Study Notes on Electron Configuration, Valence Electrons, and Periodic Trends
Electron Configuration and Valence Electrons
Many elements end in certain orbitals (e.g., two s one, three s two, three s one, four s one).
These elements belong to specific groups in the periodic table. For example:
Group 1A: Elements ending in a single s orbital.
Elements noted with an ending of 5 electrons share that in their configuration ending.
When combining two elements with similar configurations, they can share a number of electrons.
Both configurations examined here ultimately lead to a total of 7 electrons.
These elements are identified as belonging to Group 7A.
Groups in the Periodic Table:
Group 1A - 1 valence electron
Group 2A - 2 valence electrons
Group 3A - 3 valence electrons
Group 4A - 4 valence electrons
Group 5A - 5 valence electrons
Group 6A - 6 valence electrons
Group 7A - 7 valence electrons
Group 8A - 8 valence electrons
Valence Electrons
Elements' chemical properties largely dictated by the number of valence electrons they possess.
Valence Electrons: Electrons in the highest energy level of an atom.
The group number of elements (1A - 8A) directly correlates with their valence electron count.
Example: Group 1A has one valence electron, Group 7A has seven valence electrons.
Electron Dot Symbols (Lewis Dot Symbols)
Used to simplify representation of valence electrons.
Consist of:
Letter symbols representing elements.
Dots representing each valence electron.
Example of Aluminum (Al):
Aluminum has 3 valence electrons (Group 3A)
Represented as:
Al· · · (three separate dots on different sides)
Example of Nitrogen (N):
Nitrogen has 5 valence electrons (Group 5A)
It is represented with 4 single dots in each position, and the fifth dot is paired:
N· · · · (four separate dots and the fifth paired)
Critical Understanding: Recognizing how to draw these symbols and identify valence electrons is essential.
Atomic Structure and Orbital Limits
Orbital Capacities:
s orbitals hold a maximum of 2 electrons.
p orbitals hold a maximum of 6 electrons.
d orbitals hold a maximum of 10 electrons.
Understanding sequence and limits of orbitals is crucial up to 4s.
Trends in the Periodic Table
Focus on main group elements (Groups 1A to 8A) for periodic trends.
Atomic Size
Definition: Size of an atom is defined by the area occupied by electrons.
Atomic size trends:
Top to Bottom: Increases as more subshells are added.
Left to Right: Decreases due to increased positive charge attracting electrons closer to the nucleus.
Example:** Sodium (Na) → Chlorine (Cl): Atom size decreases.
Ionization Energy
Definition: Energy required to remove an electron from the valence shell.
Trends in ionization energy:
Top to Bottom: Decreases; as atomic size increases, valence electrons are further from the nucleus, requiring less energy to remove them.
Example:** Lithium (Li) requires more energy to remove an electron compared to Potassium (K).
Left to Right: Increases; atoms get smaller as protons attract electrons more strongly, requiring more energy to remove them.
Example:** Energy increases across the period from left (Na) to right (Cl).
Energy Levels and Stability
Electrons closest to the nucleus have lower energy, as they maintain a stable interaction with the nucleus.
Electrons further away from the nucleus possess higher energy, making them more likely to be removed:
This correlation highlights stability; electrons closer experience a stronger pull from protons and thus remain bound more effectively than those farther away.
Conclusion
To summarize:
Atomic size increases as you go from top to bottom in the periodic table and decreases from left to right.
Ionization energy decreases from top to bottom and increases from left to right.
Understanding these trends is crucial for predicting and explaining chemical behavior and reactivity in elements.