Chemistry Test #5

Rutherford’s Model of Atom

Could not explain chemical properties of atoms. By studying light emitted by elements, reasons for behavior became apparent.

Bohr’s Model

Electrons orbit the nucleus in shells. Electrons can be bumped up to a higher energy level if hit by an electron or a photon of light.

Line and Continuous spectra

When electrons fall back down they release a photon. These jumps down from shell to shell account for the line spectrum seen in gas discharge tubes (through spectroscopes).

Emission and Absorption Spectra

Created when electromagnetic radiation passes through a prism or grating. The emission spectrum is created when a substance emits radiation, while the absorption spectrum is created when a substance absorbs radiation. The absorption spectrum is considered the photographic negative of the emission spectrum.

ROY G BIV

Red(longest wavelength), orange, yellow, green, blue, indigo, violet(shortest wavelength)

Studying Bohr’s Model

Neils Bohr studied hydrogen atom

Proposed that electrons are found only in specific circular paths or orbitals around the nucleus.

Each possible electron orbit in Bohr’s model has a fixed energy(energy level)

energy levels get closer as you move farther from the nucleus

energy levels get higher in energy as you move farther from the nucleus

When are atoms most stable

When they have 8 electrons on their outermost shell.

What is a quantum of energy

The amount of energy required to move an electron from one energy level to another

Excited state and ground state

Excited state: When electrons gain energy and jump to a higher energy level

Ground state: Electrons lose energy and fall to the lowest energy level possible

Bohr’s Model Restrictions

Accurately describes the movement of an electron in the hydrogen atom but cannot apply to multi-electon atoms

Quantum mechanical Model of the Atom

Based on mathematical probability of the location of electrons using the schrodinger equation.

Still has energy levels, but exact path or orbit of electron in unknown

The orbitals are normally shaded with a fuzzy edge since it’s based on the probability of finding an electron.

De Broglie

Proposed the idea that electrons behave as waves.

His equation predicted that all moving particles have wavelike characteristics.

If electrons have wave like motion and are restricted to circular orbits of fixed radius, the electron is allowed only certain possible wavelengths, frequencies, and energies.

Heisenberg Uncertainty Principle

His study was the interaction of photons and electrons

Principle states that it’s fundamentally impossible to know the velocity and position of a particle at the same time.

A photon is a particle of electromagnetic radiation with no mass that carries a quantum(certain amount) of energy.

Atomic Orbitals

An atomic orbital is a region of space in which there is a high probability of finding an electron

Within the border of an atomic orbital, there is 90% chance of finding an electron

The darker the shading of the orbital, the higher the chance of finding an electron

Energy Levels

Each energy level can be composed of multiple sublevels

Energy levels are assigned a number from 1-7 based on the period (row) on the periodic table

each sublevel can be composed of multiple orbitals

sublevels assigned a letter: s, p, d, f, or g

each orbital can hold a maximum of 2 electrons

s sublevel

1 orbital

Max 2 electrons

spherical shape

as energy level increase, size of sublevel increases but still holds 2 electrons

p sublevel

3 orbitals

max 6 electrons

dumbell or tear drop shape

Each teardrop referred to as a “lobe”

d sublevel

5 orbitals

max 10 electrons

4-leaf clover shape (4 lobes) or (2 lobes and a donut)

f sublevel

7 orbitals

max 14 electrons

Future sublevels g and h

g: 9 orbitals, max 18 electrons

h: 11 orbitals, max 22 electrons

not enough elements to fill in g or h sublevels yet

would need to have an 8th period on periodic table

Aufbau Principle

Electron configuration rule:

electrons occupy lower energy levels first

Pauli Exclusion Principle

Electron configuration rule:

orbital can hold max 2 electrons at opposite spins

Hund’s Rule

Electron configuration rule:

Electrons would rather be separated in a sublevel with multiple orbitals

Noble Gases

Group 8A

8 electrons in outermost shell

excludes helium which can only have 2 electrons

Valence electron

electrons found in the s and p orbital in the last incomplete energy level

involved in bonding

C

1s² 2s² 2s^4

How many valence electrons? What group?

6 valence electrons

Group 6A

Exceptions to the rules of electron configuration

sublevels most stable when they are full or exactly half-full

this causes electrons to jump to different sublevels to make atom more stable

This jumping does not occur until the 3rd energy level

What is most stable electron configuration of Cr

1s² 2s² 2p^6 3s² 3p^6 4s^1 3d^5←—half full

What is light composed of

photons and waves

What are the properties of light?

Crest: highest point of wave

Trough: lowest point of wave

Amplitude: Distance between rest position and crest

Wavelength (lambda): distance between 2 crests or 2 troughs

What is the speed of light

3.0 × 10^8 m/s

Calculate wavelength of yellow light emitted by a sodium lamp with a frequency of 5.10 × 10^14 Hz.

C= (wavelength)(frequency)

3.0 × 10^8 m/s= (wavelength)(5.10 × 10^14 s^-1)

=5.88 × 10^-7 m

Electromagnetic Spectrum

As electromagnetic waves travel at same speed, so as wavelength increases, frequency decreases

Gamma Rays, X-ray, ultraviolet, Infrared, microwave, radiowaves,

Visible light: ROY G BIV (400-700 nanometers)

Light is electromagnetic radiation and is characterized by its wavelength

because of its electric and magnetic properties, light is also known as electromagnetic radiation

Energy is quantized

Quantum Theory

Energy of a single quantum of energy (photon)

E=hv

E=energy (in Joules)

h= Planck’s constant 6.63 × 10^-34 J*s

Calculate energy of a photon with wavelength of 700.0 nm.

700.0 nm x (1m/ 10^9 nm)= 7.000 × 10^-7 m

C= (wavelength)(frequency)

3.00 × 10^8 m/s= (7.000 × 10^-7 m)(frequency)

E= hv

E= (6.63 × 10^-34 J*s)(4.286 × 10^4 s^-1)

E= 2.842 × 10^-29

Photoelectric Effect- Einstein

the emission of electrons when electromagnetic radiation, such as light hits material. Electrons emitted are photoelectrons.

Light shined has high enough energy on metal

Group 1A can easily exhibit this.

Grou[s 4A-8A (nonmetals) cannot due to valence electrons held so tightly

Dilemma of Photoelectric Effect

Is light a wave or particle?

Conclusion: light must have particle and wave characteristics

Atoms emit light

when heat, electricity, or reaction energy added

electrons start at ground state then absorb energy to jump to a higher energy level

have to lose energy to fall to ground levels then release the energy in the form of visible light

Atomic Emission Spectra

Atomic emission spectra is a set os specific wavelengths emitted when an element is electrified

it is unique for each element

what is n

Principle quantum number (energy level)

1s² 2s² 2p^6 3s² 3p^6 4s²

Period, block, ion form, group, short form, element?

Period: 4

Block:s

Ion form: +2

Group:2A

How many energy levels do atoms have?

7 levels (7 periods on periodic table)

Ground state or excited?

1s² 2s² 2p^6 3s² 3p^6 4s^1 6s^1

Excited state

ns² np²

group? ion prediction? valence electrons?

Valence electrons: 4

Group: 4A

Ion prediction: plus or minus 4 electrons

Know the ion formations and sublevel blocks on periodic table.

see periodic table