exam 1 Flashcards
chemistry is the study of
the composition, properties, and interactions of matter
alchemy
pseudoscience involved with transforming cheap metals into gold
- contribution: methods to prepare mineral acids (HCl, HBr, etc.)
Phlogiston Theory & Antoine Lavoisier
- outdated explanation for combustion
- “phlogiston” spirit present in fire and when it burned, the spirit burned out = explained why fire eventually died out
Antoine Lavoisier: explained true nature of combustion, carefully weighed reactants and products, suggesting that matter is neither created nor destroyed
the scientific method involves 3 steps:
- making observations (collecting data)
- suggesting explanations (hypothesis)
- conducting experiments (testing experiments)
theories vs. laws
laws: describe or predict facets of the natural world
- a law summarizes WHAT happens
theories: well-tested hypotheses that explain a phenomenon
- theory attempts to explain WHY something happens
3 domains of chemistry
- macroscopic: things you can sense around you
- microscopic: what’s happening when you zoom in (water molecules)
- symbolic: use of symbols, formulas, and equations to represent chemical concepts
- H2O for water
matter definition & 3 states
matter: anything that has mass and occupies space
- solid
- liquid
- gas
mass vs. weight
mass: amount of matter present in an object
weight: refers to the force that gravity exerts on an object
pure substances
- have a constant composition
elements & compounds
elements: cannot be broken down into simpler substances by any means (iron, silver, gold, etc.)
compounds: can be broken into elements via chemical changes (carbon dioxide, water, etc.)
compounds are pure substances bc only one type of substance in this mixture
mixtures + 2 types of mixtures
mixtures: composed of 2 or more types of matter that can be separated by physical changes
- homogeneous: indistinguishable components (solutions) uniform composition
- heterogeneous: visibly distinguishable components
atoms vs molecules
atoms: smallest particle of an element which have properties of that element
molecules: consist of two or more atoms joined by forces called chemical bonds
physical vs chemical change
physical: result in changing the form of a substance, without altering its chemical composition
chemical: change one substance into a new substance with different properties and compositions
intensive vs. extensive properties
intensive: DO NOT depend on the amount of matter present
- ex. boiling point, color, temperature, luster, hardness
extensive: dependent on the amount of matter present
- ex. volume, mass, size, weight, length
volume
amount of space an object occupies
density
ratio of mass of object to volume (d =m/v)
density is intensive property, that does not change w/ matter)
precision vs. accuracy
precision: agreement among several measurements (reproducibility)
accuracy: agreement of a measurement with the true value
2 types of errors
random errors & sytematic errors
random error: caused by factors which vary from one measurement to another (ex. measuring height with slightly different postures)
systematic error: indicates repeated error in the same direction (ex. instrument calibrated or used incorrectly)
avg mass formula
sum of (fractional abundance x isotopic mass)
converting from celcius to kelvin
add 273.15 to C
uncertainty
estimate of amount by which measruement differs from true value
Dalton’s Atomic Theory
(5 parts)
- matter is comprised of tiny particles called atoms
- atoms of a given element are identical
- atoms of different elemtns differ from each other
- chemical compounds are formed when atoms of different elements combine w/ each other
- chemical reactions involve reorganization of the atoms
law of conservation of mass
matter cannot be created or destroyed
law of definite proportion
compounds always contain the same proportion of elements by mass
water will always contain 2 H atoms and 1 O atom
J.J. Thomson
- discovered the electron
- studied electrical discharge in cathode ray tubes
- known for plum pudding model
- determined the charge to mass ratio of electrons (every electron has neg charge)
think jj sounds so electric
Robert Milikan
- discovered what the charge of an electron was
- famous oil drop experiment
- would shoot x rays to the oil drops and the oil drops would basically float
think milk and oil dont mix so milkman brought the charge
plum pudding model
electrons and protons just scattered all throughout, no specific central structure
think jiggly w no structure
radioactivity
+ 3 types of radioactive emission
in late 1800s, scientists found that some elements produce high-energy radiation
3 types:
gamma rays: high energy “light”
beta particles: high speed electrons
alpha particles: posseses a 2+ charge
Ernest Rutherford
- discovered the nucelus
- performed experiments to test plum pudding model
- dense positively charged core
- threw beam of alpha particles at thin metal foil and some of them would go to the middle and just completely shift course
think ruth is the center of my life
what makes atoms different?
