# The ATOMPage 2

#### WATCH ALL SLIDES

He received the Nobel Prize in physics in 1922 for his theory.

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## Quantum Mechanics Model

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Quantum Mechanics Model

Electron Cloud Model (1920's)

an atom consists of a dense nucleus composed of protons and neutrons surrounded by electrons that exist in different clouds at the various energy levels.

Erwin Schrodinger and Werner Heisenburg developed probability functions to determine the regions or clouds in which electrons would most likely be found.

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A combination of all models…

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## Drawing Bohr Diagrams

Atomic number:

identifies the element

equal to the number of protons in the nucleus

since atoms are electrically neutral, # of protons = # of electrons

Mass number:

# of protons + # of neutrons

# neutrons = atomic mass (rounded off) – atomic #

Protons and neutrons account for most of the mass of the atom

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Bohr Diagrams (continued)

an energy level represents a specific value of energy of an electron and corresponds to a general location around the nucleus

the number of occupied energy levels in any atom is normally the same as the period number in which an atom appears

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for the first 3 energy levels, the maximum number of electrons that can be present are 2, 8 and 8 in order of increasing energy (increasing distance from the nucleus)

a lower energy level is filled with electrons to its maximum level before the next level is started.

The electrons in the highest (outermost) occupied energy level are called valence electrons. Number of valence electrons is the same as the group number for group A elements (1,2,13-18).

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Bohr Diagrams (continued)

Draw a circle for the nucleus

Put in the number of protons and neutrons inside the circle.

Determine the number of electrons and place them in energy levels starting closest to the nucleus and filling them in the order of 2, 8, 8.

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## Stable Atoms

have low chemical reactivity

include noble gases, all of which have 8 valence electrons (except He, which has 2)

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