2.2 Electrons in Atoms Niels Bohr (1885-1962) – proposed the ‘planetary model’. Electrons have...

2.2 Electrons in Atoms

•Niels Bohr (1885-1962) – proposed the ‘planetary model’.

•Electrons have energy of motion.

•Electrons absorb energy and move to higher energy states.

•Electrons give off that energy in the form of light when they fall back down to lower energy states.

2.2 Electrons in Atoms

Electrons are the parts of an atom that are lost, gained or shared when an atom reacts.Electrons and their arrangement in the atom determine an element’s chemical properties and behavior. The Modern Electron Cloud Model of the atom – Describes the current understanding of Atomic Structure.Electrons occupy orbits of only certain amount of energy.Energy levels are spherical regions (3D) where there is a high probability of finding an electron.

Relationship of Light (energy) and Atomic Structure:

Electromagnetic Spectrum – Range of Wavelengths

•ALL Electromagnetic Waves travel at the speed of light = 300 million meters per second or (3.0 x 10 8 m/s)

•Two main properties of electromagnetic waves are the wavelength and the frequency of the wave.

•The wavelength is the distance between two peaks or troughs.

•Units: meters or nm (10 -9) of a meter or one billionth of a meter.

Formula: C = λ f

C = speed of light, λ (lambda) = wavelength and f = the frequency.

•The frequency is the number of vibrations per second. Units are given in Hertz (Hz)

•Wavelength is inversely proportional to frequency

•Increase wavelength , decrease frequency

•Decrease wavelength , increase frequency

Electrons and Light

•When atoms are energized by an electric current they emit light.

•When this light is passed through a prism they produce an emission spectrum.

When ‘white’ light is passed through a prism you can see all the colors of the rainbow. “Continuous Spectrum”

The spectral lines emitted from excited atoms when they fall back to a stable state is called an emission spectrum.

Each element has its own unique atomic emission spectrum. Fingerprint

http://phys.educ.ksu.edu/vqm/html/emission.html

When the exited electron fall back to a stable state they only release the amount of energy they absorbed and therefore only release certain frequencies of light.

•The electrons in the outermost energy level are called – valence electrons.

•Chemical and physical properties are directly related to valence electrons.

•Lowest energy level can only hold up to 2 electrons

•The second energy level can hold up to 8 electrons.

•The third energy level can hold up to 18 electrons.

The electrons in the outermost energy level are called – valence electrons.Chemical and physical properties are directly related to valence electrons. Lowest energy level can only hold up to 2 electronsThe second energy level can hold up to 8 electrons.The third energy level can hold up to 18 electrons.

The Periodic Table can be used to predict valence electrons.

•All atoms in group 1 have 1 valence electron

•All atoms in group 2 have 2 valence electrons

• All atoms in group 13 have 3

•All atoms in group 14 have 4 ect.

Group 18 – 8 Valence electrons Exception: helium – only 2 valence electrons

Lewis Dot Diagrams - models that show valence electrons

Each ‘dot’ represents one valence electron

HElectron Dot Diagram for Hydrogen

One valence electron – it only has one!

Cl

Electron Dot Diagram for Chlorine

Chlorine – group 17 – 7 valence electrons

Topic 2Topic 2

Basic Concept QuestionsBasic Concept Questions

A. Chlorine

Write a Lewis dot diagram for each of the following.

Question 2

C. Potassium

B. Calcium

A. Chlorine

Answer

C. Potassium

B. Calcium

Topic 2Topic 2

Basic Concept QuestionsBasic Concept Questions