Chem 152 - Chapter 9 Electrons

Front 1

Diatomic Elements

Back 1

Hydrogen (H2)
Nitrogen (N2)
Oxygen (O2)
Fluorine (F2)
Chlorine (Cl2)
Iodine (I2)
Bromine (Br2)

Front 2

Explaining Diatomic Bonding

Back 2

-These seven elements (H, N, O, F, Cl, Br, and I) are called the diatomic elements because, as pure elements, they form molecules containing two atoms

-no additional bonding is needed.

-covalent bonding between atoms of the same element

Front 3

Bohr Model and Quantum-Mechanical Model

Back 3

-explain inertness, reactivity and the perodica law of elements

-explain how electrons exist in atoms and how those electrons affect the chemical and physical properties of elements

Front 4

What is Light?

Back 4

-Light is electromgnetic radiation

-A type of energy that travels through space at a constant speed

-light is not matter

Front 5

What is the speed of light?

Back 5

3.0 x 10^8 m/s (186,000 mi/s)

Front 6

Speed of Light vs Speed of Sound

Back 6

Light travels faster hence fireworks ... explosions are heard after light appears

Front 7

Wavelength

Back 7

- the distance betwen adjacent wave crests

-Lambda

-determines color of visble light

Front 8

Frequencies and Wavelengths

Back 8

Higher frequencies have shorter wavelengths, and lower frequencies have longer wavelengths.

Front 9

Longest - Shortest Wavelengths

Back 9

Red
Orange
Yellow
Green
Blue
Indigo
Violet

Front 10

Red vs Violet

Back 10

Red has longest wavelengths in visble light

Violet has the shortest wavelength in visible light

Red = 750nm

Violet = 400nm

Front 11

Why is a red shirt red?

Back 11

-the shirt reflects red light

-shirt absorbs all other color except red

Front 12

Frequency

Back 12

-number of cycles of crests that pass through a stationary point in one second

Front 13

Wavelengths and Frequency

Back 13

-Inversely related

-shorter the wave length the higher the frquency

Front 14

Redefining Light

Back 14

-Einstien described light as particles

Front 15

Photon

Back 15

-a particle of light

-a single packet of light energy

-amount of energy carried by packet depends on the wavelength of the light

Front 16

Energy in Photon

Back 16

Depending on the wavelength of the light increases of decreases the amount of energy carried in the particle

Front 17

If the wavelength of light is short what can be proposed about the characteristics of light

Back 17

-higher Frequency = more cycles passing through a point in one secon

-if on the spectrum of visible light closer to violet

-greater energy // crests closr together

Front 18

Example of Photon Energy

Back 18

violet carries more energy per photon because crests are closer to together

shorter wave lengths = higher energy

Front 19

What is white light?

Back 19

White light is the effect of combining the visible colors of light in equal proportions.

Front 20

What is the visible spectrum

Back 20

The visible spectrum is the portion of the electromagnetic spectrum that is visible to (can be detected by) the human eye.

-small portion of electromagnetic spectrum

Front 21

Visible Spectum in terms of wavelengths and frequencies

Back 21

A typical human eye will respond to wavelengths from about 390 to 750 nm.[1] In terms of frequency, this corresponds to a band in the vicinity of 400–790 THz.

Front 22

Ranges of Electromagnetic Waves

Back 22

-10^5m
(low enegy; radiowaves)

to

- 10^-16m (high energy; gamma rays)

Front 23

Gamma Rays

Back 23

-electromagnetic radiation with the shortest wavelength/ highest frequency/highest energy

-high energy can damage biological molecules

-produced by stars and unstable atomic nuclei on earth

Front 24

X Rays

Back 24

-lower energy than gamma rays = higher wave length and lower frequency than gamma rays

-pass through substances that block physical light

Front 25

Ultraviolet light (UV Light)

