Module 2 Chapter 6\ Flashcards
What are properties of a chemical bond
They have a definite direction and length
What do these properties mean
That molecules have a distinct shape
What determines the shape of a molecule
Repulsion between electrons in the outer shell determine its shape. The electron pairs repel so they are as far from each other as possible.
What is the order from least to most repulsive in electron pair repulsion theory
Bonded pair to bonded pair, bonded pair to lone pair, lone pair to lone pair
What are the rules in shape determination
Lone electron pairs repel greater than bonded pairs.
Lone and bonded pairs are involved in shape determination.
What is a multiple bond considered as in electron pair repulsion theory
It is considered as a single pair
What are the features of a tetrahedral structure
4 bonded pairs, 0 lone pairs
Bond angle - 109.5
What is an example of a tetrahedral structure
Methane
What are the features of a pyramidal structure
3 bonded pairs and one lone pair
Bond angle 107 degrees
What is an example of a pyramidal structure
Ammonia
What are the features of a bent structure
2 bonded pairs, 2 lone pairs
bent angle = 104.5
What is an example of a bent structure
Water
What are the features of a linear structure
Bond angle - 180*
What is an example of a linear structure
Carbon dioxide
What are the features of an octahedral structure
Bond angle 90*
Example of an octahedral structure
Sulfur hexafluoride
What are the features of a trigonal plantar structure
Bond angle 120*
they are all in the same plane
What is an example of a trigonal planear structure
Boron triflouride
What is the shape of carbonate and nitrate ions
They are trigonal planear
What is the shape of a sulfate ion
It’s tetrahedral
How do you represent the different bonds
Solid wedge - coming towards you (out of the page)
Dotted wedge - going away from you (into page)
normal line - in the plane of the page
What is electronegativity
The ability of an atom to attract the bonding electrons in a covalent bond
What is the scale that is used to measure electronegativity
The Qualitative Pauling scale gives a measure of electronegativity where the higher the number the higher the electronegativity
What is the general rule for electronegativity
It increases across the period and up a group (doesn’t include noble gases)
What are the 3 factors affecting electronegativity
Number of protons
Atomic radius
Electron shielding
How does number of protons affect electronegativity
The more protons you have in the nucleus the stronger the force of attraction
how does atomic radius affect electronegativity
The closer the bonding pair to the nucleus the stronger the attraction (as distance from nucleus increases the force of attraction decreases)
What is electron shielding and how does it affect electronegativity
Electron shielding is the repulsion of the bonding pair by electrons in the inner shells between the nucleus and bonding pairs, the more shells between the bonding pairs and nucleus the weaker the attraction is.
What affects whether the bond is ionic or covalent
If the difference in electronegativity is not that big. The electron won’t be taken completely like in ionic bonds.
What are non-polar bonds
They occur when the electron pair is shared equally. It’s when both elements bonded have the same electronegativity. In most cases this is due to them being the same element.
What are polar bonds
When one element in the molecule has a greater attraction for the bonded pair of electrons than the other elements. This leads to charge separation.
What is the symbol for the partial positive and negative charges
delta positive and delta negative
What forms as a result of bond polarisation
Permanent dipoles form as a result of bond polarisation.
What is a characteristic of dipoles
They have a direction and magnitude
What do polar bonds not always mean
polar bonds don’t always mean that the molecule is polar
What is the difference between a polar and non-polar molecule
Polar molecules have a net dipole movement (as the dipoles don’t cancel each other out). Whereas non polar molecules don’t have a net dipole movement (as the dipoles cancel each other out).
What are the three types of intermolecular forces
Permanent dipole - dipole interaction
Induced dipole - dipole interaction
Hydrogen bonds
Where are intermolecular forces present
They are only present between covalent molecules
What is the relative strength of an intermolecular force compared to a covalent bond
Covalent bond - strong
Intermolecular forces - weak
How is an instantaneous dipole formed
The electrons are mobile
The electrons have a negative charge
We could get a molecule with slightly more electrons on one side of the molecule than the other side of the molecule
So a dipole has spontaneously come into existence
What is an induced dipole
These dipoles are temporary
The movement of electrons produces a changing dipole in a molecule
At any instant, an instantaneous dipole will exist, but it’s position is constantly switching
The instantaneous dipole induces a dipole on a neighbouring molecule
The induced dipole induces a further dipole on a neighbouring molecule, which then attract on another.
What is a permant dipole interaction
They are within the molecules where the dipole within the molecule is fixed
The difference in electronegativity is so great that one is always pulling stronger than the other
An intermolecular force then forms between the positively dipole of one molecule and the negatively charged dipole of another molecule.
What is hydrogen bonding
A type of permanent dipole - dipole interaction
What are the conditions needed for hydrogen bonding to occur
One molecule has to contain a highly polarised H atom. The other molecule must have a small, electronegative atom, with lone pairs of electrons.
What is the property of hydrogen that allows this to happen
H is small and can get very close to the other small atom, hence the strong attraction.
What are metallic bonds
The strong electrostatic force of attraction between the sea of delocalised electrons and the positive metal cations in the lattice.
Where do the delocalised electrons come from
The delocalised electrons come from the outer shell of the metal, where it looses the electrons to form a full outer shell of electrons.
What causes metallic bonds to be stronger
The size of the positive charge on the ion
The size of the metal ion
The number of mobile electrons
