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Understanding the Periodic Table: Valence Electrons, Atomic Radius, and Ionization Energy, Lecture notes of Chemistry

University of the Pacific (UOP)Chemistry

The concept of valence electrons in the context of the periodic table, and discusses how valence electrons contribute to periodic trends such as atomic radius and ionization energy. It also introduces the concept of electron dot diagrams and provides examples of writing the full electron configuration and lewis structures for an element.

Typology: Lecture notes

2021/2022

Uploaded on 09/27/2022

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Explaining the Periodic Table
Electron configuration can help explain the structure of the periodic table and periodic trends.
For example: Why is the atomic radius of potassium larger than that of sodium?
Why is the first ionization energy higher in beryllium than in lithium?
Valence Electrons
These are the electrons in the outermost shell (now what we call the
outermost principal quantum level) of an atom.
are the most exposed of all electrons
= the electrons gained or lost in a chemical reaction
show a repeating pattern or ‘periodic trend’ in the Periodic Table
- valence electrons increase across a period
- for the main groups the number of valence electrons a particular atom has is
the same as it Group number using the Classical Numbering System
For example:
Sodium in Group IA has 1 valence electron
Aluminum in Group IIIA has 3 valence electrons
Nitrogen in Group VA has 5 valence electrons
- the number of valence electrons stays the same
down the Main Groups
For example:
Be, Mg, Ca belong to Group IIA = have 2 valence e’s
Transition Metals do not follow the pattern and may have more than 1 valence.
Why??
- as electrons begin to fill the d sublevel, some act as shielding electrons while others
act as valence electrons
- generally, the first electrons into a d sublevel behave like valence e’s, while the last
ones act more shielding e’s = hard to predict!!
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Explaining the Periodic Table

Electron configuration can help explain the structure of the periodic table and periodic trends. For example: Why is the atomic radius of potassium larger than that of sodium? Why is the first ionization energy higher in beryllium than in lithium? Valence Electrons These are the electrons in the outermost shell (now what we call the outermost principal quantum level) of an atom.  are the most exposed of all electrons = the electrons gained or lost in a chemical reaction  show a repeating pattern or ‘periodic trend’ in the Periodic Table

  • valence electrons increase across a period
  • for the main groups the number of valence electrons a particular atom has is the same as it Group number using the Classical Numbering System For example: Sodium in Group IA has 1 valence electron Aluminum in Group IIIA has 3 valence electrons Nitrogen in Group VA has 5 valence electrons - the number of valence electrons stays the same down the Main Groups For example: Be, Mg, Ca belong to Group IIA = have 2 valence e’s  Transition Metals do not follow the pattern and may have more than 1 valence. Why??
  • as electrons begin to fill the d sublevel, some act as shielding electrons while others act as valence electrons
  • generally, the first electrons into a d sublevel behave like valence e’s, while the last ones act more shielding e’s = hard to predict!!

Electron Dot Diagram (aka Lewis Structures)  shorthand way of indicating the number of valence electrons Steps:

  1. The chemical symbol is written in the core.
  2. Valence electrons are represented on 4 sides of the symbol by dots (maximum of 8 dots).
  3. Each side of the element must have one dot before pairing of dots can occur. For example: Example Problem For As, write the: (a) the full electron configuration (b) the Lewis Structure Periodic Trends and Patterns  Elements with the same valence electron configuration show similar chemical behaviour and form the basis for the periodic trends.
  4. Metallic Characteristics  shiny, malleable, ductile, conduct electricity and heat  decrease across the period but increase down the group  These characteristics are related to their ability to lose electrons willingly.