VESPR theory Flashcards
What does VESPR theory stand for?
Valence shell electron pair repulsion theory
What does VESPR help scientists do?
predict a 3d shape of a molecule centered around a central atom
Why do molecules form geometric shapes?
Electrons don’t want to be next to each other because like repels like and the negative charges repel each other. Since there are several electron, the electrons have to find positions where they are as far away from each other as possible
What are the two main rules in VESPR theory?
Electron pairs in the valence shell of an atom will repel or move away from each other
nonbonded electron pairs are found closer to the atom and exhibit more repulsion than nonbonded pairs
What are the 5 basic shapes of VESPR molecules?
in this def, a “line” can be a single, double, or triple bond
-linear (1 or 2 “lines”, just a straight line)
-trigonal planar (one atom in the middle and 3 “lines, looks like half of a pyramid)
-tetrahedral (one atom in the middle and 4 “lines”, looks like a pyramid. all faces of the shape created are triangles)
-trigonal bipyramidal (2 pyramids that share a base, 1 central atom and 5 “lines”)
octahedral (vertices make up an octahedron when connected, 1 central atom and 6 “lines”)
How can you figure out the angles within the VESPR structures?
Since electrons want to get as far away from each other as possible, their angles are 360/the number of “lines”
(in our def, a “line” is any kind of bond - single, double, etc)
Covalent bonds can be ____ or ______
polar or nonpolar
Why is polarity important?
It determines other physical properties of the compound, like boiling point, melting point, solubility, and intermolecular interactions
What are nonpolar bonds?
Bonds where the atoms share electrons equally because of similar electronegativities
(in other words, compounds with elements with similar electronegativities will be nonpolar)
What are polar bonds?
Bonds where the atoms share the electrons unequally because the atom have different electronegativities
All ionic bonds are ____
polar
What is a dipole?
The small difference in charge that occurs when one atom is closer to the bonded electron pair
What does δ+ mean (in reference to dipoles)
slightly positive
What does δ- mean (in reference to dipoles)
slightly negative
What is a dipole moment? How is it shown?
the occurrence of a dipole
an arrow that shows which direction the electrons are moving to (the element accepting the electron). There is also a small vertical line that shows which element is donating the electron)
(look up “dipole moment” for references)
Nonpolar covalent bonds form between atoms with an electronegativity difference between _ and ___
0
- 4
(ex: carbon and hydrogen have respective electronegativities of 2.5 and 2.1, which have a difference of 0.4. their compound is nonpolar)
Polar covalent bonds form between atoms with an electronegativity difference between __ and __
- 5
1. 7
Bonds are polar if ______. The entire molecule is polar if _____
the atoms have an electronegativity difference greater than 0.5
the shape is asymmetric (SNAP: Symmetrical molecules are Nonpolar and Asymmetric molecules are Polar)
Can a molecule be nonpolar but the bonds are polar at the same time?
Yes
What does it mean if bonding atoms are delocalized?
They are free to move around
How do metallic bonds form?
Bonding atoms are delocalized and form a negative electron sea around positive cations.
What are some properties of metals with metallic bonds?
- good conductor of electricity and heat
- high melting point and high boiling point
- high density
- malleable and ductile
What does the strength of a metallic bond depend on?
The number of electrons free to move around the metal and the size and charge of the cation.
What is an intramolecular force?
A force that holds the molecule together
What is an intermolecular force?
The forces between molecules that influence their physical properties
List the intermolecular forces from weakest to strongest
London dispersion force
Dipole-Dipole interactions
Hydrogen bonding
What are London dispersion forces?
weak attractive forces that are created by the movement of electron which attracts the positive nucleus of another atom
-leads to a temporary dipole that loosely keeps atoms together
How do london dispersion forces get stronger?
With more electrons
What are dipole forces?
Attraction forces between two polar molecules (opposite charges attract, positive end of polar molecule attracts negative end of other polar molecule)
The larger the dipole moment, the larger the _____ in dipole dipole interactions
attractive force
What is a dipole moment?
Measurement of the size of a dipole
Are hydrogen bonds actual bonds?
NO
much weaker than covalent, metallic, or ionic bonding
Hydrogen bonds are the intermolecular forces between which elements?
Hydrogen, Fluorine, Oxygen, and Nitrogen
How do intermolecular force relate to the different states of matter?
Solids have strong intermolecular forces
liquids have medium strength intermolecular forces
gases have weak intermolecular forces
What does having weaker intermolecular forces mean?
Lower boiling points and melting points
What does having stronger intermolecular forces mean?
Higher boiling points and melting points
What intermolecular forces can Noble gases have?
Only London dispersion forces
