3 - Elements of the Second Row
Core Colors of Main Block Elements
Since the ChemStudy program that revolutionized chemistry teaching in the sixties, these elements have been emphasized to define the properties of the main block elements. The Ross model helps learners understand how these elements "work."
1. Core Charge Matches Group Number
The first thing to notice is that the core charge increases monotonically across the row. Notice that the group number of the column on the periodic table matches the core charge (or the core charge plus 10). This feature is also true for the main block elements of rows 3, 4, 5, and 6.
The core charge influences all of the chemical behavior of the Row 2 elements.
2. Valence Electrons = Core Charge
Of course! In a neutral atom, the number of valence electrons must equal the core charge.
Now the student's difficulties are reduced to just two things:
- the core charge is a list of integers from one to eight
- whatever the core charge is, that's the number of valence electrons
This is much simpler than the Bohr-Rutherford model
3. Atomic Radius Decreases Left to Right
Let the student choose any radius for Li, the lithium atom. Will the radius of the Be atom be larger or smaller than Li?
The student can easily explain why the radius decreases: the stronger the core charge, the stronger the pull on the valence electrons.
Furthermore, the closer the valence electrons are to the core, the stronger the pull. Students can intuitively use core charge and radius to judge the strength of the attraction that the electrons experience.
4. Core Color Related to Electronegativity
Remember the ambiguous exercise 6 in Lesson 2? Carbon was compared with phosphorus. Students could not reliably decide which atom got the free electron. To resolve this issue, we must use the concept of electronegativity.
There are many electronegativity scales. The Ross model is a blend of electronegativity scales, so that the electronegativity scale increases by 0.5 at for each consecutive element. The electronegativity number can be found above and to the right of each element's chemical symbol.
One more detail: the electronegativity scale is mapped onto the color scale:
The color of each atom's core represents the that element's electronegativity.
5. The Ross Model is a Pedagogical Model
There are only three salient features: core charge, valence occupation, and radius.
Students can intuitively judge whether any valence electron is strongly or weakly attracted to the atom by examining just two things:
- The stronger the core charge, the greater the electronegativity.
- The smaller the radius, the stronger the electronegativity.
Using these two judgments, students can predict and explain a huge number of chemical phenomena! This periodic table is designed so that students can learn chemistry intuitively.
Many teachers have asked "Can we really just change the Bohr-Rutherford model of the atom? Is that allowed? Isn't that against science?"
Find out why we left the Bohr-Rutherford model behind - Lesson 4.
Lesson 1 - Learn the three salient features of each atom, and follow how they change across the periodic table.
Lesson 2 - Learn how students can make accurate predictions, with nearly no instruction!
Lesson 3 - Take a closer look at the elements of the second row.
Lesson 4 - Origins of the Ross model of the atom
Lesson 5 - Covalent bonding
Lesson 6 - Ionic Bonding
Lesson 7 - A post-modern model of science.
Lesson 8 - Learning with IntuitivScience.