Periodic Table Study Guide How to Draw Bohr Diagrams

CHEM Bohr ’ s Explanation Light can have only discrete amounts of energy – Energy is quantized Electron can have only these energy values and no others

CHEM Bohr Model Postulated That electrons occupy specific orbits – Similar to planets orbiting sun -- -

CHEM Bohr Atom details Each Shell can hold a certain number of electrons – Given by #of electrons in shell = 2n 2 - First shell (orbit) #of e - = 2(1) 2 = 2 e - Second shell (orbit) #of e - = 2(2) 2 = 8 e - Third shell (orbit) #of e - = 2(3) 2 = 18 e -

CHEM Bohr Atom details Each Orbit has a specific energy level - First shell (orbit) Lowest energy level Second shell (orbit) Higher energy level Third shell (orbit) Higher energy level

CHEM Transitions Between Orbits Each Orbit has a specific energy level - Must add the right amount of energy to transition between energy levels E=hv A particular color of light has the right amount of energy -

CHEM Transitions Between Orbits Going from higher energy to lower energy orbits a Photon is emitted - -

CHEM Ground and Excited States Electrons “ prefer ” to be in the lowest energy level – levels closest to the nucleus – Ground state Excited state – electron goes from the lowest energy level to a higher energy level

CHEM Ground State/Excited State - n=1 energy level n=2 energy level n=3 energy level - Hydrogen example Ground State All electrons in lowest possible energy levels Excited State at least one electron promoted to a higher energy levels -

CHEM Ground State/Excited State - n=1 energy level n=2 energy level n=3 energy level - Lithium example Z = 3 Ground State Excited State

CHEM Bohr Atom Usefullness Bohr atom model worked very well for Hydrogen but did not agree with experiment for heavier elements Hydrogen Bohr Atom Model worked well Other Elements Bohr Atom Model did not accurately predict energy levels Bohr was on the right track but hypothesis needed more work

What are the results?

Bohr Diagrams 1)Find your element on the periodic table. 2)Determine the number of electrons – it is the same as the atomic number. 3)This is how many electrons you will draw.

Bohr Diagrams Find out which period (row) your element is in. Elements in the 1 st period have one energy level. Elements in the 2 nd period have two energy levels, and so on.

Guided Practice Protons: _____Neutrons: _____Electrons: ______ How many energy shells will this have? ____ How many valence (outer) electrons does this element have? ____ Bohr Model: 11 Na Sodium

Bohr Diagrams C C 1)Draw a nucleus with the element symbol inside. 2)Carbon is in the 2 nd period, so it has two energy levels, or shells. 3)Draw the shells around the nucleus.

Bohr Diagrams 1)Add the electrons. 2)Carbon has 6 electrons. 3)The first shell can only hold 2 electrons. C C

Bohr Diagrams 1)Since you have 2 electrons already drawn, you need to add 4 more. 2)These go in the 2 nd shell. 3)Add one at a time - starting on the right side and going counter clock-wise. C C

Bohr Diagrams 1)Check your work. 2)You should have 6 total electrons for Carbon. 3)Only two electrons can fit in the 1 st shell. 4)The 2 nd shell can hold up to 8 electrons. 5)The 3 rd shell can hold 18, but the elements in the first few periods only use 8 electrons. C C

Bohr Diagrams Try the following elements on your own: a)H b)He c)O d)Al e)Ne f)K C C

Bohr Diagrams Try the following elements on your own: a)H – 1 electron b)He c)O d)Al e)Ne f)K H H

Bohr Diagrams Try the following elements on your own: a)H b)He - 2 electrons c)O d)Al e)Ne f)K He

Bohr Diagrams Try the following elements on your own: a)H b)He c)O - 8 electrons d)Al e)Ne f)K O O

Bohr Diagrams Try the following elements on your own: a)H b)He c)O d)Al - 13 electrons e)Ne f)K Al

Bohr Diagrams Try the following elements on your own: a)H b)He c)O d)Al e)Ne - 10 electrons f)K Ne

Bohr Diagrams Try the following elements on your own: a)H b)He c)O d)Al e)Ne f)K - 19 electrons K K

Guided Practice Protons: _____Neutrons: _____Electrons: ______ How many energy shells will this have? ____ How many valence (outer) electrons does this element have? ____ Bohr Model: 3 Li Lithium

Guided Practice Protons: _____Neutrons: _____Electrons: ______ How many energy shells will this have? ____ How many valence (outer) electrons does this element have? ____ Bohr Model: 15 P Phosphorus

Guided Practice 16 S Sulfur Protons: _____Neutrons: _____Electrons: ______ How many energy shells will this have? ____ How many valence (outer) electrons does this element have? ____ Bohr Model:

Bohr Diagrams End of Study Guide. You should know how to draw a Bohr Diagram for the first 20 elements.