1. The Atom

2. Everything is made of atoms.
Atoms are the smallest part of matter.
Atoms are made of 3 subatomic particles: electrons, protons, and neutrons.

4. Nucleus Center of the atom Contains protons and neutrons
Contains almost all of the mass of the atom

5. Our modern model of the atom comes from the contributions of several scientist over millennia.

6. Democritus (BC 460-370) Greek scientist
proposed that there had to be a smallest part of matter, which he called atomos (indivisible)
Indivisible atoms are hard spheres.

7. John Dalton 1808
Published a theory of the atom that had these important points:
All atoms of a particular element are the same.
Atoms of different elements have different
properties, mass, and chemical reactivity.
Atoms are not changed by chemical reactions, just rearranged in order or number.

8. J.J. Thomson 1897 Discovered electrons
Knowing atoms were neutral, he thought that electrons were like negative plums in positive pudding.
Plum pudding model:

9. Ernest Rutherford 1911 Discovered the nucleus
shot alpha particles at gold foil, most but not all passed through – some were bounced back (positive nucleus)
the atom is mostly empty space with a
solid, central nucleus

10. Niels Bohr 1913
while studying light, realized that electrons can only exist in certain energy levels or orbitals

11. Modern Day
Scientists have now split the atom and even split protons, neutrons, and electrons into even smaller particles called quarks.

12. Subatomic Particles “smaller than the atom”.
Each particle has different properties and locations.

13. Protons Positively charged particles Located in the nucleus
Determine what element as atom is

14. Neutrons Neutral particles Located in the nucleus
Gives mass but no charge to the atom
Determines the isotope

15. Electrons Negatively charged particles Located outside of the nucleus
Can be lost or gained to and from other atoms
Very small mass; 1/2000th of a proton
Determines the ion

16. An atom is a single piece of an element that retains the element’s properties.

17. All elements are found on the periodic table of elements.
An element has only
one kind of atom.
All elements are found on the periodic table of elements.

18. A molecule is any
combination of two or
more atoms.
Not all molecules are compound.

19. A compound is any
combination of two or more different atoms.

24. Beginning to Read the Periodic Table

26. Changes in Atoms Isotopes Ions When an atom loses or gains neutrons
Everything else stays the same
When at atom loses or gains an electron
The atom becomes electrically charged