Section 6-3

Section 6.3 Periodic Trends

• Compare period and group trends of several properties.

principal energy level: the major energy level of an atom

ion

ionization energy

octet rule

electronegativity

• Relate period and group trends in atomic radii to electron configuration.

Trends among elements in the periodic table include their size and their ability to lose or attract electrons

Factors that influence Periodic Trends• Shielding - core electrons block the

attraction between the nucleus and the valence electrons.

• Nuclear Charge – The number of protons in the nucleus will impact the attraction of valence electrons

•Across a given period (row) nuclear charge will have a greater influence than shielding

•Down a given group (column) Shielding will have a greater influence than nuclear charge

Section 6-3

Atomic Radius• Atomic size is a periodic trend influenced

by electron configuration and nuclear charge.

• For Metals, atomic radius is half the distance between adjacent nuclei in a crystal of the element.

• For elements that occur as molecules, the atomic radius is half the distance between nuclei of identical atoms.

Section 6-3

Atomic Radius (cont.)

1

2

3

4 5

6

7

• Atomic Radius– Increases to the LEFT and DOWN

Atomic Radius

• Why larger going down?

– Higher energy levels have larger orbitals

– Shielding - core e- block the attraction between the nucleus and the valence e-

• Why smaller to the right?

– Increased nuclear charge without additional shielding pulls e- in tighter

Atomic Radius

Atomic Radius (cont.)

Section 6-3

Atomic Radius (cont.)

Section 6-3

Ionic Radius

• An ion is an atom or bonded group of atoms with a positive or negative charge.

• When atoms lose electrons and form positively charged ions, they always become smaller for two reasons:

1. The loss of a valence electron can leave an empty outer orbital resulting in a small radius.

2. Electrostatic repulsion decreases allowing the electrons to be pulled closer to the radius.

Section 6-3

Ionic Radius (cont.)

• When atoms gain electrons, they can become larger, because the addition of an electron increases electrostatic repulsion.

Section 6-3

Ionic Radius (cont.)

• The ionic radii of positive ions generally decrease from left to right.

• The ionic radii of negative ions generally decrease from left to right, beginning with group 15 or 16.

Section 6-3

Ionic Radius (cont.)

• Both positive and negative ions increase in size moving down a group.

Section 6-3

Ionization Energy• Ionization energy is defined as the energy

required to remove an electron from a gaseous atom.

• The energy required to remove the first electron is called the first ionization energy.

Section 6-3

Ionization Energy (cont.)

• Why opposite of atomic radius?

– In small atoms, e- are close to the nucleus where the attraction is stronger

Why small jumps within each group?

– Stable e- configurations don’t want to lose electrons (p1 and p4) lose p1 leaves s2; lose p4 leaves p3

– S sublevel slightly shields the P sublevel

– The 4th electron in enter into a P sublevel will have to pair up with an electron, thus it experiences more repulsion

Ionization Energy

Ionization Energy (cont.)

Section 6-3

Ionization Energy (cont.)

• Removing the second electron requires more energy, and is called the second ionization energy.

• Each successive ionization requires more energy, but it is not a steady increase.

Section 6-3

Ionization Energy (cont.)

• The ionization at which the large increase in energy occurs is related to the number of valence electrons.

• First ionization energy increases from left to right across a period.

• First ionization energy decreases down a group because atomic size increases and less energy is required to remove an electron farther from the nucleus.

– Al 1st I.E. 577 kJ

2nd I.E. 1,815 kJ

3rd I.E. 2,740 kJ

Core e- 4th I.E. 11,600 kJ

• Successive Ionization Energies

– Large jump in I.E. occurs when a CORE e- is removed.

Ionization Energy

Ionization Energy (cont.)

Section 6-3

Ionization Energy (cont.)

Section 6-3

Ionization Energy (cont.)

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

• The octet rule is useful for predicting what types of ions an element is likely to form.

Section 6-3

Ionization Energy (cont.)

• The electronegativity of an element indicates its relative ability to attract electrons in a chemical bond.

• Electronegativity decreases down a group and increases left to right across a period.

•Melting points of elements tend to increase in the middle of a period (row) and will decrease at each end of a given row.•Melting points tend to increase as you go down a given group

Section 6-3

Electronegativity

A. A

B. B

C. C

D. D

Section 6-3

A B C D

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Section 6.3 Assessment

The lowest ionization energy is the ____.

A. first

B. second

C. third

D. fourth

A. A

B. B

C. C

D. D

Section 6-3

Section 6.3 Assessment

A B C D

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The ionic radius of a negative ion becomes larger when:

A. moving up a group

B. moving right to left across period

C. moving down a group

D. the ion loses electrons