Chemistry Test -- Chapter 11 Test (Atomic Structure and Electromagnetic Radiation)

what is the ground state of an atom?

• lowest energy state of an atom

• all electrons are in the lowest possible energy level (orbital)

• stable

• not absorbing or realizing any energy 

what is the excited state of an electron?

• this occurs when an atom absorbs energy

• one or more electrons move to higher energy levels away from the nucleus 

• unstable 

what happens to an atom to get from the ground state to the excited state and vise versa?

• an atom absorbs energy then electrons jump from ground to excited state

• electrons fall back down to ground state and release energy as light (photons)

• the color of light emitted depends on the amount of energy released 

why do atoms have different atomic emission spectra with different intensities?

different elements —> different energy levels —> different wavelength

different numbers of transitions —> different intensities (brightness)

• each element has a unique electron arrangement and because of this energy levels where electrons exist are different for every element

• when electrons fall back from excited states to lower energy levels, they release energy as light and that determines the color (wavelength) of light

• different intensities happen because more electrons make the same transition (higher intensity) or fewer excited electrons make a transition (lower intensity)

why is the atomic spectra “fingerprints” of an element?

• each element has a unique and unchangeable set of energy levels for it electrons

• when electrons absorb energy and fall back to lower levels, they emit light at specific wavelengths

• because the pattern of lines in the spectrum is unique to each element, it can be used to identity the element

how do fireworks work?

• fireworks have small tubes called aerial shells which have gunpowder and stars

• stars have oxidizing agents, fuel, metal-containing colorant, binder

• the fuse is lit and the gunpowder exploded, pushing the aerial shell into the sky

• a time-delay fuse ignites the bursting charge causing it to explode and ignite the stars

• heat and gas is released and the burning stars go in different directions 

• loud boom caused by rapid expansion of hot gases (faster than the speed of sound)

what gives fireworks different colors?

• metal salts in the stars 

• the heat excites the electrons when it explodes and when they fall back down, they release energy as light 

what are two ways fireworks give off light? explain.

• incandescence: happens when a substance gets so hot it glows (red, orange, yellow, white)

• luminescence: happens when electrons in metal atoms absorb energy and then release it as light when they go back to ground state (doesn’t depend on high temperature)

know how to find the wavelength, frequency, and energy of various types of EMR.

page 32 of notebook 

what is the dual nature of EMR and electrons?

• light exhibits both wave and particle-like behavior

• each particle carries a quantum of energy 

• a photon is a particle of electromagnetic radiation having zero mass and carrying a quantum of energy 

what is the photoelectric effect? what did Einstein conclude of it? 

• emission of electrons from a metal when light shines on the metal

• light must be at a minimum frequency to knock an electron loose from the metal 

• Einstein said that EMR is absorbed by matter only in whole numbers of photons 

who is Max Planck?

• studied emission of light by hot objects

• proposed that hot objects do not emit electromagnetic energy continuously, but in small, special packets called quanta 

• a quantum is the minimum quantity of energy that can be lost or gained by an atom 

what is the double slit experiment? how does it relate to EMR and electrons?

• double slit experiment: barrier with two narrow slits had light shone through it and it created a pattern of light and dark bands showing light waves 

• electrons were shone through because that is light

• EMR and electrons act like waves and particles

• EMR: this is an interference pattern and waves overlap (crest to crest — bright, crest to trough — dark) —> light behaves like a wave 

• electrons: the pattern changes to two lines —> electrons behaving like particles