Periodic TrendsPeriodic Trends

Chapter 6Chapter 6

Section 3Section 3

Atomic radiusAtomic radius

Electron clouds do not have clearly defined Electron clouds do not have clearly defined edges. edges.

Atomic size is defined by how closely an atom Atomic size is defined by how closely an atom lies to a neighboring atom.lies to a neighboring atom.

Trends within periodsTrends within periods

In general, there is a decrease in atomic radii In general, there is a decrease in atomic radii as you move left-to-right across a period.as you move left-to-right across a period.

It’s caused by an increasing positive charge in It’s caused by an increasing positive charge in the nucleus and the fact that the principal the nucleus and the fact that the principal energy level within a period remains the same.energy level within a period remains the same.

Increased nuclear charge pulls outermost eIncreased nuclear charge pulls outermost e -- closer.closer.

Trends within groupsTrends within groups

Atomic radii generally increase as you move Atomic radii generally increase as you move down a group.down a group.

The nuclear charge increases and eThe nuclear charge increases and e -- are added are added to successively higher principal energy levels.to successively higher principal energy levels.

Inner eInner e-- orbitals shield outer e orbitals shield outer e--..

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Ionic RadiusIonic Radius

An An ionion is an atom or a bonded group of atoms is an atom or a bonded group of atoms that ha a positive or negative charge.that ha a positive or negative charge.

When atoms lose e- and form positively When atoms lose e- and form positively charged ions, they always become smaller.charged ions, they always become smaller.

NaNa NaNa++

Ionic Radius (cont.)Ionic Radius (cont.)

When atoms gain e- and form negatively When atoms gain e- and form negatively charged ions, they always become larger.charged ions, they always become larger.

SS SS2-2-

Trends within periods and groupsTrends within periods and groups

Elements on the left side form cations and Elements on the left side form cations and elements on the right form anions.elements on the right form anions.

As you move from left-to-right, the ionic As you move from left-to-right, the ionic radius decreases.radius decreases.

As you move down a group, there is a gradual As you move down a group, there is a gradual increase in ionic size.increase in ionic size.

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Ionization EnergyIonization Energy

Ionization energyIonization energy is defined as the energy is defined as the energy required to remove an erequired to remove an e-- from a gaseous atom. from a gaseous atom.

The loss of an electron results in an ion.The loss of an electron results in an ion.

It’s an indication of how strongly an atom’s It’s an indication of how strongly an atom’s nucleus holds onto its valence enucleus holds onto its valence e--..

Ionization Energy (cont.)Ionization Energy (cont.) After removing the 1After removing the 1stst e-, it is possible to e-, it is possible to

remove additional e-. (First ionization energy)remove additional e-. (First ionization energy)

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Trends within periodsTrends within periods

First ionization energies generally increase as First ionization energies generally increase as you move from left-to-right across a period.you move from left-to-right across a period.

Increased nuclear charge has an increased hold Increased nuclear charge has an increased hold on valence e-.on valence e-.

Related to atomic radius decrease.Related to atomic radius decrease.

Trends within groupsTrends within groups

First ionization energies generally decrease as First ionization energies generally decrease as you move down a group.you move down a group.

Valence e- are farther from the nucleus Valence e- are farther from the nucleus because atomic radius increases.because atomic radius increases.

The octet rule states that atoms tend to gain, The octet rule states that atoms tend to gain, lose or share e- in order to acquire a full set of lose or share e- in order to acquire a full set of eight valence e-.eight valence e-.

ElectronegativityElectronegativity

The The electronegativityelectronegativity of an element indicates of an element indicates the relative ability of its atoms to attract e- in a the relative ability of its atoms to attract e- in a chemical bond.chemical bond.

F is the most electronegative element.F is the most electronegative element.

Electronegativity generally decreases as you Electronegativity generally decreases as you move down a group and increases as you move down a group and increases as you move left-to-right across a period.move left-to-right across a period.

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