Please enable JavaScript.
Coggle requires JavaScript to display documents.
AS Chemistry- What do I know about bonding? (Section B: Polarity (You can…
AS Chemistry- What do I know about bonding?
Section F: Simple Molecular Structure
Simple Molecular Structure:
Weak intermolecular (Van der Waals) forces and strong covalent bonds causes the compound to have a low boiling and melting point as it does not require as much energy to break and overcome these forces.
They do not have free delocalised electrons. Therefore, they cannot conduct electricity.
Most of the compounds that have a simple molecular structure are insoluble in water, depending on their polarity. The more polar the covalent, the bigger the tendancy for water molecules to be attracted to them.
A molecule is made up of 2 or more atoms from the same or different elements bonded together.
Most compounds that are made up of a simple molecular structure are in the form of a gas or liquid at room temperature. This is because they have a low boiling and melting point due to their weak Van der Waals forces or the intermolecular forces.
Section A: Shapes of Molecules and IMFs
VSEPR (Valence Shell Electron Pair Repulsion) Theory explains how the shape of a molecule is determined by the number of electron pairs in its outside shell and whether these electron pairs are bonding or non-bonding.
Structures
V shaped Structure has a general formula of AX2. It has 2 bonding pairs and 2 lone pairs. Each angle between each bond is 104.5 degrees. An example of a compound that has a linear structure is Water. (H2O) Images of structures can be found in:
My table
Linear Structure has a general formula of AX2. It has 4 bonding pairs and no lone pairs. Each angle between each bond is 180 degrees. An example of a compound that has a linear structure is Carbon Dioxide. (CO2) Images of structures can be found in:
My table
Triagonal Planar has a general formula of AX3. It has 3 bonding pairs and no lone pairs. Each angle between each bond is 120 degrees. An example of a compound that has a linear structure is the compound BF3. Images of structures can be found in:
My table
Trigonal Pyramidal Structure has a general formula of AX3. It has 2 bonding pairs and 1 lone pair. Each angle between each bond is 107 degrees. An example of a compound that has a linear structure is the ionic compound of Ammonia (NH3). Images of structures can be found in:
My table
Triagonal Bipyramidal Structure has a general formula of AX5. It has 5 bonding pairs and no lone pairs. Each angle between each bond is 180 degrees or 90 degrees, depending on the position of each atom to the central atom. An example of a compound that has a linear structure would be PCl5. Images of structures can be found in:
My table
Tetrahedral Structure has a general formula of AX4. It has 4 bonding pairs and no lone pairs. Each angle between each bond is 109.5 degrees. An example of a compound that has a linear structure is Methane (CH4). Images of structures can be found in:
My table
There are types of intermolecular force. 1) Dipole-Dipole forces, 2) Van der Waals forces, 3) Hydrogen Bonding.
Dipole forces act between a molecule of 2 different polarity to have a dipole moment. Dipole-Dipole forces act between molecules that have permanent dipole moment. In an HCl molecule, Chlorine is more electronegative than hydrogen. This causes the electrons to be pulled towards the chlorine atom rather than the Hydrogen and therefore has a dipole.
Van der Waals forces are the forces that act as weak electrostatic attractions between all atoms and molecules that have opposite charges (dipoles). Temporarily at instant moment due to the electron movement. Example can be found
here
Dispersion forces are also known as instantaneous dipole-dipole. A symmetrical molecule like hydrogen doesn't seem to have any electrical distortion, but that is only on average. In real life hydrogen, shown by the lozenge, can have electrons on one side making that side negative and the other side positive.
Weak intermolecular (Van der Waals) forces and strong covalent bonds causes the compound to have a low boiling and melting point as it does not require as much energy to break and overcome these forces.
Hydrogen bonding is a special type of intermolecular force which is a combination of both covalent and dipole-dipole forces. It requires an atom with a high electronegativity with a lone pair, bonded covalently with a Hydrogen atom. The Hydrogen is sandwiched between the 2 atoms with high electronegativity.
