Lesson 2 Matter
Organization of the Periodic Table
Did you know that Dmitri Mendeleev is often referred to as the Father of the Periodic Table?
B2.43 Dimitri Mendeleev
Dimitri Mendeleev, a Russian chemist, recognized that all of the known elements at the time created a pattern. It was such a distinct pattern that Mendeleev actually predicted the discovery of elements that would fit into the missing places.
Over time, those elements were discovered and they did have the properties that Mendeleev predicted they would have.
The term periodic means at regular intervals; so the elements are arranged in such a way on the periodic table that elements that have similar atomic structure and characteristics create repetitive patterns.
The term periodic means at regular intervals; so the elements are arranged in such a way on the periodic table that elements that have similar atomic structure and characteristics create repetitive patterns.
Did You Know?
Which element displays the most metallic character? Did you think of copper or iron? These are common metals, but they do not actually contain the most metallic character of all the elements. Watch this video to learn which element is considered
the “most metallic” and which element is considered the “most non-metallic.”Learn More
B2.44 Periodic table
The modern periodic table is organized in increasing atomic numbers.
- Horizontal rows are known as periods and relate to the number of energy levels in an atom.
- Vertical columns are known as groups or families and relate to the number of valence electrons, which are the electrons located in the outer most energy level, or valence energy level.
- For groups 1, 2, and 13 to 18, the last digit of the group number is the same as the number of valence electrons for that element. (Valence electrons will become very important when we discuss compound formation in the next section.)
For example, if we study the modified Bohr diagrams for lithium, potassium, aluminium, and argon and relate their structures to their placement on the periodic table, we will see clear trends emerge.
| Element | lithium | potassium | aluminum | argon |
|---|---|---|---|---|
| Modified Bohr Diagram |
 |
 |
 |
 |
| Group Number |
1 | 1 | 13 | 18 |
|
Number of Valence Electrons |
1 | 1 | 3 | 8 |
| Period Number |
2 | 4 | 3 | 3 |
|
Number of Energy Levels |
2 | 4 | 3 | 3 |
These patterns can be used to predict the atomic structure of elements without needing to model it with a modified Bohr diagram. These patterns are also important to note when we start to investigate chemical reactivity, such as group 1 alkali metals being very chemically reactive while group 2 alkaline-earth metals are less reactive. Group 18 noble gases are stable, whereas group 17 halogens are very reactive, especially with alkali metals. These concepts will be addressed later on in this unit; but do you have a theory based on what you have learned so far?
The staircase line separates metals on the left from non-metals on the right, with the exception of hydrogen, as it is a non-metal.
These categories are in place based on shared characteristics between the elements that are classified as metals and those that are classified as non-metals. Further categorization is given to eight elements that border the staircase line. These elements, identified as metalloids, have some metallic properties and some non-metallic properties.
| Metals | Non-metals | Metalloids |
|---|---|---|
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Watch This
Alkali Metals in Water – Chemical Elements: Properties and Reactions @ YouTube OpenLearn from the Open University
This video will illustrate how elements of one group have similar properties.