CHEM1051 Ch.2 Review

what is our current model of the atom?

compact dense nucleus surrounded by polarized electron cloud

what is electromagnetic radiation?

radiation that can travel through a medium

what are examples of electromagnetic radiation?

radio waves, microwaves, infrared, UV, x-rays, gamma rays

how is electromagnetic radiation characterized?

frequency & wavelength

what is wavelength?

distance from the top of 1 wave to the next

as wavelength changes…

color does too

what is amplitude?

distance from the center line/average of the wave to the max/highest value of a wave

what is amplitude in relation to with color?

bigger amplitude=brighter light

what is frequency?

how many times a wave passes through a point

are wavelength and frequency related?

yes, the longer the wavelength=lower frequency

whats the greek symbol for wavelength?

lambda λ = m

whats the greek symbol for frequency?

ν = # of wavefronts per second

whats the formula for speed of light?

c=λ x v

how does energy of light increase?

as frequency increases and wavelength decreases

what does a short wave length on the electromagnetic spectrum mean?

high frequency & high energy

what does a long wave length on the electromagnetic spectrum mean?

low frequency & low energy

which colors correlate to a short wavelength/high frequency/high energy on the electromagnetic spectrum.

green, blue, indigo, violet

which colors correlate to a long wavelength/low frequency/low energy on the electromagnetic spectrum.

red, orange, yellow, green

what scale does the electromagnetic spectrum have?

log scale 10^1, 10², 10³, etc.

PQ: 2 objects that are 1 m apart(10 degrees m), how far apart of 2 objects that are 10² m apart?

100 m —> 10×10=100

what are wave behaviors of light

diffraction & interference

what is diffraction?

when waves go through a small opening and spreads out

whats interference?

waves that interfere with each other when passing through the same point at the same time

what are 2 types of interference?

constructive & destructive

what is constructive interference?

waves that are in phase; they add up and increase amplitude —> result in more intense electromagnetic wave

what is deconstructive interference?

waves out of phase; waves cancel each out out cause they in opposite positions

what are interference patterns?

bright and dark lines on a screen(evidence that light behaves as waves)

whats the problem with the wave nature of light?(what does it not explain?)

it doesn’t explain the energy of light as it has both wave and particle features.

PQ: which has the longest wavelength? x-rays, visible light, or infrared?

infrared—>lies further on right/red side of electromagnetic radiation spectrum

PQ: which has the highest frequency? x-rays, visible light, or infrared?

x-rays —> lies more on left side of spectrum

PQ: which has the highest energy? x-rays, visible light, or infrared?

x-rays —> x-rays very damaging radiation to body cells without protection

whats our evidence of light as a particle?

black body radiation, UV catastrophe model, & the photoelectric effect

whats black body radiation?

matter emits radiation(energy), and wavelengths & frequency changes as temp changes, which is why night-goggles see various colors emitted from bodies

whats the photoelectric effect?

metal emitting electrons when light falls on it, not expected if light were only a wave

when do electrons get ejected at low, medium or high frequencies?

high frequencies

how do same # electrons get ejected at a faster rate?

increased frequency

how do the same # of electrons get ejected at a slower rate?

decrease frequency

if you increase the intensity of light the # of electrons ejected are…

greater # of electrons get emitted at once but at the same speed(does not affect speed at which electron travel)

what does the threshold for emission of electrons mean?

the minimum amount of energy needed to eject an electron from an atom, ~540 nm

what are small packets of energy called?

photons

do all photons have the same amount of energy in them

no, each photon contains a certain energy

what does the energy of light depend on?

the energy contained within a photon, not on the # of photons

whats the equation for photon’s quantized energy?

E=hv

E=energy

h=planck’s constant: 6.626×10^-34 Js

what determines if electrons get ejected or not & how fast they go?

wavelength

what determines the # of electrons that get ejected?

intensity(amplitude)

what does intensity mean in terms of light being a particle?

how many packets/photons are present?

what does wavelength/frequency mean in terms of light being a particle?

how much energy a photon/packet has

diffraction, interference, refraction, wavelengths, frequency, and amplitude are all explained by what?

wave nature of light

packets/photons, black body radiation, photoelectric effect are all explained by what?

particle nature of light

whats the explanation called for the idea that everything is waves & particles not just light

quantum mechanics

whats the equation used to solve the wave & particles of any object

de Broglie’s equation: λ = h/mv

λ=wavelength

h=plancks constant: 6.626×10^-34

m=mass

v=velocity

where does light come from?

comes from electrons moving between energy levels within an atom/molecule

what determines the color of light

the energy of the photon thats ejected

whats the visible spectrum of light?

