What is an atom???

An atom is the smallest particle of an element that retains its identity in a chemical reaction.

What are the parts of the atom???

1.) Protons

2.) Neutrons

3.) Electrons

Positively charged!!

Neutral

Negatively charged

What information do we get about an atom from the

Periodic Table of Elements?Mass number= # of protons

+# of neutrons

Atomic number= # of protons

(ID # of an element)

# of protons= # of electrons

Electron configurationHow many electrons can

you count??

# of protons= # of electrons

Where are protons, neutrons, & electrons located in an

atom?• John Dalton’s Model of the Atom:

Atoms are tiny, indestructible

particles, with no internal structure.

• J. J. Thomson’s Model of the Atom:

Plum Pudding Model

• Ernest Rutherford’s Model of the Atom:

Rutherford’s Gold Foil Experiment

Ernest Rutherford’s Model of the Atom:

The nucleus is the tiny, central core of the atom…contains protons & neutrons

The electrons are distributed around

the nucleus and occupy most of

the volume of the atom.

• Niels Bohr’s Model of the Atom:

Planetary Model of the Atom

Electrons move in

circular orbits at fixed

distances from the nucleus.

Given: Mass # = 43 # of electrons = 21

a.) How many protons does this atom have?# protons = # of electrons

b.) What is the identity of this atom?# of protons = atomic #

c.) How many neutrons does this atom have?mass # = # protons + # neutrons