Atoms Exist!
• Since Dalton’s time, many experiments have been performed to prove that atoms are real
Neils Bohr
Ernest Rutherford
• So what is an atom?
J.J. Thomson
Robert Brown
Albert Einstein
James Chadwick

• Grind gold ring down into a pile of gold dust
• Is the gold dust still gold?

Atom
• the smallest particle of an element that retains the properties of the element

SIZE
How BIG is small?

Copper atom diameter
1.28 x 10⁻¹⁰ m
Cu

Size
• If an atom were the size of an orange, a real orange would be the size of the Earth

Scanning Tunneling Microscope
• Too small to be seen with visible light.
Use a STM to form a picture of them
Silicon atoms

How STMs work
We don’t directly see them, but the tip feels the electrons of each atom and makes an image of what the atoms look like

Taking it to the next level…
• Manipulate atoms to form shapes
World’s smallest writing
Silicon and Tin atoms

Subatomic Particles:
• Electrons, Protons, and Neutrons
Dalton’s Atom

• Small, dense region in the center of the atom; made of protons and neutrons
• Makes up 99.97% of the atom’s mass

• large outer region of the atom where electrons orbit around the nucleus

Electron Cloud
• Makes up most of the atom’s volume
• Held in place because of attraction to positively charged nucleus

The atom is made of mostly empty space
Who came up with that idea?

If an atom were two football fields in diameter, the nucleus would be the size of a nickel

If matter is mostly empty space, what keeps us from oozing through things?

Particle
Electron
Symbol
Electrons
Location Charge Relative Mass e⁻ Surrounds nucleus
-1 1/1840

Particle
Proton
Symbol
Protons
Location Charge Relative Mass p In nucleus +1 1

Particle
Neutron
Symbol
Neutrons
Location Charge Relative Mass n In nucleus 0 1

Particle
Electron
Take a Look…
Symbol Location Charge Relative Mass
1/1840
Proton
Neutron p n e⁻ Surrounds nucleus
In nucleus
-1
+1
In nucleus 0
1
1

Question?
• The mass of a atom comes mostly from its
_______________.
• The volume of an atom comes mostly from its
_________________.