CH2 - Bonding (1)
- Created by: beth-marie2511
- Created on: 28-03-16 22:04
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- CH2 - Bonding (1)
- Chemical Bonding
- Ionic Bonding
- Ions form when atoms lose or gain electrons.
- Positive ions form through electron loss.
- Negative ions form through electron gain.
- The Ionic Bond is the attraction between the positive and negative ions.
- Generally ionic compounds contain a metal ion.
- Certain amount of repulsion between ions of the same charge.
- This is minimised by the ions arranging themselves so that they are close only to those of an opposing charge.
- This attraction outweighs any repulsion.
- This is minimised by the ions arranging themselves so that they are close only to those of an opposing charge.
- Ionic bonds are electrostatic attraction between oppositely charged ions.
- E.G. Na2+ O-
- E.G. Li+ F-
- Ionic compounds exist as Giant Ionic Lattices.
- Properties
- Crystalline solids.
- High melting point
- High boiling point.
- Soluble in water.
- Electrical conductors when molten or in aqueous solution.
- Properties
- When drawing diagrams to represent ionic bonding only show the outer shells.
- Show the atoms before and after electron transfer.
- Dot & Cross Diagrams.
- Ions form when atoms lose or gain electrons.
- Covalent Bonding
- Occurs when 2 atoms share a pair of electrons between them.
- Electrons involved occupy the same orbital but have different spins.
- Some repulsion will occur.
- The attraction of each nucleus for the shared electron pair is the covalent bond.
- This attraction is greater than the repulsion between the bonding pair of electrons.
- 2 atom can be the same or different.
- This is why some covalent substances are elements while others are compounds.
- Electrons involved occupy the same orbital but have different spins.
- Covalent bonds are a shared pair of electrons between two atoms.
- E.G. C02
- E.G. H2O
- Results in the formation of simple molecules.
- Also results in the formation of macromolecules.
- Occurs when 2 atoms share a pair of electrons between them.
- Coordinate Bonding
- A type of covalent bonding as the bond is a shared pair of electrons between 2 atoms.
- A coordinate bond is a covalent bond in which both shared electrons originate from the sae atom - the donor atom.
- E.G. Coordinate bonding of NH3 molecule.
- On the nitrogen atom there is a pair of electrons that have not been used in bonding.
- This is a lone pair of electrons.
- These electrons can be donated to an electron deficient atom to form a coordinate bond.
- An example of an electron deficient atom is Boron Trifluoride.
- There are only 6 electrons in the outer shell of the boron atom so a donor atom is required to donate a pair of electrons and form a coordinate bond.
- An example of an electron deficient atom is Boron Trifluoride.
- On the nitrogen atom there is a pair of electrons that have not been used in bonding.
- Ionic Bonding
- Electro - negativity and Polar Bonds
- Electro - negativity is the ability of an atom to attract the shared pair of electrons in a covalent bond.
- Electro - negativity decreases as you travel down a group.
- This is because the increasing nuclear charge is greatly outweighed by the distance of the outer shell from the nucleus.
- Electro - negativity increases as you move across periods.
- Higher value of electro -negativity on the right side of the periodic table.
- Group 0 is ignored because those elements do not form bonds.
- Fluorine is the most electro - negative element.
- The larger the numerical value the more electronegative that element is.
- Electro - negativity decreases as you travel down a group.
- Polarisation of Covalent Bonds
- e.g. Cl-Cl
- Identical values = same electro - negative value.
- Both atoms have an equal attraction for the electron pair that makes the covalent bond.
- Therefore the bonding electron pair is exactly halfway between both atoms when drawn.
- This is a non-polar bond.
- e.g. HCl
- Cl has a higher electro - negativity than H.
- This makes the Cl more able to attract the shared pair of electrons than H.
- Shared electron pair is closer to the Cl atom than the H when drawn.
- This is a polar bond.
- It is the difference in the electro - negativities of the two bonded atoms that will influence the amount of ionic or covalent character that the resulting bond posseses.
- A small difference between the values would suggest that the electron pair is more equally shared.
- A large difference in the two values would suggest a more polar bond - one atom has a greater ability to attract the electron pair.
- Not all covalent bonds between two different atoms will be considered as polar.
- The more polar the bond the greater the partial negative and positive charges of each atom.
- e.g. Cl-Cl
- Electro - negativity is the ability of an atom to attract the shared pair of electrons in a covalent bond.
- Forces Between Molecules
- Intermolecular Forces
- Forces between molecules
- Hugely influence the physical properties of substances including: melting point, boiling point, solubility and volatility.
