Chapter 6 - Electronegativity and Intermolecular Forces Flashcards
Define electronegativity
The attraction of a bonded atom for the pair of electrons in a covalent bond
Fill out the electronegativity differences
Covalent = _____
Polar covalent = _____
Ionic = _____
Covalent = 0
Polar covalent = 0-1.8
Ionic = higher than 1.8
Define polar covalent bond
Where the electron pair is not shared equally between the two bonded atoms
A bond will be nonpolar when…
- the bonded atoms are the same
- the bonded atoms have the same or similar electronegativity
Define dipole in simple terms
Separation of opposite charges in a molecule where one region has a small positive charge and the other has a small negative charge
What are the three types of dipoles?
1) permanent dipoles
2) instantaneous dipoles
3) induced dipoles
Define permanent dipole
The dipole in a polar covalent bond
What determines whether a molecule is polar or not? (two factors)
- Must contain one or more polar bonds
2. The molecule must be asymmetrical so the dipole isn’t cancelled
What elements can hydrogen from hydrogen bonds with?
Fluorine
oxygen
nitrogen
What do you consider when comparing melting and boiling points of molecules? (3 things)
- intermolecular forces
- molecular mass
- hydrogen bonds?
Name three weak forces of attraction/intermolecular forces, in order of increasing strength
— London dispersion forces
— permanent – permanent dipole interactions
— Hydrogen bonds
Name three strong forces of attraction/ not intermolecular forces
— ionic
— covalent
— metallic
What properties or molecule the intermolecular forces influence/affect?
melting point
boiling point
solubility
vapour pressure
What is the alternative name for London dispersion forces?
Temporary/instantaneous dipole induced dipole interactions
OR Induced dipole dipole interactions
Does Van der waal’s forces include?
London forces and permanent interactions
How do London forces arise? (3 detailed points)
—The random distribution of electrons in an atom/molecule causes one side of the molecule to become slightly more negatively charged and the other side. This is called an instantaneous dipole.
—The slightly more negative region of this particle repose electrons in a neighbouring particle creating an induced dipole/it polarises it
— This creates an attractive force between the negative and positive poles of the molecules
What is and how does an instantaneous dipole arise?
When at a point in time the random shifting of electrons causes one side of a molecule to become more negatively charged than the other.
What is an induced dipole and how does it arise?
The slightly more negative region in an instantaneous dipole repels electrons in the neighbouring molecule, polarising it and thus induces (creates) a dipole.
What happens to the intermolecular forces and covalent bonds with a simple molecular lattice is broken apart during melting?
Intermolecular forces break
Covalent bonds don’t break
Nonpolar simple molecular compounds tend to be what in polar solvents and why?
Insoluble because there is little interaction between the molecules in the lattice and the solvent molecules thus the molecule doesn’t dissolve
Why do you simple molecular structures not conduct electricity?
No mobile charged particles so nothing to complete electric circuit
Name a few anomalous properties of water
— Solid water/ice is less dense than liquid water
— Relatively high melting/boiling point
— High surface tension
— Low viscosity
Why does water have a high melting and boiling point?
It has (as with all molecules) London forces BUT also has hydrogen bonds
Why is solid ice (below 4°C) less dense than liquid water?
The orientation of hydrogen bonds means there is a limit to how close to molecules can get
What do polar molecules have both of?
Induced dipole interactions AND permanent dipole dipole interactions
Higher Mr/electron number effect in London forces?
Stronger London forces
Polar compounds dissolved in ___ solvents.
Nonpolar compounds dissolved in ____ solvents.
Polar
nonpolar
