Chem Unit 1

Question 1

Define electromagnetic spectrum

Answer 1

electromagnetic radiation (light) is a way energy moves. Light energy travels in waves, at the speed of light.

Question 2

In what way do waves move?

Answer 2

Perpendicular to the way it travels

Question 3

Define amplitude

Answer 3

The distance between a wave’s zero to it’s crest

Question 4

Define crest

Answer 4

the highest point of a wave

Question 5

define trough.

Answer 5

the lowest point of a wave

Question 6

define wavelength

Answer 6

the distance between crests; the length of one complete wave cycle

Question 7

define frequency

Answer 7

the number of wave cycles to pass a given point, per unit of time

Question 8

what is the mathematical relationship between wavelength and frequency?

Answer 8

they are inversely proportional/related.

c = speed of light (m/s) —–> 3.0 * 108 m/s
λ = wavelength (m)
v = frequency (hertz, 1/s)

Question 9

describe the relationship between frequency, wavelength, and energy.

Answer 9

lower frequency = lower energy = longer wavelength

higher frequency = higher energy = shorter wavelength

Question 10

atomic emission spectra

Question 11

how do atoms arrange themselves?

Answer 11

electrons arrange themselves to be in the lowest possible energy state.

Question 12

what is the lowest state?

Answer 12

the closest an electron can be to the nucleus.

Question 13

in what way do electrons move when absorbing energy?

Answer 13

they move to a higher energy level, and then as they come back down they emit the energy.

Question 14

define quantized energy.

Answer 14

quantized energy means the electrons can possess only certain, discrete energy values; values between those quantized values are not permitted.

Electron must move from one energy level to another in distinct steps, rather than moving continuously

Question 15

what is an excited state of an atom?

Answer 15

a state where its potential energy is higher than the ground state
–> unstable

Question 16

what happens when the electron returns back to the ground state?

Answer 16

it releases energy that it previously gained in the form of electromagnetic radiation (light).

Question 17

how do atoms gain energy?

Answer 17

tubes filled with gas at low pressure pass through an electric current. Electrons in the gaseous atoms become excited, and then fall back to lower energy levels, emitting a light of distinctive colour.

Question 18

why do gas discharge tubes glow with a different, distinct colour?

Answer 18

electron energy levels are unique for each element

Different types of light are based on how many energy levels there are.

Question 19

list the two steps of an electron gaining energy.

Answer 19

1. excited electrons jump to a new energy level.
2. they fall back down, emitting the distinct colour, as they can only occupy specific spaces and therefore give different emissions

Question 20

when are atomic emission spectras produced?

Answer 20

when excited electrons return to ground state.

discrete photons carrying discrete amounts of energy

Question 21

describe the visible EMISSION spectrum for hydrogen

Answer 21

composed of 4 lines: converge at high frequency.

gas discharge tube, light goes through a slit, which hits a prism, which creates the emission spectrum

v = 410
i = 440
g = 490
r = 660

Question 22

define/describe the continuous spectrum.

Answer 22

• all wavelengths (frequencies within a particular region) are seen
• often represented as the complete ROYGBIV

Question 23

what two regions can you have continuous spectrum in?

Answer 23

1. visible
2. UV

Question 24

describe white light.

Answer 24

white light contains all frequencies in the visible spectrum, so it can be split into a continuous spectrum by a prism

Question 25

what does emissions only existing at certain wavelengths tell us?

Answer 25

electrons cannot occupy anywhere around the spectrum. [?]

Question 26

define a line spectrum

Answer 26

- has two types - emitted radiation is split into a spectrum that only contains emissions at particular wavelengths - gas absorbs different wavelengths that correspond to their energy levels, everything else passes through

Question 27

define an absorption spectrum

Answer 27

- is a kind of LINE spectrum - a heat source that emits a continuous spectrum is placed BEHIND a COLD and transparent cloud of gas - gas absorbs some colours/specific wavelengths - displays missing black lines - the black lines that are "missing" correspond to the emission spectrum In the absorption spectrum there will be gaps. The absorbed photons show up as black lines because the photons of these wavelengths have been absorbed and do not show up.

Question 28

define an emission spectrum

Answer 28

- the gas is heated directly - cloud of hot, transparent gas emitting certain colours - displays coloured lines coloured lines correspond with absorption spectrum

Question 29

describe the Hg, Ne spectrums

Answer 29

Hg: 2v, 1i, 2g, 3y, 2o, 1r (11) Ne: 2i, 3g, 6y, 5o, 4r (20)

Question 30

there is a [limited/non-limited], [specific/non-specific] number of energy quantities (deltaE) that the e- in an atom can lose.

Answer 30

limited, specific

Question 31

falling down a specific distance will always give off the [same/different] amount of energy

Answer 31

same - The “gap” the electron falls down by is dictated by the energy level - Electrons can only be found in specific energy levels, and must remain there except when energy change is applied

Question 32

what are the four different components of energy levels?

Answer 32

1. ground state (n = 1; shell closest to the nucleus) 2. excitation (excited state): give light/heat, somewhere between n = 1 and the largest shell 3. emission: eventually returns back to ground state 4. ionization: when the electron completely leaves an atom due to an excess of energy

Question 33

be able to draw the diagram of energy levels.

Question 34

list the 3 kinds of spectrums that the light emits.

Answer 34

a) LYMAN: electrons returning down to n = 1 emit UV light (HIGH energy). --> biggest amount of energy released b) BALMER: electrons returning down to n = 2 emit visible light c) PASCHEN: electrons returning down to n = 3 emit IR light (LOW energy)

Question 35

define ground state, first excited state, second excited state.

Answer 35

ground state: n = 1 (closest shell to nucleus) first excited state: n = 2 second excited state: n = 3

Question 36

what is the trend for energy levels?

Answer 36

CONVERGENCE: the lines, as demonstrated by energy level diagrams, get closer and closer together, as frequency increases (wavelength decreases) more energy = the higher the energy level (approaching n = infinity). corresponds with the difference of far out electron shells: closer and closer --> as you move away from the nucleus, do not feel attraction as much