7.3 electron affinity and electronegativity Flashcards
(16 cards)
Electron Affinity is the exact opposite of ionization energy
* ionization energy = the E to remove an electron
* This is now atoms gaining an electron
* You dont have to push electrons onto an atom, thats where they want to be. Doesnt take E. These are exothermic rxns, not endothermic (meaning the system gives off energy and the surroundings gain E w/ this rxn)
Cl has the most electron affinity of all the elements. It will release the most energy when an electron is bound to it. If you give Cl an electron it will shower you with energy (its an exothermic rxn, meaning the environment gains E and the system loses it, unlike the ionization rxns)
However, there are some exceptions to this rule
Ar, just the the R of Cl has a filled octet and does not want any more electrons. So it will actaully take E to bind an electron to it (meaning were adding energy to the system and taking it away from the environment = endothermic rxn)
Exceptions
* this is where its actually an endothermic rxn, meaning were needing to add energy from the enevironment to the system to bind electrons to the atom (these atoms don’t really want electrons, unlike most of them)
All the nobel gases don’t want extra electrons. Have to add E to bind electrons here. This makes since because they have a full valence shell and don’t want anything else
All the elements in the Sp^2 orbital don’t want electrons because they already have a full subshell and don’t want anymore (Be, Mg, Ca etc…)
The half filled P subshells also follow this trend of not wanting electrons. Remember, they’re in a fairly stable state when they’re half filled, so don’t want anymore electrons to mess this up. It will cost E to bind electrons here.
These exceptions are in the exact same place as they were w/ ionization E. + the nobel gases
For electron affinity it increases going to the right (meaning the elements to the right give off more E when binding w/ an electron, aka they want it more)
* however, theres no vertical trend, just L –> R trend
increases = bigger exothermic rxn, or the E gets more negative
* increasing for electron affinity = getting more negative
Period 17 elements typically have the most electron affinity (meaning they really want an electron to fill their valence shell)
* so it gets more negative as you approach this group
its negative because the system loses energy when the electron is bound
* however, when a system is more attracted to the electron it will lose more energy
* So Cl has the most electronegativity (really wants an electron and gives up the most eneergy when that electron is bound to it
The trend we just learend only applies to the first electron affinity.
Sucessive electron affinity adding 2 electrons +
nobody wants to gain more than 1 electron. Think about oxygen the atom. Its neutral, however once it gains its first electron it turn into an anion (O-). Now its negatively charged and doesnt want electrons, a negative and a negative repell eachother.
So sucessive electron affininities are not negative exothermic reactions (don’t give the environment energy), they’re actually endothermic rxns, meaning the cost the environment energy and give the system energy. It takes energy to put them on the electron
* meaning the system is gaining energy (which is why its positive) and the environment is losing energy
* Remember, its always from the systems persepective
electron affinity is again specifically for the gas state
Electronegativity
Fluorine is the most electronegative atom
Turns out the electrons arent shared evenly between atoms when they bond. The more electronegative atom pulls harder on the electrons
The red below is indicating a partial charge on the covalently bonded atoms.
* since fluorine is more electornegative it holds the bound electrons (in the bond between carbon in F) closer to it the majority of the time. This gives it a partal negative charge, while conversly carbon recieves a partal possitive charge.
The bigger the difference in electronegativity between the two bound atoms the bigger the partial charge - this is a polar bond
* note the partial charge is less than 1. If electrons were fully pulled off an no longer bonding them thats when we would consider full charges
When the difference in electronegativity gets large enough we create an ionic bond (where an electron is pulled off entirely)
* This is a metal and a non-metal
Electronegativity trends:
* increases as you go to fluorine
noble gases left out because they dont really form bonds
Oxygen is more electronegative than Cl. Meaning R –> L matters more than down –> up
So electron affinity means its grabbing an electron
most negtaive means that the most energy is lost from the system when the electron is pulled in (exothermic rxns = negative #’s)
F
remember the trend for affinity is from L –> R = increased E released = bigger affinity (more energy is released when they want the electron more)
* note the exceptions below
cl
so now were talking about electronegativity, not affinity
F is the answer
Remember, the trend for this is L –> R, and down –> up
most polar bond means the biggest devations in electronegativity between the 2 atoms
So the P’s are all the same, with a lower electronegativity
* now we just have to find the other one w/ the large electronegativity
* Remember, electronegativity increases from down –> up and from L –>R
P-F
Metallic - pure elemental metal
* Good conductors of heat and electricity
* valence electrons are loosely held throughout a metal –> allow the flow of electrons (electricity) through a metal
* Luster - meaning they are shiny
* malleable - can pound them into different shapes
* Ductile - can be drawn into wires
Non metals - insulators - not good conductors of electricity
Semi metals (metloids) - are semi condcutors
Ionic substance - metal + nonmetal
* high melting point
* High boiling point
* When you are boiling / melting you are breakin if not all of the ionic bonds, and breaking bonds takes a lot of E (heat in this case)
* Brittle - think about having a big salt block, that would shatter it into a million peices. Well if you do that w/ iron the same tihng is going to happen. Ionic compoudns are brittle and will shatter into a million peices
* The reason they are brittle (shown below) is because they’re in rows of +/- where the +’s are always surrounded by -‘s. When you hit it w/ something its going to shift the row’s over, making the +’s surrounded by other +’s and thereby making them repulsed by eachother, and break into a million peices
* Latice energy is proportional to the charges and inversly proportional to the distance between the charges (r) sqaured. The more attracted the cations and anions in the ionic substance, the bigger the attraction between them and the closer they are (r) the stronger the force between them. So basically that measure of how attracted the ions are to eachother in the ionic compound = lattice E
Molecular compounds:
* Dont form big crystals the way ionic compounds do, they form discrete molecules
* low melting point (arent held together as strongly)
* Low boiling point (arent held together as strongly)
Network covalent solid:
* Few and far between
* all non metals, but form a crystal lattice structure, and though its moelcularly bonded (not singlular like the normal molecularly bonded molecules)
* diamond, quartz
* however, this is the rare to find these
* its crystals held together by covalent bonds
* high melting point - think trying to melt a diamond
* high boiling point
group 1 metals have a very low ionization E (meaning its very easy to take that first electron off)
* they’re going to combine w/ non metals very readily to form ionic compounds
* Also are very reactive w/ H2O
Alkali means basic
* the alkali metals are called alkali because when they’re combined w/ H2O they form a hydroxide salt (NaOH) which is one of your strong bases
* they get more reactive w/ H2O as you go down the group (getting lower and lower ionization energies as you go down because theres more shielding electrons)
Alkaline earth metals (also means basic)
* Note quite as reactive w/ H2O, but still reactive.
* Ionization E’s not as low as alkali metals
noble gases are chemically inert - they dont react much
* due to the filled octet
Halogens: have high electron affinities
* most negative electron affininities
* combine w/ metals very readily to form ionic compounds
Chalkogens (Oxygens group)
* Sulfides are very insoluble
* most stable form of oxygen has O2, however it also exists as O3 (ozone). When an element has more than 1 elemental form we use the word allotropes
* O2 and O3 are allotropes
* Metal oxides = Na2O - metal oxides tend to be basic. Na2O + H2O —> 2NaOH (forms a base)
* Nonmetal Oxide = CO2 - tend to be acidic: CO2 + H2O –> H2CO3
