general chemistry - unit 2

test 2

what are the periodic trends?

* atomic radius
* ionic radius
* ionization energy
* electron affinity

in what directions across the periodic table does the radius of an atom increase?

left and down

are cations larger or smaller than neutral atoms?

smaller

are anions larger or smaller than neutral atoms?

larger

why does the ion size increase down the column?

higher valence shell, larger

what does isoelectronic mean?

same electron configuration (ex: N3-, O2-, F-, Ne: 1s22s22p6)

for atoms or ions that are isoelectronic, what determines the size?

number of protons

what is the relationship between the nuclear charge and radius of isoelectronic atoms?

greater nuclear charge, smaller radius

what is ionization energy?

minimum amount of energy to remove a loosely bound electron from a gaseous atom in its ground state

is ionization energy always exothermic or endothermic?

endothermic

are core electrons or valence electrons easier to remove?

valence

are ie (ionization energy) values always negative or always positive?

positive

what is the relationship between atomic radius and ionization energy?

atomic radius increases, ionization energy decreases

in what directions across the periodic table does the first ionization energy increase?

right and up

what causes deviations in the ionization energy trend?

* penetration and shielding; an *s* electron is harder to remove from an atom than a *p* electron in the same shell
* breaking a full sublevel costs more energy than ionizing a full sublevel
* removing a single paired electron (not full subshell) eliminates electron-electron repulsion, and therefore is energetically favourable

for which columns does the first ionization energy not increase from left to right?

2A to 3A and 5A to 6A

what is the strength of attraction of an electron related to?

distance the valence electrons are from the nucleus, effective nuclear charge

which is more difficult: removing an electron from a cation (more positive charge) or from a neutral atom (more negative charge)?

removing an electron from a cation is more difficult because of greater electrostatic attraction to the cation

what does the fact that cations are harder to remove an electron from than neutral atoms tell us?

successive ionization energies for an element always increase (X2+ > X+ > X > X-)

what explains the large increase in successive ionization energies for an element?

the removal of core electrons, which takes much more energy

what is electron affinity?

change in energy released when a neutral atom gains an electron (forming an anion)

is electron affinity exothermic or endothermic?

exothermic

what is the correlation between energy released and electron affinity?

more energy released, larger electron affinity

what is the name given to the element with the highest electron affinity in any period?

halogen

for alkali metals, in what direction does electron affinity increase?

up

generally, in what direction across the period does electron affinity increase?

right

which groups typically have lower electron affinities and why?

5A - an extra electron must pair

2A and 8A - added electron goes into higher sublevel

what is the other name for lewis structures?

electron dot diagrams

when do chemical bonds occur?

when the potential energy of the bonded atoms is less than the potential energy of the separate atoms

what interactions need to be considered when calculating potential energy between charged particles?

* nucleus-nucleus
* electron-electron
* nucleus-electron

what does a metal become if it loses an electron?

cation (becomes more positive)

what does a nonmetal become if it gains an electron?

anion (becomes more negative)

what makes it relatively easy for metals to lose an electron?

low ionization energy

what makes it advantageous for nonmetals to gain an electron?

high electron affinity

why do nonmetals bond together covalently (sharing electrons)?

better in terms of potential energy, more difficult to remove electrons

what positioning of the shared electron minimizes the potential energy, therefore maximizing the stability?

electron directly between the nuclei

how do metals form cations?

by losing enough electrons to get the same electron configuration as the previous noble gas

how do nonmetals form anions?

by gaining enough electrons to get the same electron configuration as the next noble gas

what is the octet rule?

atoms will bond to form a full outer valence shell of eight electrons

what are the two main exceptions from the octet rule?

* H, Li, Be, B attain an electron configuration like He
* elements in period 3 or below use empty valence *d* orbitals

how is the lewis structure of a cation written?

without valence electrons

how is the lewis structure of a cation written?

with eight valence electrons, often in \[\] to denote completion

what does the lewis theory predict for ionic bonding?

