Answers to the Questions relating to Atoms, Orbitals and Electron Configurations:

Atoms:

1.  How many electrons are there in N^3-?
            N has 7 electrons so N^3- has 7+3 = 10, 8 valence and 2 core

2.  What is the atomic mass unit for an atom of bromine?
            79.904 amu, this is a weighted average of the isotopic masses for ⁷⁹Br and ⁸¹Br.

Orbtials:

1.  What are the quantum numbers that describe a 3p orbital?
            First determine what quantum numbers are indicated by the name 3p.

            Any of the following 'sets' of quantum numbers will be valid:

 

n	l	ml
3	1	1
3	1	0
3	1	-1

2.  How many occupied valence orbitals are there in Cl and I?
 

First consider their electron configurations (core, valence)
 

Both have a total of four, occupied, valence orbitals, one s orbital and three p orbitals.

3.  What are the quantum numbers for an electron in a 3s orbital?

First determine what quantum numbers are indicated by the name 3s.

Then note that you want the quantum numbers for an electron so m_s must also be considered!
either of the following 'sets' of quantum numbers is valid.

 

n	l	ml	ms
3	0	1	-1/2
3	0	-1	+1/2

Electron Configurations:

Use the information given in the box below when answering the next three questions:
 

1.  Which of the electron configurations above best describes the ground state electron configuration of Cl^-? (a)
2.  Which of the electron configurations above is possible for the ground state of P?  (e)
3.  Which of the electron configurations above describes an excited state of Mg⁺? (c)

4.  Is the following electron configuration consistent with Hund's rule of maximum multiplicity?

5.  Is the following electron configuration consistent with Pauli's exclusion principle?

6.  What is the orbital energy diagram that best describes the core electron configuration of Si ?

Did you draw the core or did you draw the valence electron configuration by mistake ?

7.  What is the orbital energy diagram that best describes the valence electron configuration of O ?

Did you draw the valence or did you draw the core electron configuration by mistake ?

 

Answers to Questions relating to Bonds and Bond Polarity:

1.  What types of bond exists between the atoms in a molecule of methyllithium?

The formula for this compound can be written as [Li⁺][CH₃^-], the methyl anion is formed by covalent bonding between carbon and hydrogen.  Though there is no significant bond polarity to a C-H bond there is a molecular polarity to the anion because of the negative charge placed on carbon.  The attraction of the Li⁺ cation to CH₃^- is ionic.

2.  What types of bonds exist between the atoms in a molecule of sodium sulfate?

The formula for this compound can be written as [Na⁺]₂[SO₄^2-], the sulfate anion is formed by covalent bonding between sulfur and oxygen.  Since there is a bond polarity to a S-O bond these are polar covalent bonds.  The attraction of the Na⁺ cations to SO₄^2- is ionic.

3.  What types of bond exist between the atoms in a molecule of chlorine gas?

 Covalent non-polar bonds exist between the atoms in a molecule of Cl₂.

 

Answers to Questions relating to Lewis diagrams and Resonance:

Lewis Diagrams:

1.  Give a Lewis diagram for the following reagents:  HNO₃, H₂SO₄, and sodium azide.

2.  Give the Lewis diagrams for the following molecules:

Resonance:

3.  A carbonyl compound, for which resonance is important is the enolate ion.   Consider [CH₃CH-C(O)-CH₃]^- (but-3-ene-2-olate), see if you can find the two major resonance structures for this molecule.

4.  Aromatic ring systems often display resonance, show what the electron delocalization in a compound like p-nitroaniline would be like.

 

Answers to Questions on the Shapes of Molecules:
 

1.  Give a drawing that clearly indicates the orientation of the atoms in 3-butenaldehyde, CH₂CHCH₂CHO, in 3D space.   On this diagram indicate the electronic geometry about all non-hydrogen atoms.

2.  Using a diagram, indicate the direction of molecular polarity for 3-butenaldehyde.

Hybridization:

1.  What is the hybridization around all atoms other than hydrogen in ethene, CH₂CH₂, and ethyne, CHCH?

The carbons in ethene are sp² hybridized.

The quickest way of determining this is to count the groups around carbon, two hydrogens and one CH₂, and then this will be equvalent to the number of orbitals that must hybridize (3).  The name of the hybrids will be taken from the orbitals that must mix, from lowest to highest in energy that must be one s orbital and two p orbitals.

Similarly for ethyne the carbon atoms are sp hybridised.

2.  Draw the s and p bonding interactions for ethene, CH₂CH₂, and ethyne, CHCH.