Chem 331 - Quiz 1

What is atomic number?

denoted Z, number of protons in an element

What is a neutral atom?

atom with an equal number of protons and electrons

What are orbitals?

mathematical model that tells us the likelihood of finding an electron in a particular location

What is a principal quantum number?

quantum number of an electron that describes its energy level, and electron shell

What happens to an electron when it’s closer to the nucleus?

it’s lower in energy and therefore more strongly held in the electron shell

What is a boundary surface?

region of volume where the probability of finding and electron is high, 90-95%

What is spin and spin quantum number?

number used to describe an electron, can be either +1/2 or -1/2

What is the Pauli exclusion principle?

states that two electrons many occupy the same orbital only when they have opposite or “paired” spins, no orbital can contain more than two electrons

What are nodal surfaces?

regions of a single orbital where the wave function changes sign, the probability of finding an electron in this region zero

What is Hund’s rule?

states when two orbitals are of equal energy, they are half filled by electrons before they are fully filled

What are valence electrons?

electrons in the outermost shell of an atom, make sure to count all orbitals in said shell

What is a valence shell?

group of orbitals responsible for characteristic chemical properties of an atom

What is the octet rule?

states that an atom is most stable, and lower in energy, with a full shell of electrons which is usually 8

What are main group elements?

elements in groups 1A-8A

What are noble gasses/rare gases?

group 8A, have an extremely stable “closed shell” electron configuration, have a complete octet, are very unreactive

What are compounds?

2+ combined atoms, have properties different from atoms contained

What is a chemical bond?

attractive force between atoms in. a compound

What is an ionic bond?

attraction between oppositely charged ions

What is ionization energy?

amount of energy required to remove an electron from some species/dislodge an electron

What is an endothermic process?

process that absorbs energy

What is an exothermic process?

process that releases energy

What is electron affinity?

energy change for addition of adding an electron to an atom

What are electrostatic/Coulombic forces?

forces between charged particles, constitute ionic bond when attractive

What is bond dissociation enthalpy?

energy required to break a bond while each atom retains one of the electrons in said bond

What are unshared/lone pairs?

electrons pairs not involved in bonding

What is a polarized electron distribution?

when an atom has a greater tendency to attract electrons in an electron distribution, in bonds this is a polar covalent bond

What is electronegativity?

tendency of an atom to attract electrons in a covalent bond

What is an electronegative element?

element that attracts electrons

What is an electropositive element?

element that donates electrons

What is an electrostatic potential map?

way of illustrating electron polarization graphically, blue denotes more positive charge while red indicates more negative charge

What is the periodic trend for electronegativity?

increases across a period and decreases across groups, fluorine is the most electronegative element

What is a dipole moment?

product of attractive force between 2 opposite charges and the distance between them

What is formal charge?

difference between number of valence electrons and number of valence electrons in a bonded states

What is the formula for valence electrons?

#valence electrons - # bonds - # dots

What is connectivity of a molecule?

order in which a molecule’s atoms are connected

What are isomers?

different compounds that have the same molecular formula

What are constitutional isomers?

isomers that differ in connectivity

What are stereoisomers?

isomers that differ in arrangement of atoms in space, sometimes called structural isomers

What is a condensed formula?

formula that omits bonds altogether, ex. CH₄

What are bond-line formulas?

formulas in which labels for individual carbons are omitted and hydrogens attached only shown for clarity

What are heteroatoms?

atoms other than carbon or hydrogen are shown explicitly as are hydrogens attached to them

What are curved arrows?

arrows that denotes the movement and direction of movement of an electron pair, electrons move from tail end to the head end of an arrow

What is a single bonded arrow?

arrow that denotes the movement of one electron

What is resonance?

when 2+ lewis formulas differ only in distribution of electrons, no single formula is sufficient to describe the true electron distribution, the true structure is a resonance hybrid of the lewis formulas called contributing structures

What are contributing structures?

various resonance structures that can be written for a molecule

What are localized electrons?

electrons that associate with a single atom

What are delocalized electrons?

electrons associated with more than one atom

What is the caveat to lewis formulas?

they show localized electrons but electrons can be delocalized

If there are two electron domains with no lone pairs, what is the electron domain geometry, molecular geometry, and angle?

EDG: linear

MG: linear

angle: 180

If there are three electron domains with no lone pairs, what is the electron domain geometry, molecular geometry, and angle?

EDG: trigonal planar

MG: trigonal planar

angle: 120

If there are three electron domains with one lone pair, what is the electron domain geometry, molecular geometry, and angle?

EDG: trigonal planar

MG: bent

angle: <120

If there are four electron domains with no pairs, what is the electron domain geometry, molecular geometry, and angle?

EDG: tetrahedral

MG: tetrahedral

angle: 109.5

If there are four electron domains with one lone pair, what is the electron domain geometry, molecular geometry, and angle?

EDG: tetrahedral

MG: trigonal pyramidal

angle: <109

If there are four electron domains with two lone pairs, what is the electron domain geometry, molecular geometry, and angle?

EDG: tetrahedral

MG: bent

angle: <109

If there are five electron domains with no pairs, what is the electron domain geometry, molecular geometry, and angle?

EDG: trigonal bipyramidal

MG: trigonal bipyramidal

If there are five electron domains with one lone pair, what is the electron domain geometry, molecular geometry, and angle?

EDG: trigonal bipyramidal

MG: seesaw

If there are five electron domains with two lone pairs, what is the electron domain geometry, molecular geometry, and angle?

EDG: trigonal bipyramidal

MG: t-shaped

If there are five electron domains with three lone pairs, what is the electron domain geometry, molecular geometry, and angle?

EDG: trigonal bipyramidal

MG: linear

If there are six electron domains with no pairs, what is the electron domain geometry, molecular geometry, and angle?

EDG: octahedral

MG: octahedral

If there are six electron domains with one lone pair, what is the electron domain geometry, molecular geometry, and angle?

EDG: octahedral

MG: square pyramidal

If there are six electron domains with two lone pairs, what is the electron domain geometry, molecular geometry, and angle?

EDG: octahedral

MG: square planar

What is the formal charge pattern of carbon?

can form four bonds, one less is negative, removal of lone pair is positive (carbocation)

What is the formal charge pattern of nitrogen?

can form three bonds, one less is negative, one more is positive

What is the formal charge pattern of oxygen?

can form two bonds, one less is negative, one more is positive

What is the formal charge pattern of fluorine?

can form one bond, one less is negative

What is the formal charge pattern of chlorine?

can form one bond, one less is negative, one more is positive

What is the formal charge pattern of hydrogen?

can form one bond, an extra lone electron is negative, removal of an electron is positive (proton)

What does a solid wedge bond style indicate?

bond projects toward you

What does a hashed wedge bond style indicate?

bond points away from you

What does a simple line bond style indicate?

bond lies in plane of paper

What is the valence shell electron-pair repulsion model (VSEPR)?

idea that electron pairs, bonded or unshared, will be as far away as possible from other electron pairs

What takes up more space, an unshared pair or a bonded pair?

bonded pair

Rank repulsive forces of unshared versus bonded electron pairs from least repulsive to most repulsive

least

• bonded versus bonded pair

• unshared versus bonded pair

• unshared versus unshared pair

How does symmetry affect polarity and dipole moments?

if a molecule is symmetrical with all the same outside atoms, then it is a non polar molecule with a net dipole of zero

What is molecular symmetry?

a central atom is surrounded symmetrically by the same type of atom, causes symmetric charge distribution

What do curved arrows show?

ALWAYS show electron flow