* number of electrons lost or gained (octet rule)
* formulas of ionic compounds
* relative strengths of ionic bonds (coulomb’s law)

what is a crystal lattice?

structure that maximizes attractions between cations and anions, maximizing stability

why do no ionic molecules exist?

electrostatic attraction is nondirectional, no direct pair of anion and cation

what is lattice energy?

energy released when the solid crystal forms (crystal lattice)

is lattice energy exothermic or endothermic?

exothermic

what is the relationship between lattice energy and size or charges?

larger lattice energy, larger charge

what is the relationship between lattice energy and distance between ions?

larger lattice energy, smaller distance between ions

what does the born-haber cycle represent?

hypothetical series of reactions that represent the formation of an ionic compound

what does the lewis theory predict about the hardness of ionic solids? is this accurate?

ionic solids are hard. yes, this is accurate

what does the lewis theory predict about the brittleness of ionic crystals? is this accurate?

ionic solids are brittle. yes, this is accurate

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what does the lewis theory predict about the electronic conductivity of ionic solids? is this accurate?

ionic solids do not conduct electricity. yes, this is accurate

what does the lewis theory predict about the electronic conductivity of liquid ionic compounds and ionic compounds dissolved in water? is this accurate?

ionic compounds conduct electricity in the liquid or aqueous state. yes, this is accurate

why do nonmetal atoms bond covalently?

better in terms of potential energy, nonmetal atoms have high ionization energies, making it difficult to remove electrons from them

what are the electrons that are shared by atoms in covalent bonds called?

bonding pairs

what are the electrons that are not shared by atoms in covalent bonds called?

lone pairs, nonbonding pairs

how many electrons are shared in a single covalent bond?

two electrons

how many electrons are shared in a double covalent bond?

four electrons

how many electrons are shared in a triple covalent bond?

six electrons

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which elements are diatomic molecular elements?

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hydrogen and halogens

generally, how many bonds does oxygen form in its molecular compounds?

two bonds

which atom is central in lewis structures?

least electronegative

what does the lewis theory predict about the arrangement of atoms in covalently bonded compounds? is this accurate?

compounds are made of individual molecules. yes, this is accurate

what does the lewis theory predict about the melting and boiling points of molecular compounds? is this accurate?

molecular compounds have low melting and boiling points. yes, this is accurate

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why do molecular compounds have low melting and boiling points?

involves breaking the attractions between molecules, but not the bonds between the atoms

what does the lewis theory predict about the hardness and brittleness of molecular compounds? is this accurate?

hardness and brittleness vary. yes, this is accurate

what does the lewis theory predict about the electronic conductivity of molecular solids and liquids? is this accurate?

neither molecular solids nor liquids conduct electricity. yes, this is accurate

what is the only state in which a molecular compound can conduct electricity?

molecular acids ionize when dissolved in water, and therefore conduct electricity

true or false: in terms of bond strength, triple bonds > double bonds > single bonds

true

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true or false: in terms of bond length, triple bonds > double bonds > single bonds

false

what causes bond polarity?

unequal sharing of electrons

according to the vsepr theory, what shape is a structure in which the central atom has two electron groups?

linear (all angles 180)

according to the vsepr theory, what shape is a structure in which the central atom has three electron groups?

trigonal planar (all angles 120)

according to the vsepr theory, what shape is a structure in which the central atom has four electron groups?

tetrahedral (all angles 109.5)

according to the vsepr theory, what shape is a structure in which the central atom has five electron groups?

trigonal bipyramidal (angles between equatorial positions 120, angles between axial and equatorial positions 90)

according to the vsepr theory, what shape is a structure in which the central atom has six electron groups?

octahedral (all angles 90)

according to the vsepr theory, what shape is a structure in which the central atom has three electron groups and one lone pair?

trigonal planar bent (all angles less than 120)

according to the vsepr theory, what shape is a structure in which the central atom has four electron groups and one lone pair?

pyramidal (all angles less than 109.5)

according to the vsepr theory, what shape is a structure in which the central atom has four electron groups and two lone pairs?

tetrahedral bent (all angles less than 109.5)

according to the vsepr theory, what shape is a structure in which the central atom has five electron groups and one lone pair?

seesaw (angles between equatorial positions less than 120, angles between axial and equatorial positions less than 90)

according to the vsepr theory, what shape is a structure in which the central atom has five electron groups and two lone pairs?

t shaped (angles between between equatorial positions 120, angles between axial and equatorial 90)

according to the vsepr theory, what shape is a structure in which the central atom has five electron groups and three lone pairs?

linear (all angles 180)

according to the vsepr theory, what shape is a structure in which the central atom has six electron groups and one lone pair?

square pyramid (all angles less than 90)

according to the vsepr theory, what shape is a structure in which the central atom has six electron groups and two lone pairs?

square planar (all angles 90)

how do you calculate bond order?

\# of electron pairs / # of bonded atom pairs

what is the order of values on a born-haber cycle?

1. sublimation / vaporization energy
2. ionization energy
3. bond energy
4. electron affinity
5. lattice energy