1. Chapter 4 – Atomic Structure
4. 1-2

2. 4.1 Defining the Atom
What is an atom? How can we define, study, and believe in something we can’t see?

3. An Atom is the smallest particle of an element that retains its identity in a chemical reaction.
We will study the atom by looking at the evolution of the understanding of the atom. Noting both the accurate and inaccurate ideas are both important.
This is Key

4. Democritus’s Atomic Theory (460 B.C. -370 B.C.)
Atoms are indivisible and indestructible

5. Dalton’s Atomic Theory
1. All elements are composed
of tiny indivisible particles
called atoms.
2. Atoms of the same element are identical. Atoms of one element are different from those of all other elements.

6. Dalton’s Atomic Theory
3. Atoms of different elements can physically mix or chemically combine in simple whole number ratios to form compounds
4. Chemical reactions occur when atoms are separated, joined, or rearranged. However, Atoms of one element can not be changed into an atom of another element.

7. Sizing up the Atom
How small are we talking about? Let’s consider this copper (Cu) penny. How many atoms line up end to end in 1 cm?

8. Sizing up the Atom 100,000,000 copper atoms lined
up end to end is about 1 cm.
There are 2.4 x 1022 Cu atoms
in a single penny
There are 6 x 109 people
on the planet Earth

9. How can we see an atom?
Scanning Tunneling Microscopes Field Electron Emitting Microscopes

10. 4.2 Structure of the Nuclear Atom
Subatomic Particles
Electrons
Protons
Neutrons

11. Electrons
Thomson (1856 – 1940)
Negative Plate
Positive Plate

12. Electrons Thomson (1856 – 1940) What does this tell us about the atom?
Negative Plate
What does this tell us about the atom?
Positive Plate

13. Electrons
Electrons are negatively charged subatomic particles.

14. Properties of Subatomic Particles
Relative Relative Particle Symbol Charge Mass Electron e- 1- 1/1840 Proton p Neutron n0 0 1

15. The Atomic Nucleus
Rutherford’s Gold Foil Experiment (1911)

16. The Atomic Nucleus Rutherford’s Gold Foil Experiment (1911)
What does this tell us about the atom?

17. The Atomic Nucleus The nucleus is a relatively tiny core of the atom
Contains Protons and Neutrons
Makes up most of the mass and density of the atom
This means that most of the volume is occupied by the electrons