Atoms

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Atoms

• Chapter 4 Section 1

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MODERN Atomic Model

• What is an Atom?
• The smallest particle from which all element are
  made.
• Nucleus
• The core of the atom that contains two different
  subatomic particles Protons and Neutrons
• Protons
• Positively charged particles n an atoms nucleus
• Neutrons
• Neutrally charged particles in an atoms nucleus
• Electrons
• Negatively charged particles in a cloud-like
  region that surrounds the nucleus of the atom.

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The Bohr ModelShows the nucleus with electron
orbits surrounding. Electrons have specific
energy levels.
Neutrons have not been discovered at this point!
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Energy Levels Electrons of different energy
levels are located at different locations around
nucleus

• Level 1 Holds up to 2 electrons
• Level 2 Holds up to 8 electrons
• Level 3 Holds up to 8 electrons

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Modern Atomic ModelNucleus surrounded by an
Electron Cloud
Notice Neutrons have now been added. They are
found in the nucleus with the protons!
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Brain Break!

• Stand up lets play Simon says!

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Atomic Number

• Every atom of a given element has the same number
  of protons.
• Atomic Number the number of protons in the
  nucleus of an atom.
• Atoms with different atomic numbers are atoms of
  different elements.

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Calculating the Number of Electrons

• The of Electrons The of Protons.
• Atomic Number Protons, and therefore,
  Electrons

7 electrons
7 protons
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Mass Number

• Protons and Neutrons make up nearly all the mass
  of an atom.
• Protons and Neutrons are about equal in mass.
• Mass Number the sum of the protons and neutrons
  in an atom.

Particle Symbol Charge Relative Mass
Proton p 1 1
Neutron n 0 1
Electron e- 1- 1/1,836
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Calculating the Number of Neutrons

• Atomic Number Atomic Mass of Neutrons

This element is Nitrogen. Its mass is 14. So
atomic of 7, minus atomic mass of 14, equals 7
neutrons.
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What is the Atomic Number?Why is the Mass Number
12?
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Isotopes

• Atoms of the same element that have different
  numbers of neutrons.
• Do you think Isotopes of the same element have
  different mass numbers?
• Do they have different atomic numbers?

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