Module 3 - Bonding and Structure Flashcards
Why do atoms bond?
To lower their potential; allows unpaired electrons to become paired
What is the octet rule?
Main group elements bond in such a way that each atom has eight electrons (a completed valence)
What are the 3 types of chemical bonds?
- Ionic
- Covalent
- Metallic
What 2 chemical properties are ionic bonds based on?
Ionization energies and electron affinity
What is ionization energy?
Ability to give up an electron - function of atomic radius
What is electron affinity?
Ability to accept an electron
What are the 2 types of covalent bonds based on differences in electronegativity?
Polar - electrons not shared equally
Nonpolar - electrons shared equally (C-H or 2 of the same element)
How many electrons are in single, double, and triple bonds?
- 1 line = single bond (2 electrons)
- 2 lines = double bond (4 electrons)
- 3 lines = triple bond (6 electrons)
What are the 4 steps to drawing Lewis Structures for atoms?
- Determine the number of valence electrons
- Draw the chemical symbol
- Place one dot on each side of the chemical symbol
- Any remaining electrons are paired until no electrons remain
What are the exceptions to the octet rule?
- Hydrogen (two electrons)
- Boron (six electrons)
- Aluminum (six electrons)
- Expanded octets
How are expanded octets an exception to the octet rule?
- Ten or twelve electrons are possible
- Only occurs in period three elements or higher
- All thanks to d-orbitals (close enough in energy to the outer shell and can, therefore accept some electrons)
What are the 4 steps to drawing Lewis Structures for compounds?
- Count the total number of electrons available
- Draw skeletal structure (central atom + peripheral atoms + bonds)
- Fill octets of peripheral atoms by adding lone pair electrons
- Add any remaining electrons to the central atom as lone pair electrons
- Calculate any formal charges (FC)
What direction do you add electrons in dots for lewis structures?
Clockwise
How do you know which atom is the central atom?
Atom with lowest electronegativity
- also multiple of an atom in a chemical formula probably won’t be the central atom
The best structure will ________ formal charges
Minimize
How is formal charge calculated?
FC = VE -LPE -1/2BE
- Valence Electrons (VE)
- Lone Pair Electrons (LPE)
- Bonding Electrons (BE)
Theory based on the idea that electron groups (lone pairs, single bonds, multiple bonds, single electrons) repel one another; achieve maximum separation
Valence Shell Electron Pair Repulsion (VSEPR) Theory
For molecules having one central atom, geometry depends on:
- # of electron groups around central atom
- how many of those electron groups are bonding groups and how many are lone pairs
AXE nomenclature
A = central atom
X = peripheral atom
E = lone pair electrons
VSEPR theory is used to determine
electron and molecular geometry
____________ is the total number of electron groups => big picture
Electronic geometry (AX4)
__________ determines the total + of atoms and lone pairs around central atom
Molecular geometry (AX3E)
Linear (2e groups)
Bonding angle = 180°
- Electron Geometry = AX2
- Molecular Geometry = AX2
Trigonal planar
Bonding Angle = 120°
- Electron Geometry = AX3
- Molecular Geometry = AX3
Bent (3e groups)
Bonding Angle = < 120 °
- Electron Geometry = AX3 (trigonal planar)
- Molecular Geometry = AX2E
Tetrahedral
Bonding Angle = 109.5°
- Electron Geometry = AX4
- Molecular Geometry = AX4
Trigonal Pyramidal
Bonding Angle = < 109.5°
- Electron Geometry = AX4 (tetrahedral)
- Molecular Geometry = AX3E
Bent (4e groups)
Bonding Angle = < 109.5°
- Electron Geometry = AX4 (tetrahedral)
- Molecular Geometry = AX2E2
Trigonal Bipyramidal
Bonding Angle = 180°, 120°, 90°
- Electron Geometry = AX5
- Molecular Geometry = AX5
See-Saw
Bonding Angle = 180°, 90°
- Electron Geometry = AX5 (Trigonal Bipyramidal)
- Molecular Geometry = AX4E
T-Shaped
Bonding Angle = 180°, 90°
- Electron Geometry = AX5 (Trigonal Bipyramidal)
- Molecular Geometry = AX3E2
Linear (5e groups)
Bonding Angle = 180°
- Electron Geometry = AX5 (Trigonal Bipyramidal)
- Molecular Geometry = AX2E3
Octahedral
Bonding Angle = 180°, 90°
- Electron Geometry = AX6
- Molecular Geometry = AX6
Square Pyramidal
Bonding Angle = 180°, 90°
- Electron Geometry = AX6 (Octahedral)
- Molecular Geometry = AX5E
Square Planar
Bonding Angle = 180°, 90°
- Electron Geometry = AX6 (Octahedral)
- Molecular Geometry = AX4E2
What are the steps to predicting molecular geometries?
- Draw the Lewis Structure
- Determine the total number of electron groups (electron geometry)
- Determine the total number of atoms and lone pairs around central atom (molecular geometry)
How many electron groups make a compound 3D?
4 and more; chirality
