Bonding And Structure Flashcards
What does a polar covalent bond look like?
There is a difference in electronegativity so bonding electrons are shared unequally between 2 atoms and there are partial charges on atoms
What should occur for a molecule to be considered polar?
-must contain polar bonds
-dipoles on the bonds shouldn’t be cancelled out through symmetry(molecule must be non symmetrical)
What is ionic bonding?
The electrostatic attraction between oppositelt charger ions
What are solid ionic compounds arranged in
A giant lattice
What is an ionic lattice
A structure with a repeating pattern of oppositely charged ions
What are some key points for dot and cross diagram
-Ions have square brackets around them
-charges must be shown
Define covalent bonding
Electrostatic attraction between a shared pair of electrons and the nuclei of bonded atoms
What is the 8 electron rule?
-The elements C,N,O and F always end up with 8 electrons in their outer shell. This is the most stable arrangement for them
-many elements can have more than 8 electrons in their outer shell
What is a dative(co ordinate bond) covalent bond?
A covalent bond where both of the shared electrons come from the same atom
What does each added lone pair reduce the bond angle by?
2.5°
What does electronegativity refer to?
-the ability of an atom to attract a bonding pair of electrons in a covalent bond
What is the general trend in periodic table for electronegativity?
-elements get more electronegtauve from left to right and from bottom to top
-fluorine is the most electronegative
What are some factors that affect electrostatic attraction?
-charge on the nucleus
-shielding
-distance between the nucleus and the electrons in the bond
Describe the charge on the nucleus trend in periodic table
-As we go from left to right across a period, the charge on the nucleus increases(more protons are added to the nucleus)
-hence the attraction between the nucleus and the bonding electrons increases
-hence the electronegativity increases
-charge on nucleus increases aa you go down group but electronegativity does not increase due to shielding
Describe the trend in shielding in periodic table
-increases down the group
-reduces attraction between the nucleus and bonding electrons
Describe the distance between nucleus and bonding electrons
-across a period(left to right) distance between nucleus and bonding electrons descreases(increasing nuclear charge same shielding so increased attraction between them)
-down a group(top to bottom) distance between nucleus and bonding electrons increases(more shells)
What us a non polar covalent bond
-same electronegativity
-bonding electrons are shared equally between 2 atoms
-no charges on atoms
What are the 3 intermolecular forces
-London forces(Van der Waals forces)
-Permanent dipole-dipole interactions
-hydrogen bonds
how are london forces created
-movement of electrons produces a changing dipole in a molecule.
-an instantaneous dipole will exist but its position is constantly shifting
-the instantaneous dipole induces a dipole on a neighbouring molecule
-the induced dipole induces further dipoles on neighbouring molecules which then attract one another
How do London forces get stronger?
-the more electrons there are, the stronger the London force get
why do the london forces get stronger as there are more electrons?
-can create a larger transient dipole which creates larger transient dipoles on other molecules
-larger dipoles mean a stronger force of attraction between molecules
How can a substance be evaporated?
-intermolecular forces must be broken
-the stronger the intermolecular forces, the more energy required to break them
-so the higher the boiling point
What forces do all molecular substances have?
-London forces of attraction
-usually very weak and don’t require much energy to overcome
-other types of IMF are usually stronger
Permanent dipole-dipole forces
-if molecules posses an overall permanent dipole, these dipoles can interact
Which forces are stronger, London forces or permanent dipole dipole forces?
Permanent dipole dipole forces tend to be much stronger
when does hydrogen bonding occur?
-occurs between a hydrogen atom which is bonded to O, N or F and the lone pair of electrons on the very electronegative atom(o,N of F)
What unique properties does hydrogen bonding give to water?
-surface tension
-excellent solvent
-liquid at room temperature
Hydrogen bonding-ice
-each water molecule is bonded to 4 others in a tetrahedral formation
-volume is largee than the liquid
-when ice melts the structure collapses slightly and the molecules come closer which is why ice floats
Why do ionic compounds have high melting points?
-strong ionic bonds which require a lot of energy to overcome
Why can ionic compounds dissolve in water?
-water is polar therefore can form electrostatic forces of attraction to the dissolved ions
define a lattice
-regular repeating pattern of particles
what is a simple molecular lattice?
-regular repeating pattern of molecules
What forces must be broken to melt(or evaporate) a simple molecular lattice
-London forces
Why do simple molecular substances have low melting points?
-lattice is held together by relatively weak intermolecular forces, which don’t require much energy to overcome
What molecules will polar solvents dissolve
-polar molecules
what molecules will non polar solvents dissolve
-non polar molecules
why do non polar solvents only dissolve non polar molecules?
-they only have london forces acting between them so they can form the same weak interactions with a non polar solvent
Why don’t polar solvents dissolve non polar molecules?
-polar solvents have stronger permanent dipole dipole interactions between the molecules so mixing non polar molecules in with this will disrupt these forces, so non polar substances do not dissolve in polar solvents
Why don’t simple molecular substances conduct electricity as a solid, liquid or solution
-they do not contain mobile electrons or ions so they cannot conduct electricity