Back 25

-in between visible light and X-Rays

-emitted from sun can cause damage in excess

Front 26

Visible Light

Back 26

-Violet(short) to Red(long)

-photons of visble light do not damage biological molecules

-cause our eyes to reaarange themselves to send signals to our brains

Front 27

Infrared Light

Back 27

-has longer wavelengths than visible light

-all warm bodies emit infrared light

-longer wavelengths than visible light

Front 28

Microwaves

Back 28

-longer wavelengths than infrared light

- lower energy per photon than visible light and infrared radiation

-used for radar and microwaves

-effciently absorbed by water

Front 29

Radiowaves

Back 29

transmit signals (radio, television, cell phones, etc.. )

Front 30

Atoms emitt color when...

Back 30

when an atom absorbs energy-- in the form of heat, light, or electricity -- it often re-emits that energy as light

Front 31

Emission Spectrum

Back 31

The emission spectrum of a chemical element or chemical compound is the relative intensity of each frequency of electromagnetic radiation emitted by the element's atoms or the compound's molecules when they are returned to a ground state.

-constituent wavelengths

Front 32

continuous spectrum

Back 32

-intensity is uninterupted or smooth across the range

Front 33

What property of atoms changes the emission spectrum?

Back 33

"Since the emission of light in atoms is related to the motions of electrons within the atoms, a model for how electrons exist in atoms muct account for these specta."

Front 34

Bohrs Model

Back 34

-electrons travel around the nucleus in circular orbits that are similiar to planetary orbits around the sun

- orbit only at fixed, specific distaces

analogies- step ladder

Front 35

Energy of each Bohr orbit ...

Back 35

specified by a quantum number (quantized)

Front 36

Quantum Number

Back 36

Quantum numbers describe values of conserved quantities in the dynamics of the quantum system. Perhaps the most peculiar aspect of quantum mechanics is the quantization of observable quantities. This is distinguished from classical mechanics where the values can range continuously. They often describe specifically the energies of electrons in atoms, but other possibilities include angular momentum, spin etc. Since any quantum system can have one or more quantum numbers, it is a rigorous job to list all possible quantum numbers.

Front 37

Electrons in orbit

Back 37

As long as an electron remains in a given orbit, it does not absorb or emit light, and its energy remains fixed and constant.

- farther from nucleus greater the energy

Front 38

Atom absorbs energy...

Back 38

-fixed electron orbit excited to an orbit farther away

-higher away from nucleus; higher energy

-new configuration less stable and electron quickly falls back or relxes into lower orbit

-electron wants to be closer to nucleus

-as it relaxes releases photon of light -- quantum of energy = difference between two orbits

Front 39

Quantum of Energy

Back 39

-percise amount of energy

-the amount of energy it takes for a electron to get from one energy level to the next.

The energy of an electron bound to an atom (at rest) is said to be quantized, which results in the stability of atoms, and of matter in general.

Front 40

Atom Absorbing Energy by the Numbers

Back 40

1. Electron in fixed orbit is excited; promoted to next orbit; higher energy

2. Atom becomes less stable in new configuration

3. Electron relaxes back to lower energy orbit

4. releases a photon of light containing the quantum of energy between two orbits

5. emitted photon correlates with a wavelength

6. hence light emitted by excited atoms consists of specific lines at certain wave lengths

7. those wavelengths relate to the transistion between orbits

Front 41

The Hydrogen Example

Back 41

- line at 486 nm hydrogen emission spectra corresponds with electron going from n=4 to n=2

n=3 to n=2 produces less energy shorter wave length

-Tranistions between orbits that are closer together produce lower energy (longer wavelength)

Front 42

How did Bohrs model fail?