2 things
- number of electrons
- arrangement of electrons
isotopes
atoms w/ same number of protons and electrons, but different number of neutrons
fixed volume & fixed shape for solid, liquid, gas
solids: fixed volume & shape
liquids: fixed volume, no fixed shape
gases: no fixed volume, no fixed shape
representation of atom w/ atomic number 84 & mass 206
206 Po
84
mass number on top, atomic number on bottom
calculating # of electrons, protons, & neutrons from mass # & atomic #
atomic # = # of protons & electrons
mass # - # of protons = # of neutrons
formula for atomic mass
sum of (fractional abundance x mass of isotope)
electromagnetic radiation
fancy word for light
energy that behaves like a wave and travels at the speed of light in a vacuum
speed of light in a vacuum
2.998 x 10^8 m/s
the 4 characteristics of waves
- wavelength
- frequency
- amplitude
- speed
characteristics of waves
wavelength
the distance between 2 consecutive peaks in a wave
symbol: λ (lambda)
characteristics of waves
frequency
number of cycles per second that pass through a point in space
symbol: ν
unit: 1/s or Hz (hertz)
characteristics of waves
amplitude
magnitude of the wave’s displacement
(the size of the peak of that wave)
characteristics of waves
speed
how fast the wave travels
random side note on slides
amplitude of sound wave analogous to __________
volume
the louder the sound, the greater the amplitude
relationship b/w wavelength and frequency
inversely related
- wavelength halves = frequency doubles
only true for light, sound waves don’t behave the same
formula for speed of light, wavelength, and frequency
c = λv
c = speed of light
λ = wavelength
v = frequency
the electromagnetic spectrum
- red are the lowest energy levels (on the right)
- higher the frequency, higher the energy
- increasing energy and frequency going to the left
- increasing wavelength going to the right
that random chart looking thing where it goes from blue to red
interference
2 waves come into contact with each other
2 types of interference
- constructive: 2 waves that are IN PHASE (same peaks & troughs) add together
result: higher amplitude - destructive: 2 waves that are OUT OF PHASE (perfectly misaligned, their peaks & troughs match up)
result: balance out and becomes straight line
standing waves + nodes
waves that remain constrained in a region of space (not moving in space but have oscillations like a guitar string)
- nodes: spaces along standing waves which are not in motion
translation wave
waves that are not moving but amplitude keeps changing because of interference
the ultraviolet catastrophe
- late 1800s to early 1900s
- physics at that time couldn’t explain why hot objects didn’t give off infinite amount of UV light
- led to Planck’s theory that energy can only exist in discrete “packets”
max planck’s observations + formula
energy is quantized
- energy can be gained or lost only in multiples of hv
ΔE = nav
ΔE = change in energy for a system
n = any integer
h = Planck’s constant (6.626 x 10^-34 Jxs)
v = frequency of electromagnetic radiation
the photoelectric effect
phenomenon in which electrons are emitted from the surface of a metal when light strikes it
- explained by Einstein
properties of the photoelectric effect
- no electrons are emitted by metals below a specific threshold frequency, regardless of light intensity!
- for light with frequencies greater than v0, # of electrons emitted increases with increasing light intensity
- for light with frequencies greater than v0, the kinetic energy of electrons emitted increases with increasing light frequency
basically saying that intensity (brightness) of light determines the number of photoelectrons, while frequency (color) of light determines energy
photons + relationship of photons & light
stream of “particles” of electromagnetic radiation
- intensity of light is a measure of the # of photons present in the beam (more intense light = more photons)
- energy of photons is directly proportional to frequency of light
significance of E = mc² + derived equation
- shows that energy and mass are related
E = hc/λ
continuous vs. line spectra
continuous spectra result when white light passes through a prism (contains all wavelengths of visible light)
line spectra display discrete wavelengths of light (specific bands showing, not the entire spectrum)
atomic spectrum for hydrogen
when energy is applied to hydrogen gas, hydrogen molecules (H2) absorb energy and some molecules are split into atoms (H)
- electrons are excited
- electrons don’t like staying at high states wanna go lower, energy is released when they go lower
hydrogen emission spectrum
1/λ = -R (1/ (n final)^2 - 1/
(n initial)^2)
R = 1.097 x 10^7 1/m
Bohr Model for the H-atom
- electrons in hydrogen atoms orbited the nucleus in certain energy levels
- extended Planck’s idea that light can only exist in specific intervals to electrons
- an electrons’ energy level is related to the energy level it occupies (further or closer to nucleus dictates how much energy it has)
electron moves further from nucleus = energy absorbed
electron moves closer to nucleus = energy released
bohr model equation
E = -2.179 x 10^-18 J (Z^2/n^2)
Z = nuclear charge (+1 for H)
n = any integer
