Chemical Symbols in the Periodic Table

How is the Periodic Table Arranged? Alphabetically from A to Z By atomic mass, from small to large By number of protons, starting with 1 Randomly 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 2 3 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 12 They 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 3 Group 14 has 4 Group 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