Chem Test 2 Unit 1

daltons experiment

dalton described the atom as a small hard sphere. All elements were made of many spheres. Since atoms of each element are diff from one another, the spheres for each element were slightly diff

daltons 5 part atomic theory

1. all elements are made of atoms
2. atoms of an element are identical
3. atoms of diff elements are diff
4. atoms combine in simple whole number ratios to make compounds
5. atoms may rearrange in chemical rxns, but are not changed in the reaction.

today we still agree with 1,3,4,5

we dont agree with 2 bc not all elements of the same atom are identical bc of isotopes

thompshons expirements

part 1: thompshon used a hollow glass tube w metal plates on either end. He removed the air from the tube and connected the tube to an electricity source. He found that "rays" travelled acroos the tube from the cathode to the anode.

part 2: thomson exposed the ray to a magnet and found that the ray bent toward the pos. end of a magnet and away from the negative end.

part 3: thomson used an electric field to measure the mass to charge ratio of the ray. He found this ratio to be almost 2000 times larger than the mass to charge ratio for a charged hydrogen atom. So,,, either the ray particles had a huge charge or very small mass

what did thomson discover

the electron.

The cathode ray evidences this bc it is negatively charged like an electron bc it is attracted to the positve end of the magnet and repels the negative end of the magnet.

thomson's atomic model

he modified thomson's model to add a pos. charged "base" material that had small negatively charged particles removeable but imbeedded. Called it plum pudding model.

Accurate bc electrons are seperable part of atom

inaccurate bc the idea of the positive plum pudding fill

Rutherford's experiments

used alpha particles to test Thomson's model. Alpha particles are helium nucleus emitted during radioactive decay.

Experiment used sheet of gold only 2-3 atoms thick. Alpha particles were released from a lead box and 99.999% of the particles passed through the gold foil. A very small number were deflected.

Discovery of radioactivity and ability to seperate radioactive emissions was necessay for experiment.

Rutherford's discovery

He found the nucleus that is positively charged, as evidenced by the deflection of some alpha particles, and some directly back due to repelling same charges

Rutherford's model for an atom

held onto Thomson's idea of pos. and neg. parts. He modified Thomsons to specifiy that the pos part of the atom was contained in a small dense nucleus, and that the electorns orbited the nucleus like planets around the sun.

True that the pos. part of the artom is a small and dense area at the center of the atom

False that electrons orbit like planets

Bohr's experiment

realized that when a sample of hydrogen gas was exposed to electric current it released energy as light. specific wavelengths sen corresponding to different lights for each distinct element. disproved Bohr's orbit model bc in Bohr's the orbit would cause a continuous rainbow of colors not distinct lines.

Bohr's model

held Ruth model with nucleus pos charged and electrons orbiting, just not like planets. He specified in his model that electron orbits were a set distance from the nucleus, and that each orbit contained a specific amount of energy.

we still argee with electron orbits corresponding to specific amounts of energy

we dont agree with the orbits being a fixed distance from nucleus

what did Bohr discover

that electrons travel in orbits of discrete energy as evidenced by the line emission spectra for light in which certain wavelengths emitted

current model: quantam mechanical model of the atom

principal quantam number (n) describes the energy of an electron.

princ quantam number = energy level.

did experiments with the Heisenberg Uncertainty Principle and found thast we only know where to prob find electrons = probability orbitals

Rutherford to current

Rutherford's cloud became the probability density which gave us orbital shapes

cathode ray tube

two plates connected to voltage

cathode shoots rays that pass through anode and travels to other end of tube and produces bright flourescent light

electric field is added to the tube. cathode ray is attracted to the positive plage and repels the neg plate and bends

in magnetic field rays repel neg end and are attracted to positive

cathode ray tube charge to mass ratio

set up electric fields so that the electrostatic reflection was the same as the same as the magnetic deflection

came up with equation for finding charge to mass ratio

(E times theta subscript e)/(B^2 times L)

E=applied electric field
theta=angle of delfection

B=applied magnetic field
L=distance traveled by cathode rays

found the charge to mass ratio of an elctron = -1.76 times 10^8 coulombs per gram

Milikans oil drop experiment

found charge of electron

sprayed mist of oil into upper chamber, some fell through hole in floor
used terminal velocity of falling to find mass of the oil drop
used an x-ray to ionize oil droplets by adding on to them a neg charge
oil drops can be suspended between two plates if the voltage of positive and negative is balanced right
if too neg then falls to negative
if too pos than rises to positve

when suspended, the weight of the droplet equals the force keeping it up from the magnetic field

found the charge of an electron to be -1.60 times 10^-19 coulombs

used charge paried with charge to mass ratio to find mass

photoelectric effect

observation that if a certain metal plate is hit with light, an electron is ejected

ability for electron ejection dependent on frequency

light made of photons= particles of light, electron is ejected when struck by singular proton with sufficient energy

low frequency low energy

energy of photon= plancks constant times frequency

proves that light has particle nature bc it is made up of photons which r particles of light

emmision/absorption spectra

show the energy emmited/absorbed when electrons change energy levels. Rydberg equation calculates the wavelength of energt emitted or absorbed by a hydrogen electron transitioning from one level to a new level.

