Transcript Using the Periodic Table - Red Hook Central Schools

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
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
2 2S2 2P6 3S1
Na
=
1S
11
Level 3 is highest
Step 2: Count how many e- in the highest energy
level:
Energy level 3 = highest, so there is 1 valence e-
The good news:
It is easy to determine valence e- simply by
looking at the periodic table:
Group 1 has 1 valence eGroup 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