Periodic Definitions & Trends

Table of ContentsLecture/Lab/Activity Date Pg#

14. The History of Atomic Models 9/14/10 3115. Structure of the Atom 9/15/10 3516. Isotopes 9/16/10 3717. Beanium Lab 9/17/10 18. Electron Probability Lab 9/20/10 3919. Electron Configuration 9/21/10 4120. Orbital Diagrams 9/22/10 4321. Electron Config Practice 9/23/10 4522. The Periodic Table 9/24/10 4723. Periodic Def & Trends 9/27/10 49

Objective:The student will label a periodic table to identify and explain periodic trends including atomic radius, electronegativity and ionization energy.

Agenda:The Periodic Table– Lecture

How to read the Periodic Table

6

CCarbon

12.011

Atomic Number

Elemental Symbol

Elemental Name

Atomic Mass

Definitions

• Atomic Number• Is the same as the number of protons in an element.• If this number changes the element name must change

as well.• Atomic # = # of protons = # of electrons

• Atomic Mass• Is a weighted average of all the atoms in a naturally

occurring sample of an element (mass & relative abundance)

• 1 amu – one tweflth the mass of a carbon-12 atom

Calculating Neutrons

• Round the Atomic Mass Atomic Mass

- Atomic Number

(difference = # neutrons)

6

C

Carbon

12.011

Example:

Atomic Mass = 12

Atomic # = 6

Difference = 6

Difference = # neutrons

Calculating Atomic Mass

• 3 values required:• # of stable isotopes of an element

• The mass of each isotope

• The natural percent abundance of each isotope

• ? If Element X has 2 naturally occurring isotopes, what is its atomic mass? Mass 1 = 10.012 amu and has a relative abundance of 19.91 % , Mass 2 = 11.009 amu and has a relative abundance of 80.09%

Periodic Law

• When elements are arranged in order of increasing atomic #, elements with similar properties appear at regular intervals.

0

50

100

150

200

250

0 5 10 15 20

Ato

mic

Ra

diu

s (

pm

)

Atomic Number

Chemical Reactivity

• Families• Similar valence e- within a group result in similar

chemical properties

Periodic Trends

• Atomic Radius• size of atom• Increases to the LEFT and DOWN

1

2

3

4 5

6

7

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

Periodic Trends

• First Ionization Energy• Energy required to remove one e- from a

neutral atom.• Increases going UP and to the RIGHT

1

2

3

4 5

6

7

Ionization Energy

• 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 e-

Electronegativity

• The attraction an element has on a shared paired of electrons

1

2

3

4 5

6

7

Periodic Trends

• Melting/Boiling Point• Highest in the middle of a period.

1

2

3

4 5

6

7

Ionic Radius

• Cations (+)• lose e-• smaller

• Anions (–)• gain e-• larger

© 2002 Prentice-Hall, Inc.