rydberg equation

1/wavelength=1.097times10^7m^-1(1/n^2 final - 1/n^2 initial)

equation relating emission lines to the energy level of the electron in hydrogen

Energy of certain level= -2.178 times 10^-18 Joules (atomic number squared/energy level squared)

electromagnetic spectrum

order from most frequency to least frequency and least wavelength to most wavelength:

gamma rays
x rays
UV
visible light (VIBGYOR)
IR
microwaves
radiowaves
long radio waves

longer wavelength

=less energy

speed of light

C
2.99*10^8 m/s

wavelength

lambdha
the distance between successive crests of a wave, especially points in a sound wave or electromagnetic wave.
meters

frequency

nu
the number of waves that pass a fixed point in unit time
1/s=s^-1=Hz

Energy

E
Joules

speed of light

=frequency times wavelength

plancks constant

6.626 times 10^-24 Joules times seconds
h

Energy

e=hv

e=(h*c)/wavelength

determining radioactivity

over 82 protons is radioactive always

proton deficent

more neutrons than protons undergoes beta decay

14C6 to 14N7 + 0e-1

goes from neutron to proton loses a Beta particle=0e-1
same mass but different element (+1)

proton rich

more protons than neutrons

a) electron capture
turns a proton into a neutron
1P1+0e-1 to 1n0

add an electron so same mass but different element (-1)

b) positron emission
turns a proton into a neutron by emitting a positively charged positron
10C6 to 10B5+0e1

same mass but one less proton

alpha decay

way to reduce protons by shedding alpha particle

210Po84 to 206Pb82 + 4He2

Loses 4 mass and 2 protons

mass spectrometer

enter atoms, ionize them, shoot them through accelerator, use charges to deflect them, detetct them

ionization

electrons are knocked off sample particles to mostly form +1 ions

acceleration

ions move through a series pf changed plated to form a narrow beam of high speed particles with eqaul kinetic energy

deflection

Ions are attracted to the negative side of an electromagnetic field causinf separation of the mixture based on mass and charge

detection

ions collide with a metal plate. Electrons are transferred from the metal to the ion, producing a current and thus a signal to a computer

what causes the sample mixture to become seperated

the mass of the ion

lighter particles seperate mkre

relationshio between mass to charge ratio and deflection

smaller mass to charge ratio greater deflection

percent natural abundance vs relative abundance

percent abundance gives the abundance of isotopes whereas relative abundance gives the abundance of chemical elements.

if something is diatomic but has more than one natural isotope need to account for all possible combinations

parent peak

The most intense (tallest) peak in a mass spectrum, due to the ion with the greatest relative abundance

valence electrons

in outermost shell

outer core electrons

not in outershell but comes after core elctrons

core electrons

occupy lowest energy levels

p block orbital diagram labels

number of energy shell px py pz

d block orbital diagram labels

dxy dy^2 dx^2 dz^2 dx^2-y^2

reading PES

closer to nucleus more energy to ionize

height is number of electrons in shell

coulombic attractions

Coulombic attraction is the force of attraction between positive and negative charges.

Determined by distance and number of protons

more protons more charge so more attractive force so therefore smaller atomic radii as more condesnsed

more distsncde (more energy levels) less attractive force bc greater distance between proton and electrons

smaller atomic radii greater coulombic force

periodic trends

row = period
column =fam or group

down a fam: increase in atomic radii bc there are energy levels being added so therefore the distance from valence electrons to the nucleus is increasing. Although gaining protons, the change in distance is more significant to coloumbic forces

across a period: decrease in atomic radii bc all in the same energy level there no increase in distance, however increase in protons therefore increase in strength of coloumbic forces

connection between coloumbic forces and ionization energy

ionization energy higher for higher coloumbic forces

coloumbic forces and electron affinity

electron affinity = measure of affinity for electrons
neg electron affinity is exothermic meaning makes energy when gettingelectron
pos electron affinity is endothermic means takes energy to get electron
halogens have most neg electron affinity bc one away from full octet
noble gasses and elements with full subshells have most electronegativity bc already full and cant take more

electronegativity

a measure of an atoms ability to share electrons
directly proportional with coloumbic forces: increase coloumbic force increase electronegativity bc more force from nucleus to pull in electrons

alpha particles

He2+ emitted by radioactive nucleus
positevly charged
least ability to pass through things

beta particles

a fast-moving electron emitted by radioactive decay of substances.
negatively charged
2nd most ability to pass through things

gamma rays

penetrating electromagnetic radiation of a kind arising from the radioactive decay of atomic nuclei
neutral
most ability to pass through things

band of stability (n to p ratio)

smaller atoms = 1:1
bigger = 1.5:1