midterm exam Flashcards by meagan b

what is chemistry?

the study of the composition and structure of matter in the changes they undergo

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briefly explain the scientific method

observe- collect data, experiment, communicate

theory- tests are always done with theories

test- observing, testing and theories can go back and forth if more/new data is needed

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what is the difference between an endothermic and exothermic reaction?

endothermic- absorb energy, feels cold

exothermic- release energy, feels hot

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list one intensive and one extensive physical property of a sample of water

intensive- color

extensive- heat

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which piece of equipment do you use to find the mass? Which piece of equipment do you use to find the volume?

use a balance to find the mass, use a graduated cylinder to find the volume

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list the indicators of a chemical reaction

unexpected change in color
a gas is released
energy is released or absorbed
the formation of a precipitate

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List the units to measure heat in the units to measure temperature. are heat and temperature of the same thing?

heat- J
temperature- °C

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what is an atom? what one factor determines an atom’s identity?

the smallest particle of an element that retains the chemical identity/properties of that element

atomic number

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John Dalton wrote the first atomic theory. what two points in his three were later prove to be false? explain why each is false

atoms are not subdivided created or destroyed and a chemical reaction- changed to: atoms cannot be subdivided created or destroyed. (this was because of nuclear reactions

atoms of a given element have the same size, mass, and other chemical properties- changed to: atoms of the same element have the same chemical properties (this was because of isotopes which differ in mass and size)

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how did Thompson use the cathode ray tube experiment to determine that electrons have a negative charge?

The cathode ray was repelled by negative charge, meaning the cathode ray had a negative charge

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how did Thompson use the cathode ray to be experiment to determine that electrons are particles?

when a paddle wheel was placed on the cathode ray it spun, showing it was made of particles

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how did Millikan use the oil drop experiment to determine the charge of an electron?

he adjusted the voltage so the charge drop would stay in mid air between the two plates

force~(charge on drop)(voltage charge) to find it; where force and voltage charge were given and you could solve for charge on drop

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how did Millikan determine the mass of the electron?

he used the charge and Dalton’s ratio (in the oil drop experiment)

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after the cathode ray tube and oil drop experiments, scientists knew that atoms are neutral yet electrons are negative. what conclusion regarding atoms could they draw from this?

there must be something positive in the atom that could balance out the negative electrons and make the atom neutral

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briefly explain the plum pudding model of the atom

it modeled an atom with a positive charge spread throughout it with the negative electrons scattered. alpha particles passed by without repelling

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what would have been observed in the gold foil experiment if the plum pudding model were true?

alpha particles would pass by without interruption or repelling

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how did Rutherford determine that the nucleus has a very large mass?

the alpha particle bounced back after hitting the nucleus, (the nucleus had to be large enough for it to bounce back)

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how did Rutherford determine that the nucleus is positive?

positive alpha particles repelled from the nuclei as they passed, things with like charges repel from one another

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how did Rutherford determine that the nucleus is very small?

it only hit 1 out of 8,000 times, if it were much larger it would hit a lot more often

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list the three subatomic particles with their masses, charges, and locations

protons- charge: +1, mass (amu): 1, location: nucleus

neutrons- charge: 0, mass (amu): 1, location: nucleus

electron- charge: -1, mass (amu): 0, location: electron cloud

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what what is the strong nuclear force?

the force that holds the nucleus (of an atom) together

why are decay equations not written for gamma decay?

no particles are released in gamma decay, (only energy is released)

list the types of electromagnetic radiation in order from highest frequency to lowest frequency

gamma radiation
x-rays
ultraviolet radiation
visible light
infrared radiation
micro waves
radio waves

what is wavelength? what is frequency? which variable does the energy of a wave depend on?

wavelength- the distance from one crest of a wave to another

frequency- how many waves pass a given point per second

the energy of a wave depends on the frequency of a wave

briefly explain Einstein’s photoelectric experiment. what was his conclusion?

