Week 4 (Claire) Flashcards
What is the difference between Theoretical, Actual, and Percent Yields?
Theoretical Yield = the amount of product predicted by stoichiometry.
Actual Yield = the quantity of desired product actually formed.
Percent (%) Yield = Actual Yield / Theoretical x 100
What are some examples for not achieving 100% yield?
Side reactions may occur that produce undesired products.
Incomplete reaction due to poor mixing or reaching equilibrium.
Product loss during isolation and purification.
Impurities in reagents.
How did we determine that atoms are composed of electrons, neutrons, and protons.
By studying the interaction between light and matter.
What did Niels Bohr discover about atoms in 1913?
- Electrons move in orbits around the nucleus.
- Electrons have fixed E (quantised).
- E levels are identified with integers n(n=1 …. infinity)
- Unexcited H atom = electron in the lowest level (n = 1) : ground state.
- Bohr’s model exactly predicts the H atom.
Explain Hund’s rule…
When we get to orbitals of the same energy (e.g. 2p), we need to apply Hund’s rule.
“the most stable arrangement of e- in the same sub-shell has the maximum number of unpaired e- all with the same spin”
Therefore, electrons arrange to have parallel spins in orbitals of the same energy before pairing up.
Briefly explain valence electrons…
For main group elements: Outer shell electrons = valence electrons (VE) = group number
For transition elements: Inner shell electrons can also be valence electrons.
Valence electrons determines the properties of elements and the number of bonds an element will form.
What do Lewis Dot Symbols represent?
The dots in Lewis dot diagrams represent valence electrons.
Usually only used for s and p block elements (periods 1 - 3).
What does isoeletronic mean?
Isoelectronic = equal number of electrons.
Many ions are isoelectronic (main group ions usually adopt the nearest noble gas configuration).
What is the ion electron configuration?
1s2 2s2 2p6 3s2 3p6 ….
Briefly explain Atomic Radii…
Defined as half the distance between 2 identical atoms when bonded to one another.
Estimate of atomic size:
- 1/2 (homonuclear bond length).
Briefly explain what elements on the periodic table do to obtain a full electron shell…
Elements to the left of the periodic table gain electrons to obtain full electron shells.
Noble gases have very stable configurations, meaning they have full electron shells.
Elements to the right of the periodic table loose electrons to obtain full electron shells.
Explain what happens to atoms as they travel down a group or across a period….
Atoms grow when travelling down a group (a larger shell [larger n] is added in each new row).
Atoms shrink when travelling across a period (protons are added to the nucleus. A larger charge pulls all electrons in, therefore shrinking the atom).
When transitioning from Noble Gases to Alkali Metal there is a big jump (a new shell [with larger n] is added).
Briefly explain Ionic radii…
A Cation is smaller than its neutral atom:
- Main block; outer shell completely removed.
- Electron-Electron repulsion is reduced (fewer electrons).
An Anion is larger than its neutral atom:
- More Electron-Electron repulsion (more electrons). Therefore, the shell swells.
Explain the Ionic Radius v. Atomic Radius
Cations are smaller than their parent atom.
Anions are larger than their parent atoms.
What is Ionisation Energy (IE)?
IE is the minimum energy (E) to remove an electron from a gas-phase atom.
IE values are positive (endothermic), therefore must put energy in to remove electron.
The greater the IE, the more difficult to remove an electron.
