AP Chem Unit 1

Crystalline

atoms or molecules are in patterns with long-range, repeating order

Amorphous

atoms or molecules do not have any long-range order

Liquids

atoms or molecules pack about as closely as they do in solid matter, but are free to move relative to each other

• Fixed volume, but not fixed shape

  • Assume shape of container

Gas

1. atoms or molecules that have a lot of space between them and are able to move relative to one another

   • compressible

Solids

molecules are packed closely together in fixed locations

• fixed volume and rigid shape

Pure substance

• made up of only one component

  • can be individual atoms, or groups of atoms joined tg

Element

substance that cannot be chemically broken down into simpler substances (type of pure substance)

Compound

substance composed of two or more elements (type of pure substance)

mixture

made up of two or more components in proportions that can vary from one sample to another

Heterogeneous mixture:

comp varies from region to another

Homogenous

same composition throughout

Decanting

ex. water and sand - carefully pouring off the water into another container

allowing denser to settle at the bottom and pouring the rest off

Distillation

mixture is heated to boil off the more volatile liquid

Volatile

easily vaporizable

When composed of an insoluble solid and a liquid, separated by

filtration

Physical changes

• changes that alter only state or appearance, not composition

  • can change state, as long as it is the same atoms

Chemical changes

• atoms rearrange, transforming og substances into diff substances

Physical property

a property that a substance displays w/o changing its composition

Chemical property

• a property that a substance displays only by changing its composition via a chemical change

  • ex. corrosiveness, flammability, acidity, toxicity, etc.

  • only chemical examination can confirm whether a particular change is physical or chemical

Kelvin

• measure of temperature

  • also called absolute scale bc avoids negative temp

  • 0k is coldest temp possible (-273.15 C or -459 F)

  • K = C + 273.15

temperature

• measure of the average kinetic energy of the atoms or molecules that compose the matter

Intensive property

one that is independent of the amount of the substance

Extensive property

• one that depends on the amount of the substance

  • ex. if you know only the mass of a sample of gold, that info alone will not allow you to identify it as gold

Accuracy

• how close the measured value is to the actual value

Precision

how close a series of measurements are to one another or how reproducible they are

Wave particle duality

• certain properties of light are best described by thinking of it as a wave, while others are best described thinking of it as a particle

Electromagnetic radiation

type of energy embodied i n oscillating electric and magnetic fields-what light is idk

Electric field

a region of space where an electrically charged particle experiences a force

• Waves

• characterized by amplitude and wavelength

Amplitude

• vertical height of a crest or depth of a trough

  • determines light’s intensity or brightness - the greater the amplitude the greater the intensity

Wavelength (λ):

• distance between adjacent crests

  • measured in meters

Frequency (v):

• number of cycles that pass through a stationary point in a given period of time

• inversely prop to wavelength - the farther apart the crests, the lower the number of crests that pass a fixed location per unit time

relationship between frequency and wavelength

• equation v = c/λ

• as wavelength increases, the frequency decreases

Visible light

• light that can be seen by the human eye

  • wavelength determines color

Electromagnetic spectrum

• all wavelengths of electromagnetic radiation

Electromagnetic spectrum from shortest to longest wavelength

Gamma ray

x ray

ultra violet radiation

visible light

infrared

microwaves

radio waves

Visible light

• ranging from violet (shorter wavelength higher energy) to red (longer wavelength lower energy)

Infrared Radiation

heat when you place your hand near a hot object

interference

• when waves interact with each other in a characteristic way like building each other up or aligning

constructive interference

• if two waves of equal amplitude are in phase when they interact → wave with twice the amplitude

destructive interference

 if two waves are out of phase, the waves cancel

out of phase

• they align so that the crest from one source overlaps with the trough from the other source

Diffraction

• when a wave encounters an obstacle or a slit that is comparable in in size to its wavelength, it bends or diffracts around it

interference pattern

the result of the diffraction of light through two slits separated by a distance comparable to the wave length of light coupled with interference results

Photoelectric effect

• observation that many metals emit electrons when light shines upon them

• sceintists found that a high frequency, low intensity light produces electrons without the predicted lag time

Threshold frequency

threshold below which no electrons are emitted from the metal, no matter the duration

Albert Einstein

• determined that light energy must come in packets

• suggested that light was lumpy rather than continuously variable

Energy is

quantized

Quantized Model

• electrons orbit the nucleus in fixed paths (called energy levels or shells)

• each energy level (n) has specific radii (energy)

  • these energy levels are quantized

valence shell

the outermost principal energy level with electrons

valence electrons

• electrons located in the valence shell

Niels Bohr's Postulates for an atom

1. electrons can only exist in specific energy levels (n), not inbetween

2. shells closest to the nucleus are more stable (less energy)

3. electrons can absorb a photon with exactly the right amount of energy that would put it in a higher energy level

4. electrons in excited states will emit photons when they spontaneously drop to lower energy levels

ground state

the lowest possible energy state for an atom

excited state

1. when the electrons are put in a higher energy level

2. electrons in excited states will emit photons when they spontaneously drop to lower energy levels

Law of Conservation of Mass

mass/matter cannot be created nor destroyed; the mass before and after a chemical reaction is the same

Law of Definite Proportions/Constant Composition

a pure chemical compound always contains the same elements in the same fixed proportion by mass

Law of Multiple Proportions

if two elements form more than one compound the mass of one element will combine with the mass of the other in a ratio of small whole numbers

isotopic notation

isotopes

atoms of the same element with different masses

• isotopes have different numbers of neutrons

• isotopes have different numbers of neutrons

weighted average

• atomic mass=(%1)(mass 1)+(%2)(mass 2)+(%3)(mass 3).....