very small part of spectrum where white light containing all wavelengths of visible light can be separated by a prism

where dos white light come from?

the sun

whats the atomic emission spectra?

idea that atoms can also emit light

is light emitted from atoms of elements continuous or specific?

atoms can only emit specific wavelengths; different elements emit specific wavelengths based

how does a seperation of color happen?

by a change in frequency of light

what happens when you add white light + prism?

get continuous color spectrum; sun light emits all colors on spectrum

whats the atomic absorption spectrum?

idea that atoms can absorb light

whats the difference between atomic emission and atomic absorption spctrums’s?

emission=specific colors that show up as thin lines on a black spectrum

absorption=specific colors that show up as thin black lines/are blocked on a colorful spectrum

what happens when you pass light on a hot atomic gas+prism?

spectrum showing specific wavelengths(emissions)

what happens when you pass light on a cold gas+prism?

spectrum missing some wavelengths(absorption)

what provides evidence that electrons chamge energy levels?

emission/absorption of electrons

what model is used to demonstrate electron energy changes instead of the Bohr model?

energy level diagrams

what are energy level diagrams

diagram w/ lines to represent different energy levels that electrons can have

what happens to an electron’s energy in excitation

electron jumps from lower energy level to higher one by absorbing a photon, energy of photon=energy difference between the levels

what happens to an electrons energy in de-excitation

electron in higher energy level drops to lower one by emitting a photon

how do electron transition between energy levels?

by emitting or absorbing a photon

what does an energy level diagram w/ arrows pointing down mean?

electrons going down energy level; emission spectrum

what does an energy level diagram with arrows pointing up mean?

electrons moving up energy level, absorption spectrum

what determines wavelength of light being absorbed or emitted?

difference in energy between 2 energy levels

whats the difference between the absorption/emission spectrum and the photoelectric effect?

in the photoelectric effect atoms absorb photons and in the abs/ems spectrum the electron leaves the atom completely to move energy levels

whats the difficulty of wave/particle duality?

cant accurately measure both energy and position of electron; can only know 1 or the other; aka Heisenberg Uncertainty Principle

what’s an atomic orbital?

regions of space where there’s a high probability of finding an electron

how are different orbital described?

based of quantum #’s —> n, l, m, & m sub s

whats the significance of quantum #’s?

every electron in an atom can be described w/ a different set of quantum #’s; no 2 electrons have the same 4 quantum #’s

whats the quantum # “n” ?

is the principle quantum number

can be any positive number

describes whats electron shell looking at

whats the quantum # “l” ?

is the angular momentum quantum #

can have any number 0 to n-1

tells what type of orbital found in a specific shell (spdf)

whats the quantum # “m sub l” ?

is the magnetic quantum #

can have number values from -l(L) to +l(L)

describes specific orbital within that subshell(tells orientation)

what’s the “s” orbital?

only 1 in a set, hold 2 electrons max, the bigger the principal Q# the bigger the orbital & the higher the energy

ex. 1s2, 2s2, 3s2 —> all have 2 electrons

what’s the “p” orbital?

there are 3 orbitals that holds 6 electrons max(2 per orbital)

ex. 2p6, 3p3

what’s the “d” orbital?

there are 5 orbitals that holds 10 max(2 per orbital)

ex. 3d10, 4d5

how many orbitals are in the electron cloud of 1 atom?

all orbitals (all s, p, d, etc.) overlap within electron cloud

how is the periodic table broken up?

broken up into s p d f blocks

whats the general/approximate shape of an atom

spherical

what are core electrons?

low in energy, close to nucleus, very stable, no reaction participation

what are valence electrons?

high in energy, further from nucleus, outside of closed shell, participate in reactions/determine reactivity

how do you find the electronic configuration of an element?

based off the # of electron found in that element, look at atomic #

why’s the periodic table organized in “s p d f” blocks"?

cause its the order that orbitals fill as the atomic # increases

why do elements in columns have similar reactivity?

cause they have the same # of valence electrons

what is atomic radius?

the size of an atom

what happens to the atomic radius as you go down a column?

radius increases cause the # of electrons increase —> more electrons=more volume & bigger orbitals

what happens to the size of an atom when you move across row

atomic radius gets smaller

what does the size of an atom depend on?

1) attractive force between electrons & protons

2) repulsive force between electrons

what’s coulomb’s law?

opposite charges attract, like charges repel

whats the equation to measure FORCE?

f= K x (q1 x q2 / r² )

where q1 & q2 = charges

where r² = distance between charges

what happens to the force as q1 x q2 increases?

it increases

what happens to force as r increases?

force decreases

what’s the atomic radius?

state where forces of attraction between electrons & protons=to forces of repulsion between electrons