Download The Atom Notes

What is an atom?
What is an Atom?
• An atom is the smallest unit of ordinary
matter.
What particles are in an atom?
Particles in Atoms
• Protons
• Neutrons
• Electrons
What are the charges of each particle?
• Protons are Positive
• Neutrons are Neutral
• Electrons are Negative
Nucleus
• The nucleus of the atom is made up of
protons and neutrons.
Cloud of Electrons
• Electrons move within a sphere-shaped region
surrounding the nucleus
• Most of an atom’s volume is the space where
electrons move
• Let’s say you are holding a pencil while
standing at the pitcher’s mound in a baseball
stadium. The nucleus would be the size of the
pencil’s eraser. The electrons could be as away
as the top row seats!
Particle Masses
• Mass of 2,000 electrons = Mass of 1 proton
• Mass of 1 proton = Mass of 1 neutron
Particle Masses
• The protons and neutrons make up nearly all
the mass of an atom
Particle Masses
• Particles too small to be measured in
grams/kilograms
• Scientists use atomic mass units (amu)
Particle Masses
• A proton or neutron has a mass equal to
about one amu
• An electron has a mass of about 1/2000 amu.
What is an Element?
What is an Element?
• An atom with a specific number of protons.
 Oxygen Atom
Atomic Number
• The number of protons in an element’s
nucleus.
Atomic Mass
• The sum of the protons and neutrons in the
nucleus of an atom
Isotopes
• All atoms of the same element have the same
number of protons
• However, the number of neutrons can vary.
Isotopes
• Atoms with the same number of protons and
a different number of neutrons are called
isotopes
Isotopes
• An isotope is identified by its mass number.
• (Mass number = protons + neutrons)
Atomic Model
• Atoms are so small, scientists create models to
describe them