1. Bohr’s Model of Electron Arrangement

2. Atomic Structure Atomic number = the number of protons
Atoms are neutral, so the number of protons = the number of electrons
Atomic mass ≈ the number of protons + the number of neutrons
Protons and neutrons have the same mass, which is 1800 times bigger than the mass of electrons.

3. Element Symbol Atomic Mass Atomic Number # of Protons # of Neutrons
Examples:
Element
Symbol
Atomic Mass
Atomic Number
# of Protons
# of Neutrons
Oxygen O 16 8
Lithium Li 7 3 4

4. Bohr Model
1913 – Bohr explains movement of electrons around the nucleus of the atom.
Bohr’s model:
Electrons orbit around the nucleus
Each orbit is a certain distance from the nucleus
Each orbit has a definite energy level
Each orbit has a definite number of electrons
1st orbit 2
2nd orbit 8
3rd orbit 8

5. 7 15 Examples: Valence Shell – the outer shell of electrons
Valence electrons – the electrons in the outer shell of an atom
Valence – the number of electrons in the outer shell of an atom
Name
Symbol
Electrons
Bohr Diagram
Nitrogen
Phosphorus 7 15

6. Do Bohr Diagrams of
first 20 elements/atoms

7. Bohr Models and the Periodic Table
Most elements in the same family have the same number of valence electrons (an exception is Helium)
Elements in the same period have valence electrons in the same shell.
The period number indicated the number of shells that have electrons.
The number of electrons in a shell corresponds to the number of elements in that period.

8. Valence shells and Stability
Atoms become stable when they have a full outer shell of electrons
Noble gases are un-reactive because they have a full outer shell of electrons.
Atoms in other families will gain or lose electrons to have a full outer shell.

9. Having an uneven number of protons and electrons gives an atom a charge.
Charged atoms are called ions.
Atoms  protons = electrons
Ions  protons ≠ electrons
Metals lose electrons to become positive ions.
Non-metals gain electrons to become negative ions.
Atom
Ion
3 electrons and 3 protons
2 electrons and 3 protons

10. The charge of an ion is equal to the sum of the charges of the protons and electrons.
Ions are written as the chemical symbol with a superscript of their charge

11. 18 2+ 12 10 Bohr Models of Ions 16 Ion Atomic Number # of Protons
# of Electrons
Bohr Model
Sulphur Ion
Ion Charge: 2- 16 18
Magnesium
Ion Charge 2+ 12 10

12. Do Bohr Diagrams of
first 20 ions