drawbacks of the Bohr Model
- insufficient for explaining atoms other than Hydrogen
- in reality, electrons do not move around atomic nuclei in circular orbits
(but Bohr spurred quantum mechanics)
maximum # of electrons using the quantum numbers
n principal level - 2n^2 is the formula to find # of electrons possible
ex. n = 2, 2(2)^2 = 8
- if ms is only one number given, half the n value that u found
- l = 0 is s orbital
- l = 1 is p orbital
- l = 2 is f orbital
- l = 3 is d orbital
if 4 quantum numbers are given, the answer is always 1 b/c 4 quantum numbers can only specify ONE electron
de Broglie equation
every single moving particle (including electron) has a wavelength associated with it
λ = h/mv
h = planck’s constant
m = mass
v = velocity
if mass is larger, denominator is larger so wavelength is smaller = explains why wavelength of macroscopic objects was not sensed bc the wavelength was too small
Davisson-Germer experiment (1927)
- provided strong evidence that electrons behave as waves
- same exact diffraction pattern as waves
- finally ended the debate and the physics world acknowledged this
the Heisenberg uncertainty principle
for any particle, can only know the position & momentum with very limited precision
∆x x ∆ p (mv) ≥ h/4π
(don’t need to memorize this equation)
the Schrödinger equation
used to find the probability of where the electron exists
the electromagnetic spectrum (order of the waves smallest to largest)
gamma rays -> x-ray -> UV -> visible light -> infrared -> microwaves -> radio waves
electron density maps
intensity of color depicts probability value near a given point in space
quantum numbers
n = principal quantum number (orbital’s size, energy, and distance from the nucleus)
l = angular momentum (specifies shape of the orbital) up to n-1 # of subshells increase as l increases
ml = specifies orientation of each orbital in 3D space -l to +l
ms = electron spin always +/- 1/2
nodes
areas with zero probability of finding an electron
- total number of nodes in an orbital is equal to n-1
the Pauli exclusion principle
no 2 electrons in the same atom can have the same set of 4 quantum numbers!
- orbitals can hold a maximum of 2 electrons
like saying 2 people have the same ID number
degeneracy
denegerate orbitals are orbitals with the same energy
in hydrogen, orbitals with the same value for n are degenerate
orbital energy increasing trend
- as energy level (n) increases, energy of orbital increases
- as angular momentum (l) increases, energy of orbital increases too
electron shielding
effect where electron experiences reduction in the effective nuclear charge due to electrons occupying inner energy levels
penetrating power
ability of an electron to get close to the nucleus
- the lower in energy level is more penetrating (n takes precedent)
ex. 4s and 5p –> 4s e- is more penetrating
the Aufbau principle
electrons fill the lowest available energy levels (orbitals) before occupying higher levels
Hund’s Rule
1) electrons fill degenerate (orbitals that have the same energy) singly before pairing
2) unpaired electrons have the same spin
start with spin facing upwards first
- that diagram looking thing where you draw the half up and down arrows to show electrons -
electron configurations & orbital diagrams
electron configurations: represent the arrangement of electrons in orbitals of atoms
orbital diagrams: picture that shows arrangement
valence and core electrons
valence: outermost electrons (includes all of them with the same n value)
core: all the inner electrons (everything but the valence electrons)
condensed electron configurations
in brackets, write symbol for noble gas that comes directly before element, then write configuration for all remaining electrons
special case for electron configuration
Cr’s row and everything in it and Cu’s row and everything in it
bump one electron from s to d
ex. 4s2 5d9 becomes 4s1 5d10
elements in the same group have ______________
similar properties
atomic radius definition
half the distance between the nuclei of 2 atoms of an element
atomic radii trend & why
- increases down groups b/c more orbitals so greater in size
- decreases across periods b/c effective nuclear charge increases, decreasing atomic radius, greater “pull” for electrons
isoelectronic ions
ions with the same number of electrons
trends for ionic radii
- increases down groups
- decreases with effective nuclear charge (for isoelectronic ions)
ionization energy + trend
amount of energy required to remove an electron from an atom to an ion
trend:
- decreases down groups
- increases across periods (left to right)
why is there a deviation in ionization energy trend b/w nitrogen and oxygen?
oxygen has 2 electrons in the same orbital which causes repulsions b/c they’re both negatively charged particles
for that reason, more favorable to remove electrons from oxygen than from nitrogen
electronegativity + trends
ability of an atom to attract electrons
Trend:
- decreases down groups
- increases across periods (left to right)
Dmitri Mendeleev
credited for originally organizing the period table
managed to:
- correct several values for atomic masses
- predict properties of later discovered elements (would put question marks n stuff)
