Chemical Symbols in the Periodic Table

How is the Periodic Table Arranged?

1. Alphabetically from A to Z

2. By atomic mass, from small to large

3. By number of protons, starting with 1

4. Randomly

5. In the order the elements were discovered

Periodic table is arranged by number of protons!

This is also by Atomic Number

By coincidence, the elements are generally in order of increasing atomic mass, but not always…..

For example….

Cobalt has 27 protons, mass = 58.9 amu

Next after Co comes Nickel

Nickel has 28 protons , but mass = 58.7 amu (less mass than cobalt)

Periods

Periods are the horizontal rows. There are 7 periods

1

23

4

5

6

7

(6)(7)

Groups or Families

Groups (also called families) are the vertical columns. There are 18 groups.

1 18

Most elements are metals

Non-metals live in upper right corner (except Hydrogen)

6 Metalloids live near the red stair:B, Si, Ge, As, Sb, Te

X

Group 1 metals are called alkali metals

Group 2 metals are called alkaline earth metals

Transition Metals are in groups 3 through 12They tend to form colorful ions and

compounds

Halogens are in group 17 Noble gases in group 18

7 elements are DIATOMIC

Allotropes

Elements that can exist in different forms in the same phase are allotropes:

O2 (oxygen gas) and O3 (ozone) are allotropes

Allotropes have different chemical and physical properties

Valence Electrons

Definition: all the electrons in an atom’s

HIGHEST ENERGY LEVEL

Valence Electrons

Remember: There are seven energy levels

Energy Level 1 can hold two e- in S orbital

Energy Level 2 can hold two e- in S, 6 in P

Energy Level 3 : S, P, D

Energy Level 4-7: S, P, D, F

However….

Since according to the aufbau principle d and f orbitals fill after the S and P orbitals in the next highest energy level,

Valence electrons are always in S or P orbitals

(2 in S) + (6 in P) = 8 (max) Valence e-

How to determine which e- are valence e- :

Step 1: Write out the electron configuration for the atom

11Na = 1S2 2S2 2P6 3S1

Step 2: Count how many e- in the highest energy level:

Energy level 3 = highest, so there is 1 valence e-

Level 3 is highest

The good news:

It is easy to determine valence e- simply by looking at the periodic table:

Group 1 has 1 valence e-Group 2 has 2 Group 13 has 3Group 14 has 4Group 15 has 5…….. Group 18 has 8

What about the transition metals?

For now, assume that they have 2.

But sometimes they can also have 1, or 3 or more

Write out the e- configuration for the following elements, then check and see what Group they are in:

12Mg

8O

17Cl

18Kr

26Fe

19K