1. ATOMS AND ATOMIC STRUCTURE Atom Nucleus Proton Neutron Electron

2. The smallest unit of an element.
WHAT IS AN ATOM?
The smallest unit of an element.
Consists of a central nucleus surrounded by one or more electrons.

3. The central part of an atom. Composed of protons and neutrons.
WHAT IS THE NUCLEUS?
The central part of an atom.
Composed of protons and neutrons.
Contains most of an atom's mass.

4. Positively charged particle.
WHAT IS A PROTON?
Positively charged particle.
Found within an atomic nucleus.

5. Found within an atomic nucleus.
WHAT IS A NEUTRON?
Uncharged particle.
Found within an atomic nucleus.

6. Negatively charged particle.
WHAT IS AN ELECTRON?
Negatively charged particle.
Located in shells that surround an atom's nucleus.

7. Electron Cloud !!!

8. Electron Cloud: A space in which electrons are likely to be found.
Electrons whirl and revolving about the nucleus billions of times in one second
Location of electrons depends upon how much energy the electron has.

9. Electron Cloud:
Electrons with the lowest energy are found in the energy level closest to the nucleus
Electrons with the highest energy are found in the outermost energy levels, farther from the nucleus.

10. Bohr Model
In 1913, the Danish scientist Niels Bohr proposed his model, he placed each electron in a specific energy level.

11. Bohr Model
According to Bohr’s atomic model, electrons move in definite orbits around the nucleus, much like planets circle the sun. These orbits, or energy levels, are located at certain distances from the nucleus.

12. Atomic Structure

13. Atomic Number = number of protons
Describing Atoms
Atomic Number = number of protons
In a neutral atom, the # of protons = the # of electrons
Atomic Mass= the number of protons + the number of neutrons

14. Isotopes The number of protons for a given atom never changes.
The number of neutrons can change. 
Two atoms with different numbers of neutrons are called isotopes
Isotopes have the same atomic #
Isotopes have different atomic Mass #’s

15. Isotopes

16. Ions An atom that carries an electrical charge is called an ion
If the atom loses electrons, the atom becomes positively charged (because the number of positively charged protons will be more the number of electrons)
If the atom gains electrons, the atom becomes negatively charged (because there are more negative charges than positive)

17. Ions The number of protons does not change in an ion.
The number of neutrons does not change in an ion.
So, both the atomic number and the atomic mass remain the same.

18. Ions
This atom has lost an electron. Now it has one more proton than electron.
One more proton means one more positive charge.
This makes the total charge of the atom POSITIVE.
This atom has gained an electron. Now it has one less proton than electron.
One less proton means one less positive charge.
This makes the total charge of the atom NEGATIVE.