Read and ExplainChapter 5 Electrons in atoms

5.1 Models of the atom

The Bohr Model

•Niels Bohr (1885 – 1962)

•Proposed the electron is found only in specific orbits around the nucleus

•The orbits are in specific energy levels

•Electrons can jump from one level to the next. The higher the energy level takes more energy but not an even energy jump at the higher energy levels

Energy levels

•Energy levels are the specific levels where the electrons can be found.

•Closer to the nucleus the lower energy level.

•With the input of energy the electrons can move to higher energy levels

•When falling back to lower energy levels light is emitted.

Quantum of energy

•The amount of energy required to move an electron from one energy level to the next.

Quantum Mechanical Model

•Proposed by Erwin Schrodinger (1887 - 1961)

•Using mathematical equations supported the idea there are allowed energies an electron can have and how likely it is to be found in various locations around the nucleus.

•QMM – has areas where the electron is more likely to appear but can not specifically determine where it will be at any given time

Atomic orbital

•The equation developed by Schrodinger give the energies an electron can have (energy levels)

•Each energy level corresponds to an atomic orbital

•The orbital is a defined region in space and has different shapes depending on principal quantum level

Principal quantum numbers

•The energy levels in QMM are labeled by principle quantum numbers (n)

•Each quantum level has sub levels. The number and type depend on the quantum level.

•Levels go from 1 – 7 and follow the periods on the periodic table

Energy sublevels (s, p, d, f)

•The 1st quantum level has only a “s” sublevel

•2nd quantum level has s and p sublevels

•3rd QL has s, p, d sublevels

•4th and higher QL have all sublevels

sublevel

•Are sublevels of a quantum level (n)•Sublevels have specific shape orbitals•Consist of s, p, d, f•s – 1 orbital•p – 3 orbitals•d – 5 orbitals• f – 7 orbitals

P sublevel

•P sublevel found in each quantum level 2nd and above.

•Higher in energy than the s orbital

•Three orbital orientations of the dumbell shaped orbitals – follow the x, y, z planes

D sublevel

•First found in the 3rd quantum level

•5 orientations

F sublevel

•First found in the 6 period 4th quantum level

•Has 7 orbitals

Electron configurations

•The way the electrons are arranged in the various orbitals around the nucleus

5.2 Electron Arrangement in Atoms

Electron configurations

•The way the electrons are arranged in various orbitals around the nucleus.

•Electrons are arranged to form the most stable arrangement

Aufbau principle

•One of three principles that applies to electron configurations

•Electrons occupy the orbitals of the lowest energy first

Pauli exclusion principle

•An atomic orbital can have at most two electrons

•When two electrons are in an orbital then they have a spin in opposite directions

Hund’s rule

•Electrons occupy orbitals of the same energy in a way that makes the electrons spin with the same direction until all the orbitals have at least one electron in them.

5.3 Physics and the Quantum Mechanical Model

amplitude

•QMM grew out from study of light

•Light consists of waves

•One of the properties of waves is amplitude

•Amplitude is wave height from zero to the crest

Wavelength

•Represented by the greek symbol lambda

• Is the distance between wave crests

frequency

•Represented by Greek symbol v (nu)

• Is a measure of the number of crests passing a fixed point in a unit of time.

•Usually in cycles per second

hertz

•The SI unit of cycles per second or hertz

•Represented by symbol (s-1)

Wave speed formula

•The equation for speed of light

•c = lambda x nu

Electromagnetic radiation

•Light is part of the electromagnetic spectrum

• Includes radio waves, microwaves, infrared waves, visible light, ultraviolet waves, X-rays, gamma rays

•Wavelengths from 1 x 102 m to 1 x 10-14 m

•Radio waves longest, gamma rays shortest

•Frequency inversely proportional to wavelength

Atomic emission spectrum

•When atoms absorb energy moving electrons to higher energy levels

•When electron returns to lower energy level light is emitted

•Light emitted by an element separate into discrete lines that are the elements atomic emission spectrum

photons

•A discrete bundle (quanta) of electromagnetic energy•They are always in motion and travel at the speed of light in a vacuum •They have zero mass and rest energy•They carry energy and momentum (momentum is mass x velocity)•Have particle-like interactions (think billiard balls colliding)