- 3 Types
- Permanent Dipole
- Molecules that contain a permanent polar bond attract each other this way.
- Exist permanently because of the differences in electro-negativity of the atoms involved in the bond.
- Stronger than Induced Dipole to Induced Dipole attractions.
- This is because these bonds are permanent.
- Induced Dipole
- Induced = made to happen
- A very weak force that exists between all single atoms and molecules.
- Occur because of electron movements within the atom / molecule.
- E.G. He (Helium)
- Helium has an extremely low melting point meaning that the forces between the atoms are very weak.
- If solid He at 273 degrees (0K / absolute zero) is warmed by one degree it melts.
- This means enough energy has been supplied to overcome the forces between the atoms.
- If solid He at 273 degrees (0K / absolute zero) is warmed by one degree it melts.
- Helium has an extremely low melting point meaning that the forces between the atoms are very weak.
- What is the reason for the need of energy to break the forces?
- Each He atom contains 2 electrons in constant motion - at any instant they could both be on one 'side' of the atom.
- This makes one 'side' of the atom slightly positive and the other slightly negative.
- This is an INDUCED DIPOLE
- Another He atom will have an induced dipole 'set up' causing the two to attract one another.
- This makes one 'side' of the atom slightly positive and the other slightly negative.
- E.G. He (Helium)
- Helium has an extremely low melting point meaning that the forces between the atoms are very weak.
- If solid He at 273 degrees (0K / absolute zero) is warmed by one degree it melts.
- This means enough energy has been supplied to overcome the forces between the atoms.
- If solid He at 273 degrees (0K / absolute zero) is warmed by one degree it melts.
- Helium has an extremely low melting point meaning that the forces between the atoms are very weak.
- Each He atom contains 2 electrons in constant motion - at any instant they could both be on one 'side' of the atom.
- A dipole is a separation of charge so that one end of the particle is positive and the other is negative.
- The induced dipole - induced dipole attractions are stronger between chlorine atoms than He atoms because there are more electrons in the chlorine atom therefore the dipoles are stronger.
- Therefore chlorine has the higher melting / boiling points because more energy is needed to overcome the ID - ID.
- On descending group 7 the melting / boiling points increase because of the increasing number of electrons in each element so there are a greater number of ID - ID attractions.
- Hydrogen Bonding
- The strongest type of permanent dipole - permanent dipole attraction.
- Strongest type of intermolecular force but is only 10% the strength of a covalent bond.
- Occurs between molecules that contain H bonded to one of the three most electro-negative elements - N, O & F
- If a molecule contains one of these bonds:
- H - O
- H - F
- H - N
- It will be able to 'hydrogen bond' to a similar molecule.
- If a molecule contains one of these bonds:
- When bonded to N, O or F the two bonding electrons are held so closely to the more electro-negative atom H exists almost as a bare proton because it has only one electron..
- The Influence of Hydrogen Bonding on Boiling Point
- The strength of the the Van Der Waals forces increases with increasing Mr.
- As molecules increase in Mr so does the boiling point.
- This is because there are a greater number of electrons present in larger molecules.
- HF, H2O and NH3 all have much higher boiling points.
- This is because of these molecules having a far stronger attraction between them.
- This increased attraction is caused by hydrogen bonding.
- This is because of these molecules having a far stronger attraction between them.
- The strongest type of permanent dipole - permanent dipole attraction.
- Permanent Dipole
- Forces between molecules
- IntramolecularForces
- Forces within molecules
- E.G Covalent bonds
- Forces within molecules
- Intermolecular Forces
- Chemical Bonding
- When drawing diagrams to represent ionic bonding only show the outer shells.
- Dot & Cross Diagrams.
- Covalent Bonding
- Occurs when 2 atoms share a pair of electrons between them.
- Electrons involved occupy the same orbital but have different spins.
- Some repulsion will occur.
- The attraction of each nucleus for the shared electron pair is the covalent bond.
- This attraction is greater than the repulsion between the bonding pair of electrons.
- 2 atom can be the same or different.
- This is why some covalent substances are elements while others are compounds.
- Electrons involved occupy the same orbital but have different spins.
- Covalent bonds are a shared pair of electrons between two atoms.
- E.G. C02
- E.G. H2O
- Results in the formation of simple molecules.
- Also results in the formation of macromolecules.
- Occurs when 2 atoms share a pair of electrons between them.
- Show the atoms before and after electron transfer.
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