Chapter 6 Flashcards
What is the VSEPR theory?
VSEPR theory says that all electrons are negative so electron pairs repel and the amount repulsion determines the angles of the bonds and that’s the shape of the molecule
Do bonding pairs or lone pairs have the largest repulsion?
Lone pairs have the largest repulsion
When drawing molecules what do a straight line a shaded wedge a non shaded wedge
A struggle line means a bond in the plane
A shaded wedge means a bond coming out of the plane
A non shaded wedge means a blonde going into the plane
What is the Shape and angles of a molecule with two bonded electron pairs?
It has a linear shape and 180° angles
What is the shape and angles of a molecule with three bonded electron pairs?
It has a Trigano planar shapeAnd 120° angles
What is the shapes and angles of a molecule with for bonded pairs of electrons?
It has a tetrahedral shape and 109.5° angles
What is the shape and angles of a molecule with three bonded pairs of electrons and one lone pair of electrons?
It has a triagonal pyramidal shape and 107° bonds
What is the shape and angles of a molecule with two bonded and two lone pairs of electrons?
It has a non-linear shape and 104.5° angles
What is the shape and angles of a molecule with five bonded pairs of electrons?
It has a triagonal bipyramidal shape and also 90 and 120° bonds
What is the shape and angles in a molecule with six bonded pairs of electrons?
Has octahedral shape and 90° bonds
Definition of electronegativity
Electronegativity is the ability of an atom to attract the bonding electrons in a covalent bond
What is electronegativity based on?
Electronegativity is based on nuclear charge, atomic radius and shielding
In what direction does electronegativity increase in the periodic table?
Electronegativity increases towards fluorine in the periodic table
What is Pauling scale?
Paulings scale displays all electronegativity values
What is a polar bond?
A polar bond is a bond that occurs when there is a difference in electronegativity between the atoms in a covalent bond to the bonding electrons are pulled towards a more electronegative atom making it slightly more negative causing a permanent dipole
What is a dipole?
A dipole is a difference in charge due to a shift in the electron density
So what is a polar molecule?
Polar molecule is a molecule where the charge is arranged unevenly so the molecule have an overall dipole
Is a molecule that has polar bonds always a polar molecule?What cases would it not be
If the polar bonds are symmetrical the dipoles cancel each other out there is no overall dipole and the molecule is nonpolar
Name the first type of intermolecular force
London forces – are induced dipole dipole interactions between all atoms and molecules caused by the constant random movement of electrons towards or away from the nuclei which create temporary dipoles
When are London forces stronger?
London forced are stronger when the atom has more electrons
Name the second type of intermolecular force
Permanent dipole dipole interactions- The Delta plus and Delta minus charges and polar molecules cause week electrostatic forces between molecules
Name the third type of Intermolecular forces
Hydrogen bonding – only occurs when hydrogen is covalently bonded to fluorine, nitrogen oxygen because hydrogen is so small and they are so electronegative the bond is so polarised a weak bond forms
Why is solid ice less dense than water?
Water molecules have 2 bonded and 2 line pairs allowing it to form four hydrogen bonds Which hold water molecules apart in an open lattice structure. They are held further apart in ice than water as when it melts the lattice collapses so ice is less dense.
Why does water have relatively high melting and boiling points?
Hydrogen bonds needs a lot of energy to overcome the electrostatic forces of attraction
What is a simple molecular lattice?
A simple molecular lattice is made up of simple molecules (iodine, ice) the molecules are held in place by weak intermolecular forces and the atoms within each molecule are held by covelant bonds.
What are the properties of simple molecular substances and why
- Low Melting and boiling points as the week into molecular forces can be broken by low energy
- solubility- soluble Iin non polar solvents as forces form between the molecule and the solvent weakening those in the lattice
Insoluble in polar solvents as the bonding in polar solvents is too strong to be broken - non conductors - no mobile charged particles
What is a simple molecule ?
small units containing a definite number of atoms with a definite formula
