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The Discovery of Neutrons Isotopes The Discovery of Neutrons

Subatomic Particles Particles found inside the atom Electrons The number of electrons vary for atoms of a single element. The # of electrons = the # of protons in a neutral atom Negative Revolve around the nucleus Mass = 1/1836amu or 0 because it is so small

Subatomic Particles Protons The # of protons determines what element the atom is. Every H has 1p, C has 6, He has 2…. Positive Found in the nucleus Mass = 1amu

Subatomic Particles Neutrons The number of neutrons vary for atoms of a single element. H can have 0, 1, or even 2 neutrons. Neutral Found inside the Nucleus Purpose is to hold repelling protons together Mass = 1amu

Summary of Subatomic Particles Location Mass Relative Mass Charge Proton Electron Neutron Nucleus 1.67 × 10−27 kg 1 amu +1 Outside 9.11 × 10−31 kg 0 amu −1 Nucleus 1.67 × 10−27 kg 1 amu

Oops! Dalton Goofed! mass. Dalton’s discovery of atoms depended on one major characteristic of atoms . . . One of Dalton’s postulates says the following about mass: But in 1911 while trying to study the atomic nucleus, J. J. Thomson accidently discovered that neon could have two different atomic masses. He called them… mass. Atoms of an element are identical. They have the same mass.

Isotopes The electrons and protons. Atoms of the same element with different atomic masses. Atoms of the same element have the same properties. But what causes the chemical properties of an atom? So atoms of different isotopes of an element must have the same number of protons and electrons. Whatever causes isotopes to have different masses must be an electrically neutral particle. The electrons and protons.

The Discovery of Neutrons In 1930, scientists showed that bombardment of beryllium with alpha particles produced neutral radiation. Measurements by Sir James Chadwick in 1932 proved that this neutral radiation was a particle with a mass similar to a proton. This neutral particle is called a neutron. James Chadwick

x A Z Isotopic Notation Element symbol (X) Atomic number (Z) # of protons Mass number or Atomic mass (A) # of protons + # of neutrons Example: x A Z

Naming Isotopes Put the mass number after the name of the element. 12C Carbon-12 or C-12 14C Carbon-14 or C-14 235U Uranium-235 or U-235

Na Practice 24 11 Find the number of protons number of neutrons number of electrons Atomic number Mass Number Name 24 Na 11

Br Practice 80 35 Find the number of protons number of neutrons number of electrons Atomic number Mass Number Name 80 Br 35

Practice An element has an atomic number of 34 and a mass number of 78 what is the number of protons number of neutrons number of electrons Complete symbol Name

Practice An element has 91 protons and 140 neutrons what is the Atomic number Mass number number of electrons Complete symbol Name

Practice An element has 78 electrons and 117 neutrons what is the Atomic number Mass number number of protons Complete symbol Name