Basics
• Topic One •
Valence Electrons
These are the electrons in the outermost electron shell of an atom, and are farthest away from the nucleus.
Atomic Radius
This is a measure of the size of an atom. It is influenced most by the number of energy levels in an atom, but also by its nuclear charge.
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It is measured from the nucleus to the outermost electron shell.
Electronegativity
This is the relative attraction of a bonded atom to electrons in the bond. This influences whether a bond is ionic, covalent, or polar covalent. It is influenced by the shielding effect (amount of inner-shell electrons) and the nuclear charge.
Trends
As you go up and across the periodic table, starting in the bottom left corner, atomic radius decreases, and electronegativity increases.
Ionic Bonds
One atom steals an electron and become an anion. The other loses an electron and becomes a cation. These bonds form due to a large difference in electronegativity.
Lewis Dot Structures
These are used to denote the structure of compounds. Bonds are a line that represent two electrons that are shared by both atoms that it is connected to. Each dot represents a singular electron.
Resonance Structures
These are used to show the multiple ways that compounds can be structured.
Polar vs Nonpolar Bonds
In nonpolar bonds the electrons are shared equally because there is very little difference in electronegativity between the atoms. In polar bonds the electrons are shared unequally due to a difference in electronegativity. The electron cloud is shifted towards the more electronegative atom.
Polar vs Nonpolar Molecules
Nonpolar molecules either have all nonpolar bonds, or are symmetrical, or both. Polar molecules have one side that a little positive and one side that's a little negative. Polar molecules must have polar bonds and be asymmetrical.