Exam 1 Flashcards
4 states of matter for molecules:
SOLID
Solid: fixed position, vibrate, can’t leave position in crystalline lattice (defined shape)
4 states of matter for molecules:
LIQUID
Liquid: glued together, can slide past each other, vibrate & rotate (shape of container)
4 states of matter for molecules:
GAS
Gas: free to move, occupy entire volume container (shape & volume of container)
4 states of matter for molecules:
PLASMA
Plasma: “ionized gas” contains electrically charged particles (lightning strikes, TV)
Allotrope
Allotropes: different forms of same element
ie. oxygen gas (O2) –> ozone gas (O3)
Pure substance:
Pure substance: constant & uniform composition
Element:
Element: molecules contain only 1 type of atom
(pure sub. cannot be broken down into simpler substances by chemical changes
O2
Compounds:
Compounds: combining different atoms
(pure sub. can be broken down into simpler substances by chemical changes)
H2O
Mixture:
Mixture: 2+ types of matter (molecules) that can be present in varying amounts and can be separated by physical changes (ie. evaporation)
Homogenous mixture:
Homogenous mixture: uniform composition, appears visually same throughout
(“solution” ie. air)
Heterogeneous mixture:
Heterogeneous mixture: composition varies from point to point
distinct clumps different molecules/substance - oil & water
Table used to classify matter:
Physical properties:
Physical properties: can be observed without changing a substance into another (reversible)
mass, volume, density, boiling pt, solubility, color, softness, something melts
Intensive physical property
Intensive: independent of amount of substance present
boiling pt, density, color
Extensive physical property
Extensive: depend on amount substance present
weight, mass, length
Chemical properties:
Chemical properties: observed when matter undergoes changes in chemical composition
flammability, corrosiveness, reactivity with acid
(hint look for terms with “reacting, changing, burning”)
Changes in matter: Physical change
Physical change: don’t change composition of substance and no new substance is formed (wax melts, magnetizing solids)
Changes in matter: chemical change
result in formation of new substance with different chemical properties (combustion, oxidation)
Law of conservation of matter:
Law of conservation of matter: there is no detectable change in total quantity of matter present when matter converts from one type to another (chemical change), of changes among solid, liquid, gaseous states (physical change)
separation of mixtures techniques
Filtration: liquid separated from a solid
Substances with diff solubility can be separated using suitable solvent (sand & salt)
Substances with diff boiling points separated using distillation or evaporation
Sublimation: direct conversation from solid → gas (ammonium chloride)
Signifiant figure rules
- All non-zero digits = significant
Zeros: - Left = not significant
- Middle = significant
- Right = significant after decimal point
Rounding number rules
Adding/subtracting: same # decimal places as the # with least decimal places
Multiplying/dividing: same # of significant figures as # with least sig figs
If digit dropped < 5 (round down) if > 5 (round up)
If digit dropped = 5 (round up or down whichever yields an even value for the retained digit)
What can be used to show a larger number of sig figs?
scientific notation
All measurements have some degree of uncertainty, not exact. What are the only EXACT numbers?
counting, definition, unit conversion (infinite # sig figs, no uncertainty)
They don’t limit # sig figs in a calculation
Accuracy vs. Precision
Accuracy: very close to the true/accepted value
Precision: similar results when repeated in the same manner
Density
density = mass / volume
At particular temp & pressure, density of substance is characteristic property → often used to identify unknown substance
Determine density of irregular object: use volume water displaced in beaker
Atom:
Atom: smallest unit of an element that can participate in chemical change (indivisible)
Element:
1 type of atom
mass is a characteristic feature that is the same for all atoms of that element
Molecule:
Molecule: 2+ atoms joined by chemical bonds (could be same atom or different)
Dalton’s atomic theory:
wrong, but laid foundation for future work
- All matter is made up of tiny particles called atoms (indivisible & indestructible)
- Atoms of an element are identical in size, mass, chemical properties
- Atoms combine to form compounds in whole number ratios
4.Atoms of element cannot change into atoms another element (only rearrange)
Which chemical reactions are not possible according to Dalton’s atomic theory?
