Atoms and the Periodic table

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Slide 38

Chapter Outline

Models of the Atom (continued)

The Orbital Model

Orbits are replaced with orbitals, volumes of space where the electrons can be found.

The arrangement of electrons in the orbitals is the electronic configuration of an atom, which determines the chemistry of an atom.

Slide 39

Definitions

Electrons in the highest occupied energy level are the greatest stable distance from the nucleus. These outermost electrons are known as valence electrons.

Shell is a principal energy level defined by a given value of n, where n can be 1,2,3,4 etc… and is capable of holding 2n2 electrons.

An orbital is a region of three-dimensional space around an atom within which there is a significant probability (usually shown as 90%) that a given electron will be found.

Subshells have different energy levels (orbitals) within a given shell

Slide 40

Valence Electrons

The valence electrons

•determine the chemical properties of the elements.

•are the electrons in the highest energy level.

•are related to the group number of the element.

Example: Phosphorus has 5 valence electrons.

5 valence electrons

P Group 5A(15) 2, 8, 5

Slide 41

Groups and Valence Electrons

All the elements in a group have the same number of

valence electrons.

Example: Elements in group 2A(2) have two (2) valence electrons.

Be 2, 2

Mg 2, 8, 2

Ca 2, 8, 8, 2

Sr 2, 8, 18, 8, 2

Slide 42

Periodic Table and Valence Electrons

Representative Elements Group Numbers

1 2 3 4 5 6 7 8

H He

1 2

Li Be Al C N O F Ne

2,1 2,2 2,3 2,4 2,5 2,6 2,7 2,8

Li Mg Ge Si P S Cl Ar

2,8,1 2,8,2 2,8,3 2,8,4 2,8,5 2,8,6 2,8,7 2,8,8

Slide 43

Learning Check

State the number of valence electrons for each.

A. O

1) 4 2) 6 3) 8

B. Al

1) 13 2) 3 3) 1

C. Cl

1) 2 2) 5 3) 7

Slide 44

Solution

State the number of valence electrons for each.

A. O

2) 6

B. Al

2) 3

C. Cl

3) 7

Slide 45