This model was developed after J.J. Thompson discovered electrons, a particle smaller than an atom. It shows electrons floating freely in a positive region.

In the gold foil experiment, most of the positively charged alpha particles passed through the gold foil, but some were deflected or bounced back.  What did we conclude because of this?  

Which scientist is responsible for first stating that all the atoms of a particular element are identical but are different from the atoms of all other elements?

Confidence with the last lesson.

An atom is electrically neutral because

What is atomic number?

What electrical charge does a proton have?

What mass does a neutron have?

How many electrons does a sodium atom have?

The __________ of an atom is the sum of the protons and neutrons in the nucleus of that atom.

The mass number of an element that has 18 protons, 18 electrons, and 19 neutrons is _____.

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