4.3 Covalent Structures Flashcards
Octect Rule
states that the most stable arrangement for an atom is to have eight electrons in its outermost energy level with the electron configuration of a noble gas.
Exceptions to the Octect Rule
Hydrogen is stable with only two electrons in its outer shell.
Atoms such as boron, beryllium and aluminium (in compounds) are stable with fewer than eight electrons in their outer shell.
Atoms in period three and higher, such as sulfur, can form expanded octets with up to twelve electrons in their valence shell.
Incomplete Octect
Definition
Molecules that are electron-deficient do not have a full outer shell of electrons.
they are stable with less than eight electrons in their valence shells.
Example: BF3 and BeCl2
Expanded octets
Elements in period 3 and beyond can have expanded octets and accommodate more than eight electrons in their valence shells.
Lewis Structure
Lewis structures (also known as electron dot diagrams) represent the bonding in a molecule; they show both the bonding electrons and the non-bonding electrons (or lone pairs).
net dipole moment
The net (or overall) dipole moment of a molecule is a measure of its overall polarity. It is the sum of all the bond dipoles in a molecule.
Name 3 molecules and ions that have resonance structures
C6H6
ozone
O3
polyatomic ions that contain multiple bonds (such as the carbonate ion, CO32-).
Resonance Structurre
When molecules contain multiple bonds (double or triple bonds), there is more than one possible Lewis structure that can be drawn.
VESPR theory
According to this theory, electron pairs in molecules repel each other and orientate themselves as far away from each other as possible .A molecule will adopt the shape that minimises the repulsion between the electron pairs.
Electron Domains
Both bonding electrons and non-bonding electrons are collectively known as electron domains.
Molecules with _ electron domains around the central atom have both a _ molecular geometry and electron domain geometry.
Molecules with two electron domains around the central atom have both a linear molecular geometry and electron domain geometry.
Molecules (or polyatomic ions) with _ electron domains around the central atom have a trigonal planar (or triangular planar) electron domain geometry.
Molecules (or polyatomic ions) with three electron domains around the central atom have a trigonal planar (or triangular planar) electron domain geometry.
When would a molecule be v-shaped?
The molecular geometry can be either trigonal planar or bent (or V-shaped), depending on the presence of lone pairs of electrons on the central atom (Figure 3). If there are no lone pairs of electrons present, the molecular geometry will be trigonal planar; if a lone pair of electrons is present, it will be bent.
bent geometry is caused by what?
The bent geometry is caused by the stronger repulsion that exists between the non-bonding electrons and the bonding electrons on the central atom compared to the weaker repulsion that exists between the bonding electrons.
