1. Adapted from Harris Middle School: NEISD
Atom Notes
Adapted from Harris Middle School: NEISD

2. An atom is the basic unit of all matter
An atom is the basic unit of all matter. It is the smallest particle into which an element cannot be broken down into a simpler substance.
There are 2 main locations in an atom:
atomic nucleus (the center with most of the mass of the atom)
electron cloud (surrounds the nucleus)
There are 3 subatomic particles in an atom:
subatomic means smaller (than the atom itself)
3 particles = protons, neutrons and electrons
the numbers of these particles make atoms
different from one another.
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3. Name of subatomic particle Charge of Particle Where it is found
Size/mass
proton
Positive (+)
inside the nucleus- identifies the atom
1 atomic mass unit
electron
Negative (-)
in electron cloud / orbiting around nucleus- determines reactivity of element
Almost zero
1/1836 amu
(very small!)
neutron
Neutral (0)
inside the nucleus- just adds mass/weight
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5. the atomic # = # of protons = element’s identity
periodic table: chart where all elements are arranged by atomic number and properties-this is your cheat sheet to make models of atoms!!
the atomic # = # of protons = element’s identity
# of electrons = # of protons in an atom (neutral)
Symbol is 1 or 2 letters- First letter is always capitalized; if it has 2 letters the second is lower case
the atomic mass = # of protons + # of neutrons
# of neutrons= atomic mass – atomic #
atoms of an element can have different numbers of neutrons (these atoms are isotopes)
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6. Label the subatomic particles in the picture:
p+ = proton
n0 = neutron
e- = electron
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Color the protons blue
Color the neutrons red
Color the electrons green