3.3 Bonding Flashcards
Describe the properties of an ionic lattice?
Brittle - when layers slide like charged ions are next to each other so repel
High melting and boiling points
Crystalline structure
Conducts when aqueous/molten
Dissolve in polar substances
Describe dative covalent bonding
when one of the atoms donates both of the electrons needed for a covalent bond
one atom donates a pair of electrons
the other atom must have an empty orbital
What is electro negativity?
This is the power of an atom to attract the electron density in a covalent bond towards itself
what effects electronegativity?
The nuclear charge of the atom
the distance between the nucleus and the outer shell electrons as this affects there attraction
the amount of shells that shield the nucleus
definition of metallic bonding
Positive metal ions form electrostatic attraction to delocalised electrons to form a lattice
what affects metallic bond strength ?
The charge of the metal ion - the higher charge means more delocalised electrons present
the size of the ion- the smaller the metal the closer it can get to the nucleus
ergo they will have greater charge density
why do lone ion pairs have the most increasing repulsion?
due to lone ion pairs being a pair of electrons which are very negative, like charges with high density will have the most repulsions
What are van der waal forces?
The random movement of electrons in an atom causes an instaneous dipole which then causes an induced dipole in the next atom. Leading to forces being acted upon them called Vdw.
what effects the strength of dipoles?
the size of the molecule
size of electron cloud
amount of distortion in the electron cloud.
Explain why iodide has a higher boiling point than chlorine?
Iodine has more electrons and is a larger molecule than chlorine
so the electrons will have less attraction to the nucleus making the electron cloud easier to distort.
Allows for stronger temporary dipoles to increase Vdw so more energy required to separate molecules.
How is bond polarity formed?
The electron distribution in a covalent bond between elements with different electronegativities will be unsymmetrical. This produces a polar covalent bond, and may cause a molecule to have a permanent dipole.
how is Hydrogen bonds formed?
The strongest intermolecular force
must contain H-F, N-H, or O-H bonds.
How do you know if molecules are polar or not?
Look at the delta negative and positive charges and the way the polar bonds are facing, if they face into each other then the polarity cancels out.
What is permanent dipole dipole interaction?
Occurs between polar molecules
as the attraction between the delta negative and delta positive of the molecule
this causes an induced dipole on the neighbouring molecule (this is a van der waal force)
Describe a polar bond
Is a bond between atoms of different electronegativities
meaning there is a permanent dipole across molecules
The higher the difference in electronegativity the stronger the bond
describe a non- polar bond
This is between atoms that have the same or similar electronegativities
So there is no permanent dipole so it is just a covalent bond
e.g Carbon and hydrogen have very similar electronegativities so create a simple covalent molecule together.
Explain why pentan-2-ol has a higher boiling point then pent-1-ene
pent-2-ol has stronger intermolecular forces
pent-1-ene has van der waals only
pent-2-ol also has hydrogen bonds.
The melting point of XeF4 is higher than the melting point of PF3
Explain why the melting points of these two compounds are different
XeF4 is a square planar shape
It has 2 lone pairs which repel more then bonding pairs
PF3 is a tetrahedral shape
XeF4 has van der Waal forces and PF3 has van der waals and hydrogen bonds
why is a fluoride ion larger than a sodium ion
Fluoride ion has (two) fewer protons/lower nuclear charge
Weaker attraction between nucleus and (outer) electron
why does ethanol have a boiling point of 78
and methoxymethane have one of -24
Hydrogen bonds (between ethanol molecules
Hydrogen bonds are stronger/est intermolecular force
Explain how the lone pairs of electrons on the oxygen atom influence the bond angle in oxygen difluoride
Lone pairs repel more than bond pairs
bond angle will be lower (than regular tetrahedral angle) / bond angle of
103-106°
There are two lone pairs of electrons on the oxygen atom in a molecule of oxygen difluoride
How do the lone pairs influence the bond angle
Lone pairs will repel more then bonding pairs
so the bond angle will be lower then a regular tetrahedral shape
What type of bond is formed when a molecule of BF3 reacts with a F- ion
A dative covalent bond
due to the lone pair on the F- donated to the B of the BF3
State the type of bond formed between the N atom and the B atom of F2HNBF3
It is a dative covalent bond
formed due to the lone pair on the N donated to the BF3
