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Introductions to Atoms Chapter 4
development of the atomic theory, the atom
16
Science
8th Grade
10/28/2010

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Term
Atom
Definition
  • smallest unit of an element
  • maintains the properties of that element
  • is made up of matter
Term
Electron
Definition
  • subatomic particle
  • has a negative charge
  • found outside the nucleus
Term
Nucleus
Definition
  • "brain of the atom"
  • made up of protons & neutrons
Term
Electron Cloud
Definition

a region (place) around the nucleus of an atom

  • likely place to find electrons
Term
Dalton's Atomic Theory
Definition
  • all substances are made of atoms. Atoms are small particles that cannot be created, divided, or destroyed
  • Atoms of the same element are exactly alike, & atoms of different elements are different
  • Atoms join with other atoms to make new substances
Term
Parts of the Atom
Definition
  • nucleus (center of the atom)
  • Protons (+ charge inside the nucleus)
  • Neutrons (neutral - no charge inside the nucleus)
  • Electrons (- charge outside the nucleus in the electron cloud)
Term
Proton
Definition
  • subatomic particles
  • positive charge
  • found in the nucleus of the atom
Term

Atomic Mass Unit

(amu)

Definition
  • Expresses the mass of an atom or particle
  • Each proton has a mass of about 1 amu
Term
Neutron
Definition
  • subatomic particle
  • has no charge
  • found in the nucleus of the atom
Term
Name the two kinds of particles that can be found in the nucleus
Definition
  1. Protons
  2. Neutrons

 

Term
Ion
Definition
  • a charged atom or molecule.
  • It is charged because the number of electrons do not equal the number of protons in the atom or molecule.
Term
Atomic Number
Definition
  • the number of protons (+ charge) in the nucleus of the atom
  • all atoms of an element have the same atomic number
Term
Isotope
Definition
  • have the same number of protons but have different numbers of neutrons
Term
Properties of Isotopes
Definition
  • Radioactivity - caused by an atom with a nucleus that will change over time
  • radioactive atoms spontaneously fall apart after a certain amount of time
  • when they fall apart they give off energy
Term
Mass Number
Definition
Sum of protons and neutrons in an atoms
Term
Atomic Mass
Definition
  • the mass of an atom expressed in atomic mass unit (amu)
  • the number of protons & neutrons
  • it's a weighted average of natural isotopes of an element
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