Section B: Polarity
Electronegativity of an atom increases as you go along a period in the periodic table but decreases as you go down a group. The elements that has higher electronegavity (the element in the top right corner of the periodic table) will tend to make covalent bonds with the less electronegative element (on the bottom left corner of the periodic table).
The more electronegative an element is, the more polar the atoms.
Electronegativity is the tendency of an atom to attract a bonding pair of electrons in a covalent bond. Electronegativity increases as you go down a group and along a period as there will be gradually more protons, resulting in a smaller atomic radius. Fluorine, Nitrogen and Oxygen are most electronegative in the periodic table.
You can determine the type of bond between two atoms by calculating the difference in electronegativity values between the elements. The bigger the electronegativity difference the more polar the bond.
If the difference is between 0 and 0.4, it is a non-polar covalent. 0.5 to 1.9 would make it a polar covalent. Anything else above would be ionic (non polar)
Polar covalent is the unequal sharing of electrons between 2 elements. They have a difference in electronegativity in between 0.5 to 1.9. The highest will have a bigger tendancy to attract the charge delta minus.
A non-polar covalent is the equal sharing of electrons between 2 elements. They have a difference in electronegativity between the values 0 and 0.4.
Ionic bonding is the bond that forms between atoms that have the tendency to gain or lose whole electrons. The atoms with higher electronegativity will gain the electron. The difference of the electronegativity between the ions will be 2 or above.
Dative covalent bonds form when only one atom shares the pair of the electrons with another atom.
We know ions exist as current can flow through Sodium Chloride solution or any ionic solution due to the fact that the ions are free to move when it's is aqueous form or when these compounds dissolve in a solvent to produce the ions.
Electron density maps can tell us the electronegativity of atoms in a compound. This can easily tell us if they're polar as the atoms with higher electronegativity will appear with higher electron density on the map, forming polar covalent bonds.
"Explain the polarisation as applied to ions" Happens when an ion give a lone pair of electrons to a covalent atom to form a coordinate bond.
The table for the range of electronegativity values and their relation to the type of bonding can be seen
here
Section C: Dots & Cross Diagrams representing ionic and covalent bonding
Elements that can share electrons with other atoms of other elements that does not have a full outer shell with a condition that the difference of the electronegativity between these 2 elements is the values less than 2.
The covalent bond in an oxygen molecule is always a double bond because it has 2 lone pairs and 2 electrons that are ready to be shared . It is also very electronegative, meaning it has a bigger tendency than most other elements to attract electrons.
Dot and cross diagram of CO2
Dot & Cross Diagram Of Sodium Sulfide
Charge on an aluminium ion is 3+. Nitride ion is 3-
Elements that have difference in electronegativity that is more than 2 will form ionic bonds when reacted together.
Section D: Metallic bonding and giant metallic structure
Metallic bonding is a lattice that consists of positive ions existing in a "sea" of outer electrons.
Magnesium metallic bonding diagram
Metals are malleable because the layers of cations that slide over one another.
Metals are good conductors of electricity as they have a sea of delocalised electrons to carry the current for them.
Section E: Giant ionic and covalent structures
Giant covalent structure is a lattice that consists A LOT of non metal atoms. Each of them joined together by very strong covalent bonds in a continuous regular pattern which that's what would give the substance or compound to have a high B.M.P
Example: Diamond and graphite
It has weak intermolecular forces and very strong covalent bonds. This gives it a high melting boiling point so it would require a large amount of energy to overcome these forces.
The giant ionic structure is a type of structure that consists of ions that are arranged in a regular lattice pattern. They are connected to one another by ionic bonds between the positively charged ions and the negatively charged ions.
They only conduct electricity when melted as the ions will be free to move to carry the current. As the ionic bond breaks and seperate, individual separate ions will occur and will be free to move and carry the electric energy within the solution.
3D Diagram for sodium chloride.