Chemical Bonding Flashcards
Valency and ionisation energy rule
In order to remove electrons that are closer to the nucleus than the valence electrons, a lot more energy is needed, so if there is a big jump in IE in between the 3rd and 4th for example, it means the element has 3 valence electrons and is in group 3
Types of chemical bonding (3)
Ionic
Metallic
Covalent (pure and polar)
Electronegativity
The power of an atom to attract electrons to itself
Pure covalent bond electronegativity value
0 - 0.4
Polar covalent bond electronegativity value
0.5-1.9
Ionic bond electronegativity value
> 1.9
Factors that affect electronegativity (2)
Across the period
Down the group
How moving across the group affects electronegativity
As you move across the period, there in an increase in the number of protons which results in a greater nuclear charge and a larger electronegativity value
How moving down the group affects electronegativity
As we move down the group, the atomic radius increases along with the shielding effect resulting in a lower electronegativity value
Ionic bonding
The electrostatic attraction between oppositely charges ions (positively charged cations and negatively charged anions
Ionic bond properties (4)
High MP+BP - strong electrostatic forces between oppositely charged ions
Conducts if molten/aqueous - If solid the ions are in a fixed crystal lattice = can’t carry charge
Brittle
Soluble in polar solvents
Metallic bonding
Electrostatic attraction between positive cations and delocalised electrons
Properties of metallic bonds (3)
Malleable and ductile (due to non-directional bonds)
High conductivity (due to delocalised electrons)
High melting and boiling point(strong electrostatic force between cations and anions(the high the P number the more))
Covalent bonding
The electrostatic attraction between the nuclei of 2 atoms and shared pair of electrons
Polar covalent
When there is an unequal distribution of charge
Single bond (3)
(Single sigma (σ) bond)
Overlap of s-orbitals
Overlap of s and p-orbitals
Head to toe overlap of p-orbitals
Pi bond
Forms from the sideways overlap of p-orbitals
Double bond
1 σ (sigma) bond and 1 π (pi) bond
CAN ONLY FORM IF YOU HAVE A P VALENCE ELECTRON
Dative covalent bond
(Coordinate bond)
When a substance shares its lone pair of electrons with another substance, only occurs when an atom has an incomplete octet
Molecular shapes
Based on valence shell electron pair repulsion theory (VSEPR), electrons pairs need to be as far from each other as possible
Based on :
-no. of areas of negative charge
-lone pairs
Ions rule
Gained/lost by the central atom only
Pure covalent bond
No unequal distribution of charge
Dipole moment
Unequal distribution of charge
What determines if a molecule is polar (2)
Whether bond is polar or not
Molecule shape (symmetrical :i ndividual dipoles cancel each other out)
Polar and non-polar solubility rule
Like dissolves like
IMF vs bonds
IMF is between molecules, bonds is within molecules
Van Der Waals forces (3)
Hydrogen bonding
Pd-pd
Id -id
Hydrogen bonding
Strongest VDW force, when H is directly bonded to N O F
Hydrogen bonding is a special case of permanent dipole - permanent dipole force between molecules where hydrogen is bonded to a highly electronegative atom
Pd-pd
Permanent dipole-permanent dipole
2nd strongest VDW that occurs between polar molecules
Carbon to N, O, halogens,
Hydrogen to Cl and Br
Id-id
Instantaneous dipole - induced dipole/ London dispersion
Non-polar molecules
Weakest VDW, thenmore electrons the stronger
Anomalous properties of water (3)
Due to high no of hydrogen bonds:
-relatively high MP+BP
-relatively high surface tension
Low density of the solid ice compared with water
Surface tension
The tendency of molecules of a liquid to be attracted more towards one another at the surface of the liquid than to the air above it
Buckminsterfullerene
C60, buckyballs
Carbon molecule made up of 60 atoms arranged like the faces of a soccer ball (pentagon and hexagons). Simplest of a family of similar nanoparticles known as fullerenes
Covalent radius of a carbon atom
0,077 nm
Nanoparticles
Usually have sizes in the range of 1-100nm (1nm is 10-9 metres)
Properties/characteristics of buckminsterfullerene (4)
Due to van der Waals dispersion IMF forces, it has a lower Mp than diamond/graphite
Sublimes at 800k (527*C) vs Diamond and graphite at 4000K
Insoluble in water but slightly soluble in organic solvents (benzene/methylbenzene)
More slippery than Teflon (PTFE -poly(tetrafluoroethene))
Solubility of C60
(Buckminsterfullerene)
Insoluble in water since it can’t for hydrogen bonds with it
Slightly soluble in organic solvents eg. Benzene since it forms van der Waals attractions with them
Carbon nanotube
Single sheet of carbon atoms which make up graphite (graphene) rolled up
Characteristics of nanotubes (5)
-Have a diameter of about 1nm, can be very long. Individual tubes are very strong and stiff due to strong covalent bonds between atoms making up the tubes
-Van Der Waals forces between individual tubes is weak so bulk material isn’t so strong
-May be open ended or capped one side/both by half a Bucky ball
-Delocalised electron suggests they should be good conductors of electricity (can achieve by changing the way they are made)
-Delocalised electrons also shows that they are good conductors of heat (transferred via electron movement. Conductivity is good along the tube, not across.
Structure of graphene
Single sheet from a graphite structure, 2D
Extends indefinitely in both dimensions
Stacking them would give you graphite
Giant metallic bond properties(3)
Malleable/ductile due to non-directional bonds
High MP+BP due to strong electrostatic forces
Good conductor of electricity due to delocalised electrons
Giant ionic bonds
Giant ionic bond properties (3)
Brittle
Conducts electricity when molten/aqueous
High MP+BP due to strong electrostatic forces
Giant covalent bond properties (
Giant covalent bond properties (
