3.1 - 3.7 Bonding Flashcards
What is an ionic bond?
The electrostatic attraction between oppositely charged ions
Positive ion
Cation
Negative ion
Anion
What is a covalent bond?
A shared pair of electrons. The electron pair is attracted to both nuclei so resist separation.
What is a co-ordinate bond?
A covalent bond where both electrons in the shared pair originate from the same atom
What is metallic bonding?
The attraction between positive metal atoms and the surrounding delocalised sea of electrons
What is electronegativity?
The power of an atom to attract the pair of electrons in a covalent bond
Nuclear charge up = electronegativity ?
Electronegativity up
Atomic radius up = shielding ? = electronegativity ?
Shielding up = electronegativity down
What is used to measure electronegativity?
The Pauling scale
What happens to electronegativity across a period?
- Increases
- Same no. of energy levels BUT
- Increasing no. of protons/nuclear charge
- Decreasing atomic radius
What happens to electronegativity up a group?
- Increases
- Fewer energy level in use
- Less shielding
- Decreasing atomic radius
What is a polar molecule?
One in which the electron density across the whole molecule is unevenly distributed
What is a permanent dipole?
When one side of the molecule is permanently more negative, happens when a molecule is not symmetrical
What are the 3 main types of inter-molecular forces?
- Dipole-dipole interactions
- Hydrogen bonding
- Van der Waal’s forces
What are dipole-dipole interactions?
- Attractive forces between polar molecules
- Whatever their starting position, molecules will ‘flip’ to attract
What are hydrogen bonds?
- Not a bond, an inter-molecular force
- Only takes place when H bonded to O, F or N with at least one lone pair
What are Van der Waal’s forces?
- Also known as temporary dipole-induced dipole interactions
- Caused by the movement of electrons so the more electrons there are the stronger the force
- Exist between all molecules at all times, in addition to any other forces
List the three main inter-molecular forces from weakest to strongest
- Van der Waal’s
- Dipole-dipole
- Hydrogen bonding
Describe the particles in a solid
Regular, close, vibrate about a fixed position
Describe the particles in a liquid
Random, close, can move past each other
Describe the particles in a gas
Far apart, rapid and random motion
What is the name for the energy required to boil a liquid?
Enthalpy of vaporisation
What is the name for the energy required to melt a solid?
Enthalpy of fusion
What are the four types of crystal structure?
- Ionic
- Metallic
- Molecular (simple covalent)
- Macromolecular (giant covalent)
What is an ionic crystal?
Positive and negative ions held together in a giant ionic lattice by strong electrostatic attraction between oppositely charge ions
Describe and explain the melting points of ionic compounds
- High
- Strong electrostatic attraction between oppositely charged ions
Describe and explain the electrical conductivity properties of ionic compounds
- Does not conduct when solid
- No ions (charged particles) free to move
- Does conduct when molten or in solution
- Ions free to move and carry charge
Describe and explain the physical properties of ionic compounds
- Hard but brittle
- A force can move the ions and produce contact between like charges causing them to repel
Describe and explain the solubility of ionic compounds
- Often dissolve in water
- Ions become solvated and surrounded by water molecules
What is a metallic crystal?
A giant lattice of positive ions held together by a sea of delocalised electrons
Describe and explain the melting points of metals
- High melting and boiling points
- Strong electrostatic attraction between metal ions and delocalised sea of electrons
Describe and explain the electrical conductivity of metals
- Conduct in all states
- Delocalised electrons free to move and carry charge
Describe and explain the physical properties of metals
- Malleable and ductile
- Metal ions can slide past each other while retaining their lattice structure and metallic properties
Describe and explain the solubility of metals
- Insoluble in water
- Metallic bonds are too strong for water so overcome so metal ions cannot become solvated
What is a molecular crystal?
Individual molecules held together by weak intermolecular forces
Describe and explain the melting points of molecular solids
- Low melting points
- Weak intermolecular forces (VDW) do not require much energy to overcome
Describe and explain the physical properties of molecular solids
- Soft and easily breakable
- Weak intermolecular forces (VDW) do not require much energy to overcome
Describe and explain the electrical conductivity of molecular solids
- Never conduct electricity
- No charged particles free to move
What is a macromolecular crystal?
A giant arrangement of atoms joined by covalent bonds
Describe and explain the melting point of diamond
- Very high (3,000C +)
- Strong covalent bonds require a lot of energy to break
Describe and explain the physical properties of diamond
- Very hard
- Strong covalent bonds require a lot of energy to break
Describe and explain the melting point of graphite
- Very high (3,000C +)
- Strong covalent bonds require a lot of energy to break
Describe and explain the physical properties of graphite
- Soft, flaky and slippery
- Layers slide over each other because of delocalised electrons between layers
Describe and explain the electrical conductivity of graphite
- Conducts electricity
- Delocalised electrons free to move and carry charge
How does the bond angle change when a molecule’s loan pair forms a hydrogen bond?
- Increases
- Loan pair more like bonding pair so does not repel so strongly
How can electronegativity values be used to predict whether a given chloride is likely to be ionic or covalent?
Large difference in electronegativity = Ionic
Small difference in electronegativity = Covalent
Explain the formation of hydrogen bonding between protein molecules
- C=O and N-H bonds are polar
- O more electronegative than C, N more electronegative than H
- H-bonding between Hpartial+ and Opartial- of different molecules
- Using lone pair of electrons from oxygen
Why does the boiling point of fluorine compounds not fit into other trends?
- Unexpectedly high
- Due to hydrogen bonding
- Caused by large differences in electronegativity of fluorine and other element
Give an equation for a reaction in which a co-ordinate bond is formed
NH₃ + H⁺ → NH4⁺
Why is aluminium chloride covalent rather than ionic?
- Smaller electronegativity difference
- So more equal sharing
How do you know if two atoms will bond ionically of covalently?
Ionic = Big electronegativity difference
Covalent = Small electronegativity difference
How does hydrogen bonding work?
Hpartial+ attracted to lone pair of another partially negative molecule
Define polar bond
A bond where the bonding pair is shared unequally
Why does a lone pair of electrons repel more strongly than a bonding pair?
More compact
