Periodic Law of the Elements
when elements are arranged in a particular order (increasing atomic number), elements of similar properties occur at periodic intervals
The Theoretical basis for the periodic law lies in
electronic theory
A new set of physical laws were needed to explain what experiments were revealing about atoms and light
- These laws predicted quantized (non-continuous) behavior
- These laws lead to strange predictions of behavior that is impossible to picture, but explains countless experiments
- Our objective is to understand how electrons behave in the atom
The energy of an electron in an atom is quantized
it exists only in certain fixed quantities, rather than being continuous
It is physically impossible to determine a quantum particle’s
position and momentum
Light
- is a form of electromagnetic radiation
- travels as waves at a constant speed
- carries radiant energy through completely empty space
All waves have:
Wavelength and Frequency
Wavelength
horizontal distance between two corresponding points on a wave (units are usually m)
Frequency
the number of complete wavelengths that pass a stationary point in a second (units are usually Hz, s-1)
Light is a stream of small particles called photons that have
Energy related to their frequency.
The electromagnetic spectrum
- Arranges forms of energy from lower to higher
- Arranges energy from longer to shorter wavelengths
- Shows visible light with wavelengths from 700-400 nm
All electromagnetic radiation moves through a vacuum at a specific speed.
c = 3.00 x 10^8 m/s
White light that passes
through a prism
- Is separated into all colors called a continuous spectrum
* Gives the colors of a rainbow
An atomic spectrum consists of lines
Of different colors formed when light from a heated element containing an element passes through a prism
When gases are heated, they give off light at certain frequencies
In other words, atoms absorb or emit energy only at specific wavelengths (specific energies)
Bohr’s Model of the Atom
- His goal was to create a model that would explain the atomic spectrum of Hydrogen
- Postulates that there are only certain positions about the nucleus an electron can reside – certain “allowed orbitals.”
When electrons absorb energy (in the form of light),
they move from a lower energy level to a higher one.
When electrons move from a higher energy level to a lower energy level
they give off energy in the form of light (“emission”)
Electrons are arranged in
specific energy levels that
- Are labeled n = 1, n = 2, n = 3, and so on
- Increase in energy as n increases
- Have the electrons with the lowest energy in the first energy level (n=1) closest to the nucleus
Energy Level Changes
- An electron absorbs energy to “jump” to a higher energy level.
- When an electron falls to a lower energy level, energy is emitted.
- In the visible range, the emitted energy appears as a color.
Sublevels
- The s sublevel has the lowest energy within that sublevel.
* The s sublevel is followed by the p, d, and f sublevels in order of increasing energy.
An orbital
- Is a three-dimensional space around a nucleus where an electron is found most of the time.
- Has a shape that represents electron density (not a path the electron follows).
- Can hold up to 2 electrons.
- Contains two electrons that must spin in opposite directions.
There are a different number of orbitals for each subshell type
- In an s subshell, there is 1 orbital
- In a p subshell, there are 3 orbitals
- In a d subshell, there are 5 orbitals
- In a f subshell, there are 7 orbitals.
An s orbital
- Has a spherical shape around the nucleus.
- Increases in size around the nucleus as the energy level n value increases.
- Is a single orbital found in each s sublevel.