he shone red light and purple light on metal. if the red light was a wave, the metal would have. soaked up enough energy to create a current (but it didn’t); only the purple light had enough energy to conduct a current he concluded that light came in the form of particle streams

how do quanta and photons compare

quanta and photons compare because a quanta is a finite amount of energy, and a photon. is a quanta of light

what is the difference between quantized and continuous? is energy quantized or continuous?

quantized- only specific, certain values (are accepted) continuous- all values (are accepted energy is quantized

explain the activity of electrons when heated in a flame

electrons reach a higher energy level and go into an excited state when heated in a flame

what is spectroscopy?

the identification of atoms through the emission spectra

the Bohr Model of the atom seems to make sense. what was its problem

it only worked for hydrogen; it could not explain the line spectra of elements with more than one electron; it treated electrons as particles

what is the difference between an orbit and an orbital?

orbit- an exact, definite location of an electron outside the nucleus oribitz- a predictable, but not definite location on an electron outside the nucleus

list the four quantum numbers with their descriptions and possible values

principle quantum number- describes: the energy level of an orbital, possible values: 1, 2, 3, 4, 5, 6, 7, 8 orbital quantum number- describes: the shape of an orbital, possible values: s, p, d, f magnetic quantum number- describes: the orientation of the orbital on the x/y/z axis, possible values: x, y, z spin quantum number- describes: the spin of the electron(s), possible values: +1/2, -1/2

which group is the most reactive? which group is the least reactive?

most reactive- alkali metals | least reactive- noble gases (are nonreactive)

what is ionization energy? which group has the largest ionization energy?

the energy required to remove one electron from an atom largest IE: group 18

equation for first ionization energy. which group has the lowest first ionization energy?

A + energy —> e- + A+ lowest group

what happens to ionization energy as you move down a group? explain

IE decreases because you are removing electrons further and further from the positive nucleus

write the equations for the second and third ionization energies

second IE: A+ + energy —> e- + A^2+ third IE: A^2+ + energy —> e- + A^3+

what is electron affinity? write the equation for negative electron affinity

the energy charge that occurs when adding an electron to an atom negative EA equation: A + e- —> energy + A-

which group has the highest positive electron affinity? why?

highest positive EA: group 18 because it already has a full octet

what is electronegativity?

an atom of a compound’s tendency to draw electron towards it

which group has the highest electronegativity values? what happens to electronegativity as you move down a group?

highest EN values: group 17 as you move down a group, EN decreases

what happens to atomic radius as you move across a period? explain

as you move across a period, atomic radius decreases. this is because no new energy levels are added and the nuclear charge increases, so the electrons are being drawn in towards the nucleus

what is a cation? how does its size compare to a neutral atom?

a positive ion it is always smaller in size compared to its neutral atom

what is an ionic bond? what is a covalent bond?

ionic bond- the force of attraction between oppositely charged ions, no electrons are shared covalent bond- a bond in which electrons are shared/distributed

two elements form a compound. assuming there are partial charges present, how can you tell which atom has the partial negative charge?

whichever atom has the highest electronegativity, or pull on electrons, has the partial negative charge

in terms of electrons, what is the difference between a polar covalent bond and a nonpolar covalent bond

polar covalent bond- a bond where electrons are evenly distributed nonpolar covalent bond- a bond in which electrons are evenly shared

what is the main reason that elements and compounds undergo chemical reactions?

so that atoms can become more stable

why must chemical reactions be balanced?

because atoms cannot be lost or gained in a chemical reaction

what is a mole?

the amount of a substance that contains 6.022x10^23 particles

what is molar mass? what is formula mass?

molar mass- the mass, in grams of one mole of a substance formula mass- the mass, in amu, of one particle of a substance

compare and contrast one mole of magnesium and one mole of aluminum

one mole of magnesium and one mole of aluminum have the same amount of atoms (6.022x10^23 atoms), but have different masses (Mg = 24.305 g, Al = 26.982 g)