M2 - Chemical Bonding (1) Flashcards
Electron structure, Ionic bonding and structure and Covalent bonding.
State what is meant by the term ionic bond [1].
Electrostatic attraction between positive and negative ions ✔
*Ionic bonding occurs between a metal and non-metal *
Describe what is meant by the term ionic lattice, in terms of the type and arrangement of particles present [2].
Repeating pattern ✔
of oppositely charged ions ✔
What is the result of ions attracting oppositely charged ions in all directions?
Giant ionic lattice (e.g. NaCl)
What happens to the melting / boiling points for giant ionic lattices, when the ionic charges increase in NaCl to MgO?
Melting / boling point increases as there is a stronger attraction between ions of Mg2+ and O2- than Na+ and Cl-
Are ionic compounds soluble?
Yes, they dissolve in polar solvents such as water / Alcohols
Can ionic compounds conduct electricity in solid, liquid or aqueous states, explain why
Na2O conducts electricity when molten or in aq solution and not when solid ✔
Molten Na2O has ions which are mobile ✔
Solid Na2O has ions which are fixed (in position) OR ions are not mobile ✔
Summarise the properties of most ionic compounds
High melting and boiling points.
Dissolve in polar solvents such as water.
Conduct electricity only when molten or dissolved in aqueous solution.
Draw a ‘dot-and-cross’ diagram to show the bonding in solid barium chloride. Show outer electrons only [2].
Draw a ‘dot-and-cross’ diagram to show the bonding in sodium sulfide. Show outer electrons only [2].
Draw a ‘dot-and-cross’ diagram to show the bonding in MgBr2. Show outer electrons only [2].
What is meant by the term covalent bond [1].
Shared pair of electrons ✓
Covalent bonding occurs between non-metals
What is a dative covalent bond? Provide an example of a compound that has a dative covalent bond
The shared pair of electrons has been supplied by one of the bonding atoms only.
The N atom on the ammonia molecule (NH3) donates its lone pair of electrons to an H+ ion forming an ammonium ion, NH4+.
What is a multiple covalent bond? Provide some examples
Two atoms share more than one pair of electrons:
Draw a ‘dot-and-cross’ diagram to show the bonding in a nitrogen molecule. Show outer electrons only [1].
Na2CO3 contains the carbonate ion, CO32−, shown below.
Draw the ‘dot-and-cross’ diagram for the carbonate ion.
Show outer electrons only and use different symbols for electrons from C and O, and any ‘extra’ electrons [2].
The displayed formula of a phosgene molecule is shown below.
Draw a ‘dot-and-cross’ diagram of a phosgene molecule, COCl2.
Show outer electrons only [1].
Define the term average bond enthalpy (ABE)?
The energy needed to break one mole of bonds in the gaseous state (kJ mol-1)
Larger the ABE value, the stronger the covalent bond
Describe the bonding and structure in graphite.
Explain why graphite is a good conductor, a soft material and has a very high melting point [5].
Giant covalent lattice Arranged in layers Good conductor - mobile electrons High melting point - covalent bonds have to be broken Soft - weak forces between the layers
State what is meant by the term metallic bonding? [2]
Electrostatic attraction between delocalised electrons and the positive ions
The melting points of the Period 3 metals sodium and magnesium are shown below.
Explain the differences in the melting points of sodium and magnesium, using the model of metallic bonding [3].
Magnesium has more outer OR bonding electrons ✓
Magnesium ions have a greater (positive) charge (density) ✓
Magnesium has a greater attraction between ions and delocalised electrons ✓
Magnesium has metallic bonding and is a good conductor of electricity.
Describe, with the aid of a labelled diagram, the metallic bonding in magnesium and explain why magnesium conducts electricity.
Include the correct charges on the particles in your diagram [3].
Diagram with regular arrangement of labelled ‘Mg2+ ions’ OR ‘2+ ions’
AND attempt to show electrons ✓
Labelled electrons between other species AND statement anywhere of delocalised electrons (can be in text or in diagram) ✓
Electrons move ✓
On a mini-white board / scrap piece of paper draw out the bond angles table, with the headings: number & type of electron pairs, electron-pair repulsion theory, shape, bond angle/o & name
What does molecular shape depend on?
Electron pairs around the central atom: bonded and lone pairs of electrons
In what way do electron pairs interact?
They repel each other
Which type of pair repels the most?
Lone pairs
What is the name of the way to predict a molecule’s shape?
Electron pair repulsion theory
Predict the shape and bond angle in a molecule that has 2 bonding pairs and 2 lone pairs around a central atom.
A Linear, 180°
B Non-linear, 104.5°
C Tetrahedral, 109.5°
D Trigonal planar, 120° [1]
Answer: B
Predict the bond angle in an F2O molecule and explain using the electron pair repulsioin theory [3].
Non-linear: 104.5 ✓
There are 2 bonded pairs and 2 lone pairs ✓
Lone pairs repel more than bonded pairs ✓
Name the shape of the ammonia molecule (NH3) and why ammonia has this shape and a bond angle of 107° [3]
Pyramidal ✓
There are 3 bonded pairs and 1 lone pair ✓
Lone pairs repel more than bonded pairs ✓
Why does a water molecule have a different shape to a carbon dioxide molecule? [2]
Electron pairs repel and get as far apart as possible
Oxygen in H2O has 2 bonded pairs and 2 lone pairs
Carbon in CO2 has 2 bonded pairs (2 double bonds)
What do dotted wedges, solid wedges and filled wedges stand for?
Why does ammonium chloride not conduct electricity when solid but does when dissolved in water? [1]
Ions cannot move in a solid
Ions can move in solution
What shape name and bond angle is given to a molecule with three bonded pairs & one lone pair?
Pyramidal & 107o
What shape name and bond angle is given to a molecule with two bonded pairs and two lone pairs?
Non-linear & 104.5o
What shape name and bond angle is given to a molecule with 2 bonded pairs around the central atom?
Linear & 180o
What shape name and bond angle is given to a molecule with 3 electron pairs and no lone pairs around the central atom?
Trigonal planar & 120o
What shape name and bond angle is given to a molecule with no lone pairs but four bonded pais?
Tetrahedral & 109.5o
What shape name and bond angle is given to a molecule with 6 electron pairs and no lone pairs around the central atom?
Octahedral & 90o
i. Predict the different shapes of, and bond angles in, NF3 and BF3 molecules [2].
ii. Explain why NF3 and BF3 molecules have different shapes and bond angles [2].
NF3 has 3 bonded pairs AND 1 lone pair (of electrons) AND lone pairs repel more (than bonded pairs) ✓
BF3 has three bonded pairs (of electrons) ✓
State the shape of, and F—S—F bond angle in, an SF6 molecule [2].
Octahedral ✓
90° ✓
Complete Table 6.1 to predict bond angles a and b and name the shapes which makes these bond angles in the functional groups of carboxylic acids and sulfonic acids [2].
