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How are atoms studied?
• Atoms are the building blocks of matter
• Atoms are too small in size to study easily
• Size of Earth : soda can = soda can : atom
Who studied the atom?
• Studied by many scientists for centuries
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Democritus (400 BC) – phrase “atomos”
Rutherford (1911) – nucleus (gold foil expt)
Moseley (1913) – X-rays to find atomic #
*Bohr (1913) – planetary model of the atom
*Schrödinger (1923) – electron cloud model
I’m an electron!
I’m a proton!
I’m a neutron!
I was walking along and I saw these two.
I was telling jokes to the neutron.
The proton and I were having fun.
They looked so happy there together.
I was p o s i t i v e l y charged!
I couldn’t have amassed more happiness.
The proton looked happy, so I wandered closer.
I could see the electron coming near.
The who? Huh?
They were HUGE next to me!
The electron was so cute!
Like a speck of dust, or something…
I didn’t want to seem obvious, so I kept walking.
Around and around the electron goes.
Hey electron, you’re making the proton dizzy.
The proton seems so happy with the neutron.
I’m having fun, but I still notice the electron.
It won’t bother me if the electron hangs around.
I guess I’ll just wander around out here.
I’m happy hanging out here.
The center is cool, but sometimes it can be a “Bohr”.
Electrons circle around the nucleus of an atom.
Protons are a main part of the nucleus of an atom.
Neutrons also hang out in the nucleus of an atom.
Electrons have a negative charge. 
Protons have a positive charge. +
Neutrons have no charge.
0
Electrons are little and have a mass of almost zero.
Protons are big and have a mass of one.
Neutrons are also big and have a mass of one.
What is the structure of an atom?
• Nucleus – center of the atom
– Home of Protons and Neutrons
– Proton
• Has a positive (+) charge
• Has a relative mass of 1
• Determines the atomic number
• Found inside the nucleus
What is the structure of an atom?
– Neutron
• Has no (0) charge
• Has a relative mass of 1
• Determines the isotope
– Isotopes are two of the same
element with different masses
• Found inside the nucleus
What is the structure of an atom?
• Electron
– Has a negative (-) charge
– Has a relative mass of 0 (zero)
– Determines the ion
– Found outside the nucleus
• Bohr model – electrons are in specific
energy levels
• Electron cloud model – electrons are in a
random cloud
What is the structure of an atom?
Bohr Model
Schrödinger Model
“Planetary Model”
“Electron Cloud Model”
How are P, N,
e
related?
• # protons = atomic number
• # electrons = # protons in a neutral atom
• # protons + # neutrons = atomic mass
What is a chemical symbol?
• Chemical symbol tells us what atom it is
• Always a CAPITAL LETTER, sometimes
followed by a lower case letter
• Ex: Oxygen O Nitrogen N Sodium Na
• *Cobalt – Co *Carbon Monoxide – CO
• (Co is an element, CO is a compound)