U2 - Module 4: Inferring Charge Distribution Flashcards
What are the two periodic trends?
- Ionization Energy
- Larger for gases - Atomic/Radius Size
-Large for metals
When does nuclear attraction increase?
As the shell size gets smaller.
- Electrons have a stronger bond to the nucleus.
What are the properties of chemical compounds influenced by?
How the valence electrons are distributed among different atoms.
What can the charge distribution of a molecule be determined by?
The structure of the molecule.
What is assumed about molecules and their charges?
That molecules have partial positive and negative charges.
What are lone pairs in a molecule considered?
Electron rich regions
What do molecules have?
Individual and overall charges
Electron Rich Area
- Closer to the nucleus
- Contain mainly electrons
- Negative charge
Electron Poor Area
Where less electrons/lone pairs are located
What causes some atoms to have stronger attractive forces?
They tend to have unfilled valence energy levels that are lower energy than the same energy level in other atoms.
What does it mean when an atom has more filled subshells than an electron that has less filled subshells?
The atom with more filled subshells will require more energy to remove the electrons, rather than one that has less filled.
Electronegativity (X)
A measure of the decrease in the energy of a system if bonding atoms are localized in the area of a given atom.
What is the electronegativity trend?
The same as ionization energy
- Higher for gases
What does electronegativity help predict?
The partial charges on bonded atoms
What does it mean when electronegativity is larger in a given area?
There are more electrons between that given bond.
Dipole Moment
The existence of positive (g+) and negative (g-) charges
How is the dipole moment represented?
An arrow that points from the positive region to the negative region
What is a bond considered if a dipole moment is present?
A polar bond
What does polarity of a molecule tell us?
Chemical properties
What details of chemical properties are in relation to polarity?
Interactions with other molecules and light
Vector Sum
Determines the molecules overall polarity
What does it mean when the vector sum is 0?
The molecule is nonpolar
What affect do lone pairs have on a molecules electronegativity?
It increases electron density, which can affect shape and polarity.
What do bond dipole moments act as?
Vectors; molecular geometry
What happens to the electron density in polar molecules?
They have an uneven electron density distribution
What relation does symmetry have with molecular polarity?
If a molecule is symmetric and has the same surrounding atoms, it will be nonpolar
How can molecules that have no electronegativity difference be polar?
The lone pairs causes different electron densities around each of the atoms, which results in polarity.
How is polarity related to tetrahedral shape?
All tetrahedral molecules are nonpolar unless they have different atoms surrounding the central atom.
How is poalrity related to trigonal planar shape?
All trigonal planar molecules are nonpolar unless they have different atoms surrounding the central atom, or have lone pairs affecting the electron density.
What do nonpolar molecules have?
Fully symmetrical charge distributions
How do you draw the molecular dipole moment?
Start from the area of lowest EN, and point the arrow towards the area of highest EN.
Hydrocarbons
Molecular compounds that only have hydrogens and carbons present
Are hydrocarbons polar or non polar, why?
Nonpolar
- EN differences are very small
- Symmetrical
- No regions of high and low electron density
What happens when a functional group is attatched to a hydrocarbon?
The overall molecule becomes polar
What 4 things should you analyze to determine if a molecule has a dipole moment or not?
- Symmetry (draw Lewis Structure)
- Bond Polarity (EN differences)
- Lone pair distributions (electron density regions)
- Overall shape (symmetrical or bent)
What does molecular polarity influence?
Interactions with light
Greenhouse Effect
The earth has gases that absorb IR which help keep the planet warm by absorbing the solar energy.
Energy absorbed is then re-emitted into the earths surface through photons.
Greenhouse Gases
Substances that absorb and emit IR radiation
What is necessary for a molecule to absorb IR radiation?
There should be a change in its net molecular dipole moment when the molecule vibrates
What are the only molecules that are not IR active?
Diatomic Molecules (same element)
- Cannot be unevenly stretched/bent
Electronegativity
A measure of the ability of an atom in a bond to attract electrons to itself
What do differences in electronegativities between atoms create?
Bond polarity due to an unequal distribution of charge
