1. Give the symbol and number of protons in one atom of:
Barium
Selenium
Sulfur
Give the symbol and number of electrons in a neutral atom of:
Beryllium
Tungsten
Arsenic
Give the symbol and number of neutrons in one atom of:
Boron
Xenon
Lead

2. Modern Atomic Theory

3. Bohr’s Model of the Atom
Bohr described the arrangement of electrons in each atom.
Looks like a solar system with planet revolving around the sun.
Bohr’s model is the basis for modern atomic theory.

4. Energy Levels
In Bohr’s model, electrons move with constant speed in fixed orbits around the nucleus.
Each electron has a specific amount of energy.
The possible energies that an electron can have in an atom are energy levels.

5. How Do Energy Levels Work?
Energy levels are like staircases.
The higher you are the more energy you have.
You can only travel in whole step increments.
high energy
low energy

6. An electron in an atom can move from one energy level to another when the atom gains or loses energy.
The size of the jump between energy levels determines the amount of energy gained or lost.

7. How to Draw a Bohr Diagram (in our class anyway)
Place the chemical symbol in the middle with a circle around it.
Place the number of electrons in orbits around the nucleus by drawing circles around the nucleus. 1st shell – 2 electrons
2nd shell – 8 electrons,
3rd shell – 8 electrons

8. How to Draw a Lewis Dot Structure (again in our class!)
Count the number of valence electrons
Valence electrons are only those in the outermost shell!
Put chemical symbol in the middle and draw valence electrons around the symbol. Start at the top for the first 2 electrons and then go clockwise around.

9. Electron Cloud Model
Bohr’s model was somewhat correct, but scientists now know that electrons move in a less predictable way.
An “electron cloud” is a visual model of the most likely locations for electrons in an atom.

10. An electron cloud represents all the orbitals in an atom.
Scientists use the electron cloud model to describe the possible locations of electrons around the nucleus.
An electron cloud represents all the orbitals in an atom.
An orbital is a region of space around the nucleus where an electron is likely to be found.
Think about your most likely spots to be found and you can create your own orbital!

12. How Many Orbitals Are In Each Energy Level?
Number of Orbitals
Maximum Number of Electrons

14. Electron Movement for Different Atoms
Hydrogen
Nitrogen-7
Carbon-6
Oxygen-8

15. Electron Configurations
Arrangement of electrons in the orbitals of an atom.
Ground State:
The most stable electron configuration is the one in which the electrons are in orbitals with the lowest possible energies.
Excited State:
If energy is absorbed and the electrons jump to a higher energy level, the atom is in a less stable state.

17. How do Fireworks… Work?
Heat produced by explosion causes some electrons to move to a higher energy level.
When the electrons move back to lower energy levels they give off energy.
This energy can be given off in the form of light.
There are different colors because different elements emit different colors of light.

18. The Atom