nuclear charge,

Pulls electrons in tight and decrease radius

An ion ◦is an atom or group of atoms that has a positive or negative charge

◦Cations An ion with a positive charge Metals

◦Anions An ion with a negative charge Nonmetals

IONS

◦The energy required to remove an electron from an atom is called ionization energy.

Ionization Energy

ionization energy is high,◦ takes a lot of energy to remove the outermost

electron ionization energy is low,

◦ takes only a small amount of energy to remove the outermost electron.

Smaller atomic radius, what do you think the IE is? Why?◦ High IE, small radius, high nuclear charge

therefore holding valence electrons tight

When…

Ionization energies can help you predict what ions an element will form.

◦ It is relatively easy to remove one electron from a Group 1A metal atom, but it is difficult to remove a second electron.

◦ This difference indicates that Group 1A metals tend to form ions with a 1+ charge

Trends of Ionization Energy

Energy generally increases

Energ

y g

en

era

lly

decr

ease

s

The ability of an atom to attract and hold an extra electron

- Measured as the energy change that occurs when an electron is added to an atom

- When an atom gains an extra electron it becomes negative

- Electron affinity can be either a positive or negative numerical value

- Negative Value: atom releases energy when it gains an electron

- Positive Value: atom must absorb energy for the electron to be added

Electron Affinity

Becomes More negative as we move from left to right across a period

Explained by nuclear charge, atomic radius and shielding effects

As we move down the groups, electron affinity becomes less negative

Electron Affinity Trends

◦ Electronegativity

the ability of an atom of an element to attract electrons when the atom is in a compound.

The least electronegative element in the table is cesium, with an electronegativity of 0.7.

It has the least tendency to attract electrons.

When it reacts, it tends to lose electrons and form cations.

Least Electronegative Element

The most electronegative element is fluorine, with a value of 4.0.

fluorine has such a strong tendency to attract electrons

when it is bonded to any other element it either attracts the shared electrons or forms an anion.

Most Electronegative

In general, electronegativity values decrease from top to bottom within a group. For representative elements, the values tend to increase from left to right across a period.Metals at the far left of the periodic table have low

values.

By contrast, nonmetals at the far right (excluding noble gases) have high values.

Values among transition metals are not as regular.