Back 42

-failed to predict emisson spectra of other elements that contained more than one electron

Front 43

Summarize the Bohr model

Back 43

-Electrons exist in quantized orbits at specific, fixed energies and specific, fixed distances from the nucleus

Front 44

Summarize the Bohr model

Back 44

When energy is put into an atom, electrons are excited to higher-energy orbits

Front 45

Summarize the Bohr model

Back 45

when electrons fall from higher energy to lower energy orbits (relax) atoms emit light

Atoms emit light during the reconfiguration relaxation period following excitation

Front 46

Summarize the Bohr model

Back 46

The energy (and therefore the wavelength) of the emitted light corresponds to the difference in energy between the two orbits in the transition. Since these energies are fixed and discrete, the energy (and therefore the wavelength ) of the emitted light is fixed and discrete

Front 47

compare the following electrion orbit transitions

n = 3 --> n = 2

to

n = 2 --> n = 1

Back 47

the second transition will have a higher energy output; larger energy per photon; higher freq and shorter wave length

this is becase the distance between orbits closer to the nucleus are much greater than on the peripheral therfore more energy is released when the electrons relaxes to a lower energy orbit

Front 48

Bohr Model vs Quantum - Mechanical Model

Back 48

Orbits vs Orbitals

specific paths vs. probability maps

Front 49

Revolutionary Concept introduced about the electron in the quantum model

Back 49

-electrons do not behave like particles

-no fixed paths

-obrital represents not how electron moves but the probability of where the electron may be found

Front 50

Bohr Model vs Quantum - Mechanical Model

Back 50

Orbits vs Orbitals

specific paths vs. probability maps

Front 51

Revolutionary Concept introduced about the electron in the quantum model

Back 51

-electrons do not behave like particles

-no fixed paths

-obrital represents not how electron moves but the probability of where the electron may be found

Front 52

Wave - Particle Duality

Back 52

Like photons sometimes electrons act like particles other times like waves

impossible to trace is path

only predict probability

Front 53

Bohr model vs Quatumn model

Back 53

orbits with different radii vs orbitals with different shapes

Front 54

Wave - Particle Duality

Back 54

Like photons sometimes electrons act like particles other times like waves

impossible to trace is path

only predict probability

Front 55

Bohr model vs Quatumn model

Back 55

orbits with different radii vs orbitals with different shapes

Front 56

Orbitals

Back 56

-Lowest energy orbital is 1s

Front 57

Orbitals

Back 57

-Lowest energy orbital is 1s

Front 58

What does the number represent in the orbital

Back 58

- called the principal quantum number and specifies principle shell

-higher principal quantum number higher the energy of the orbital

Front 59

What does the letter indicates

Back 59

the subshell of the orbital and specifies its shape

Front 60

Possible subshell letters

Back 60

s,p,d, f

Front 61

S Subshell orbital shape

Back 61

Spherical

Front 62

1s orbital analogy using dots

Back 62

density of dots larger around nucleus

Front 63

1s orbital

Back 63

spherical representation because of symmetical distribution around nucleus

Front 64

Ground state

Back 64

Lowest energy state; single electron of hydrogen in 1s orbital

Front 65

Principal quantum number 2

Back 65

- the 2 principal shell contains to subshells s and p

Front 66

Relationship between Shell number and subshell amount

Back 66

The number of subshells in a given principal shell is equal to the value of n

Front 67

Electron Configuration

Back 67

-shows the occupation of orbitals by electrons for a particular atom

Front 68

Pauli Exclusion Principle

Back 68

-the orbitals may hold no more than two electrons with opposing spins

Front 69

Electron Spin

Back 69

fundamental property of electrons

Front 70

Ordering Electrons

Back 70

-different subshells within the same principal shell have different energies

-energy ordering is not determined by quantum number alone

-4s is lower than 3d electrons will fill 4s shell before 3d shell

Front 71

Learning check Electron Configurations part 1

Back 71

-electrons occupy orbitals so as to minimize the energy of the atom; therefore, lower-energy orbitals fill before higher-energy orbitals.

- each orbital hold no more than two electrons with opposing spins (Pauli exclusion principle)

-Hund's Rule electrons fill in singly before pairing