Flashcards in Bonding And Shapes Of Molecules Deck (49):
What are intramolecular bonding forces?
Forces of attraction between atoms within a molecule
What are intermolecular bonding forces?
Forces of attraction between neighbouring molecules
Give examples of intramolecular bonding
-polar covalent bonding
What is covalent bonding?
Sharing of or more pairs of electrons between two atoms
What is polar covalent bonding
Unequal sharing of one or more pairs of electrons by two atoms
What is ionic bonding?
Electrostatic force of attraction between oppositely charged ions
What are weak Van Der Waals forces?
Temporary dipoles in molecule attracting/repelling temporary dipoles in next molecule
What are permanent dipole-dipole attractions
Permanently polarised molecules attract polarised neighbour, where opposite ends attract
What is hydrogen bonding?
Permanently polarised molecules which have hydrogen and one of the elements N, O or F
What is electronegativity?
It’s the relative attraction an atom has for shared pairs of electrons in a covalent bond
Use electronegativity values to predict the type of bonding in
i) pure covalent
ii) polar covalent
0 - 0.7 - 1.7
cov - pol cov - ionic
Explain why potassium chloride has a much higher boiling point than phosphine (PH3)
Phosphine is held together by weak Van der Waals forces whereas potassium chloride is held together by ionic bonds
Phosphine is virtually insoluble in water, whereas the corresponding hydride of nitrogen which is in the same group as phosphorus is very soluble in water, how so?
The corresponding hydride is NH3, which contains a lone pair making the whole molecule polar covalent [electronegative differences]
This results in bonding with water and therefore dissolves in water
Phosphine is non polar and has little/no attraction to the water
What is water of crystallisation?
It’s water chemically combined in definite proportions in a crystalline compound
Give two uses of noble gases
Helium - in blimps
Argon - in light bulbs
What is the octet rule?
Atoms on reaction tend to reach an electronic arrangement with eight electrons in their outermost shell
What are the exceptions to the octet rule?
Beryllium and Boron - few electrons in their outer levels so they cannot gain enough electrons to reach eight
D block elements
What is valency?
Number of bonds an atom of an element forms when it reacts
What group of elements have variable Valencies and give an example
Iron - 2,3,6
Copper - 1,2
What do metal atoms become when they lose one or more electrons?
Positively charged - Cation
How is a cation smaller than the corresponding atom?
It has lost electrons and is positively charged and therefore lost a shell
Characteristics of Ionic Substances
Form crystal lattices
High melting and boiling points due to strong forces of attraction
Soluble in water
Conduct electricity in molten/aqueous state
Give examples of ionic materials in everyday life
Salt tablets - to replace salt lost in sweating
Brine - curing bacon
What factors dictate the extent to which the shared electrons are attracted by different nuclei?
Size of the Atom - smaller atom have a stronger attraction because they can get closer to electrons
Nuclear charge - atoms with bigger nuclear charge will have greater attraction for the shared electrons
Characteristics of Covalent Bonding
Low melting and boiling points - gases at room temperature due to weak intermolecular forces
Do not conduct electricity due to the fact they consist of neutral molecules
Do not dissolve readily in water
Give examples of polar materials in every day life
Water - washing clothes
Glucose - lucozade
Give examples of non - polar materials in every day life
Account for the general trend of electronegativity across a period
-nuclear charge inc, positive attractive force on electrons
-atomic radius decreases as electrons are pulled in more tightly
Account for the general trend of electronegativity down a group
-extra levels means there is extra screening
-atomic radius inc caused by extra energy levels means electrons aren’t as tightly held and no attracted as strongly
Distinguish between a sigma and a pi covalent bond
Sigma - end on overlap of orbitals
Pi - sideway overlap of p orbitals
What does the electron repulsion theory state?
Electron pairs in outer shell of central atom repel each other and end up as far apart as is geometrically possible
Lone pairs have a greater repelling effect than bonding pairs
What are the posible shapes sit molecules of general formula : AB2
Valency = 2
Account for the difference in shape of NH3 and BF3
NH3 - three bond pairs and one lone pair
BF3 - three bond pairs
Describe the bonding in the nitrogen molecule in terms of sigma and pi bonding
Sigma = 1
Pi = 2
What type of intermolecular forces would you expect to find in nitrogen gas? Explain your answer
Van Der Waals, it is non polar
If a molecule contains two bonds, what shapes can it be?
No lone pairs - Linear
Lone pairs - V-shaped
If a molecule contains three bonds, what shapes can it be?
No lone pairs - Trigonal Planar
Lone pairs - Pyramidal
If a molecule contains four bonds, what shapes can it be?
Lone pairs - Tetrahedral
What bond angle does linear have?
What bond angle does v shape planar have?
What bond angle does trigonal planar have?
What bond angle does pyramidal have?
What bond angle does tetrahedral have?
Identify in ammonia, the type of intermolecular bonding and intermolecular forces present
Intramolecular - polar covalent bonding
Intermolecular - hydrogen bonds
What is the molecular formula of benzene
Account for the difference in the shapes of BF3 and NH3 molecule
Boron - three bond pairs
Nitrogen - three bond pairs and one lone pair
How do you know how many sigma and pi bonds there are?
Every element forms only a single covalent bond. That is sigma bond. If there are 3 bonds, one must be covalent and other 2 pi
Look at valency to see how many bonds
What is bond energy?
Its the verage energy required to break a bond and seperate atoms in gaseous state