Alevel Chemistry - Topic 2 Flashcards
What is an ion?
A charged particle formed when an atom or group or atoms has lost, or gained, one or more electrons
What are Cations?
Positively charged ions
What are anions?
Negatively charged ions
What is true about isoelectronic species?
Same number of electrons hence they have the same electronic configuration
Which experiment provides evidence for ions?
Electrolysis provides evidence for ions because it represents the migration of ions either to the cathode (-) or the anode (+)
What is ionic bonding?
Electrostatic forces of attraction between oppositely charged particles to form an ionic bond
What is the trend of ionic radius down a group?
Increases
What is, and explain, the trend of ionic radius across isoelectronic ions?
- As the atomic number increases
- The effective nuclear charge increase since all species have same number of electrons
- The attraction between their nucleus and electrons increase
- The ionic radius decreases
What is charge density and how does this affect the bond?
Charge density is a measure of the charge/size ratio. Ions with a high charge density form stronger bonds than those with a low charge density
What factors affect the strength of an ionic bond?
Strength increases when:
- There is an increase in ionic charge
- Decrease in ionic radius
Charge density has to be high*
Why might the ionic bond between F- and Mg2+ be stronger than that if it was Li+
The sizes of lithium and magnesium ions are similar but magnesium ions have a higher charge. This means that magnesium ions have a higher charge density and are more strongly attracted to the Fluoride ions.
What is a covalent bond?
The strong electrostatic forces of attraction between two nuclei and the shared pair of electrons between them
Draw the two structures of sigma bonds?
The end on overlap between p or s orbitals.
What the structure of a Pie bond or otherwise known as the double bond?
Sideways overlap of P orbitals
What is a dative covalent bond?
When an orbital with a lone pair of electron in one atom overlaps with a vacant orbital in another atom
What must be shown when drawing a dative convent bond dot-cross?
- Represented by an arrow from the atom providing the electron pair towards the atom with the vacant orbital
- If present, charge brackets must be shown to show polytomic ions
- Dots and crosses must be correctly shown, where two dots or crosses must be present in the same dative bond to show its coming from a single atom
What is bond length?
The distance between the nuclei of two atoms that are covalently bonded together.
How is bond strength measured?
Given by the bond enthaply for a particular covalent bond but note this changes with the environment a molecule is in.
What is bond enthalpy?
The enthaply change when pone maple of a bond in gaseous state is broken in Kj/mol
Explain the trend in bond strength of halogens? And what’s the exception?
- Down the group, the bond strength decreases.
- This is because the bond length increases
- so the halogen-halogen bond becomes weaker
*The exception to this is Florine since it is weaker than chlorine but has a shorter bond length. This is because its lone pairs of electrons are lose enough to produce a lot of repulsion
Explain the trend between strength of C triple bond, C double bond, and C single bond?
- As the number of bonds decreases, the bond length increases
- This causes the the bond strength to decrease since the electrostatic attraction between the two nuclei and the shared electrons is decreased
What dictates the shape of a molecule?
- The arrangement of electron pairs around the central atom keeps repulsion to a minimum
From a tetrahedral shape, how much is the angle reduced by when a lone pair is added?
109.5 - y2.5
Draw the structures:
- Linear
- trigonal planar
- Tetrahedral
- trigonal pyramidal
- trigonal bipyramidal
- Octahedral
- V shaped
- 180
- 120
- 109.5
- 107
- 90/120
- 90
- 104.5
