Bonding Flashcards
What is a metallic bond?
The attraction between positive ions and delocalised electrons.
What is the structure of metals?
- The positive metal ions are packed close together in layers in a regular way.
- This three dimensional arrangement is called a giant metallic lattice.
- The metal ions are surrounded by delocalised electrons which move freely within the structure.
- Delocalised means not tied to a particular atom.
- Giant means endlessly repeating.
What is an ionic bond?
The electrostatic attraction between oppositely charged ions.
Describe ionic bonding.
- Ionic bonding occurs between metals and non-metals.
- Electrons are transferred from a metal to a non-metal.
- Positive and negative ions are formed.
- Metal atoms lose electrons and become positively charged.
- Non-metals gain electrons and become negatively charged.
What are the charges of compound ions?
+1:
- ammonium
-1:
- hydroxide
- nitrate (III)
- nitrate (V)
- cyanide
- hydrogen carbonate
- hydrogen sulfate
-2:
- carbonate
- sulfate (IV)
- sulfate (VI)
- hydrogen phosphate
-3:
- phosphate
What is a covalent bond?
A shared pair of electrons.
What is a coordinate bond?
A covalent bond in which both electrons of the shared pair come from the same atom.
What are the shapes and bond angles of molecules with only bonding pairs of electrons?
• 2 bond pairs, 0 lone pairs:
- Linear shape
- 180°
• 3 bond pairs, 0 lone pairs:
- Trigonal plainer
- 120°
• 4 bond pairs, 0 lone pairs:
- Tetrahedral shape
- 109.5°
• 5 bond pairs, 0 lone pairs:
- Trigonal bipyramidal shape
- 90° and 120°
• 6 bond pairs, 0 lone pairs:
- Octahedral shape
- 90°
Same goes for any double/triple bonds.
What are the shapes and bond angles of molecules with lone pairs of electrons?
• 2 bond pairs, 1 lone pair:
- V-shaped
- 117.5° (120 - 2.5)
• 3 bond pairs, 1 lone pair:
- Trigonal pyramidal
- 107° (109.5 - 2.5)
• 2 bond pairs, 2 lone pairs:
- V-shaped
- 104.5° (109.5 - 5)
• 3 bond pairs, 2 lone pair:
- Trigonal plainar
- 120°
• 4 bond pairs, 2 lone pairs:
- Square plainar
- 90°
What does electronegativity mean?
The power of an atom to attract the pair of electrons in a covalent bond.
What are the differences between non-polar covalent bonds and polar covalent bonds?
Non-polar covalent bonds:
- No or very small difference in electronegativity.
- Electron pair shared evenly.
- No dipole in bond.
- Electronically symmetrical.
Polar covalent bonds:
- A difference in electronegativity.
- Bonded electron pair is nearer the more electronegative atom.
- Electronically asymmetrical.
What makes a molecule polar/non-polar?
- A molecule is non-polar if it is electronically symmetrical as the bond dipoles cancel out.
- A molecule is polar if it is electronically asymmetrical as the bond dipoles don’t cancel out.
What are the three types of intermolecular forces and when do they occur?
• Van der Waals’ forces:
- Occur between all simple molecular substances with covalent bonds between atoms.
- Occur between atoms of noble gases.
• Permanent dipole-dipole forces:
- Only occur between simple molecules which have a permanent dipole.
• Hydrogen bonds:
- Only occur between simple molecules containing N—H, O—H or F—H bonds.
How do van der Waals’ forces work?
- Caused by the movement of electrons which unbalances the charge distribution within the molecule, creating an instantaneous dipole across the molecule.
- It is constantly forming and disappearing.
- This induces a dipole in neighbouring molecules, resulting in weak forces of attraction between molecules.
- Van der Waals’ forces are present between all simple molecules but they are only the only forces present between non-polar molecules.
How does permanent dipole-dipole forces work?
- These occur between molecules which have a permanent dipole.
- They occur in addition to van der Waals’ forces.
- The partial positively charged end of one molecule is attracted to the partial negatively charged end of a neighbouring molecule.
- Usually stronger than van der Waals’ forces.
How does hydrogen bonding work?
- Occurs between molecules which contain a hydrogen atom bonded to either F, O or N.
- A hydrogen bond is formed between a partial positively charged hydrogen atom and a lone pair of electrons on a N, O or F in a neighbouring molecule.
- They occur in addition to van der Waals’ forces.
- Hydrogen bonds are the strongest intermolecular force.
What must you show when drawing hydrogen bonds?
- Two molecules
- All lone pairs
- Partial changes
- Correct alignment of atoms
What are the properties of substances with hydrogen bonding?
- Higher boiling points than expected due to the strength of the hydrogen bonds between molecules.
- Substances which can hydrogen bond tend to dissolve in water because they form hydrogen bonds with water.
What are the anomalous properties of water?
- Ice is less dense than liquid water, so it floats.
- This also explains why water pipes can burst in winter as ice expands compared to liquid water zzz
- Water molecules are held in an open tetrahedral 3D lattice structure by hydrogen bonds.
Why is energy needed to change a substance from a solid to a liquid?
- Energy is needed to overcome the forces holding the particles together.
- The stronger the forces, the more energy is needed to overcome them, so the higher the melting point or boiling point.
What does electrical conductivity depend on?
- An electric current can only flow if there are charged particles which are free to move.
- Current can be carried by delocalised electrons or free ions.
What makes a substance soluble?
- If solute and solvent molecules attract each other.
- Ionic and polar substances dissolve in polar solvents such as water.
- Non-polar substances dissolve in non-polar solvents such as hexane.
What structure do ionic compounds have?
- Giant ionic lattice.
- The negative and positive ions alternate in the lattice. Each ion is surrounded by oppositely charged ions in all directions.
- The giant ionic lattice is held together by strong electrostatic forces of attraction between oppositely charged ions.
What are the properties of ionic compounds:
• High melting point:
- It takes a lot of energy to overcome the strong forces of attraction between the oppositely charged ions.
• Electrical conductivity:
- When solid, ionic solids do not conduct. The ions are fixed in position and cannot move to carry current.
- When dissolved or molten, they do conduct. Ions are free to move and carry current.
• Brittle:
- If enough force is applied the layers slide over each other.
- Like will charges move next to each other. causing repulsion and the lattice structure breaks down.