Dalton believed: atoms of a given element retain their identities in chemical reactions
CCl4 –> CH4 (not possible)
Cathode ray tube, J.J. Thomson:
Early experiment: showed electrons small negatively charged particles inside atom –> plum pudding model
Later experiment using electric filed & magnet: measure charge to mass ratio of electron
Oil drop experiment, Millikan:
measure charge on small droplets of oil by suspending them between pair of electrically charged plates
charge of oil droplet are multiples of the electron charge : e-=1.60210-19C
Alpha-ray scattering, Rutherford:
alpha particles and gold foil → discovery of nucleus in atoms (disproved the plum pudding model → let to development of modern atomic model)
Atoms much larger than nuclei & mostly empty space inside atom occupied by electrons
Nucleus has protons & neutrons (which are much much heavier than electrons) → nucleus accounts for most of an atom’s mass but very little of its size
Useful in determining the nuclear charge of the atom b/c revealed most of atom’s mass & + charge concentrated in nucleus
In a neutral atom, where does most of the mass come from?
mass atom comes from protons & neutrons, mass electrons is negligible
Rutherford’s model of atom:
- All + charge & mass concentrated inside nucleus (tiny region)
- Negatively charged particles revolve around nucleus in circular path
- Electrostatic force attraction between proton & electrons holds atom together
What were limitations to the Rutherford model of atom?
Failed to explain:
1. Stability of an atom
What did Niels Bohr study?
electromagnetic radiation
Atomic number (Z):
protons in nucleus (found in periodic table)
Neutral atom: electrons = protons
Mass number (A):
A = protons + neutrons
Nuclear symbol:
represents nucleus of an isotope
Mole:
number of atoms/molecules in a bulk sample of matter
Molar mass:
Molar mass: mass in grams of 1 mole of that substance [gmol]
Can the number of protons and neutrons in the nucleus of an atom vary?
Number or protons in the nucleus defines the element therefore is the same for all atoms of an element. However, the number of neutrons in an atom can vary → isotopes.
Isotopes:
same #protons, different #neutrons
atoms with same atomic number (Z) but different mass number (A)
carbon 12, 13, 14
Isotopes have same chemical but different physical properties (due to differences in mass)
Percentage abundance of isotopes
Atomic mass of isotopes
weighted average of isotopic masses of all the naturally occurring isotopes of an element (decimal value)
Electromagnetic (EM) radiation:
oscillating electric & magnetic field perpendicular to each other & direction propagation (ie. visible light from sun, microwaves, x-rays)
Characteristics of EM radiation: wavelength (λ)
distance between 2 consecutive peaks/troughs
Characteristics of EM radiation: frequency (ν)
cycles pass through given point / second
1/sec = Hz
Amplitude (A):
height of peak, corresponds to brightness/intensity
What speed do all types of EM radiation travel?
speed of light
c = 3 x 10^8 m/s
Relationship between frequency & wavelength
Electromagnetic spectrum: order decreasing λ
microwave > infrared > visible > ultraviolet > x-ray > gamma ray
MIVUXG
Memorize wavelength range of visible light:
ROYGBIV
red (largest λ) –> violest (smallest λ)
Photoelectric effect (equation)
light wave is particulate in nature, consisting of small packets of energy called photons
Photoelectric effect (experiment & findings)
Electrons can be ejected from surface of a metal when light have a frequency greater than some threshold shone on it
light with > threshold frequency, KE of emitted electrons increased linearly with frequency of light
KE of emitted electrons didn’t change as intensity light increased
electrons emitted directly proportional to intensity light
Photoelectric effect: threshold frequency (v0)
min frequency of light needed to eject electrons
Relationship between threshold frequency and work function
Photoelectric effect: max KE of emitted electrons
Graph of work function vs. frequency of light (photoelectric effect)