Atomic Structure

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Atomic Structure
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ELEMENTS

• 115 known elements
• 90 naturally occurring elements
• 14 most common elements
• hydrogen (H) carbon (C)
• nitrogen (N) oxygen (O)
• sodium (Na) magnesium (Mg)
• aluminum (Al) silicon (Si)
• phosphorous (P) sulfur (S)
• chlorine (Cl) potassium (K)
• calcium (Ca) iron (Fe)
• CHONPS elements important for life

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ELEMENTS

• all atoms of a specific element have the same
  number of protons
• atoms of different elements have a different
  number of protons
• arranged on Periodic Table to show trends

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PERIODIC TABLE
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ATOMIC SIZE
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SIZE

• 1 mL H2O
• 100,000,000,000,000,000,000,000 atoms
• 1023 atoms
• this is more than the number of drops of water
  in all lakes, rivers, and streams on Earth
• Special microscopes for studying atoms
• transmission electron microscope
• scanning tunneling microscope

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INSIDE AN ATOM
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NUCLEUS

• 1 millionth of the volume of atom
• 99.9 of the mass of an atom
• very, very dense
• contains
• protons
• neutrons

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PROTON p

• positive (1) charge
• mass 1.673 x 10-24 g 1 amu
• amu atomic mass unit
• all identical
• strong nuclear force holds them together

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NEUTRON n0

• NO charge
• mass 1 amu
• all identical
• the number of neutrons can vary for a specific
  element

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ELECTRON e-

• negative (-1) charge
• mass 1/1836 of proton 0 amu
• electron clouds
• space in which e- are likely to be found
• e- whirl around nucleus billions of times per
  second
• impossible to find the exact position of an
  electron
• more energy means a larger electron cloud

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ATOM vs. ION

• ATOM
• of protons of electrons
• NO CHARGE
• ION
• A charged atom
• e- lt p indicates a POSITIVE ION
• CATION
• e- gt p indicates a NEGATIVE ION
• ANION

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SUBATOMIC PARTICLES
Abbreviation Charge Location Mass (AMU) Who? When?
proton p 1 nucleus 1
neutron no 0 nucleus 1
electron e- -1 electron clouds 0
Rutherford 1919
Chadwick 1932
Thomson 1897
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PERIODIC TABLE SYMBOL

• Element Name
• Atomic Number
• of protons
• Element Symbol
• Atomic Mass (amu)

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ATOM SYMBOL (chromium-52)

• Mass Number
• protons neutrons
• Atomic Number
• of protons

Element Symbol
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ATOMIC NUMBER

• Z
• number of PROTONS
• identifies the element
• never, EVER changes for a given element

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MASS NUMBER

• A
• number of PROTONS NEUTRONS
• mass of atom in amu (almost all mass is in the
  nucleus)
• neutrons mass number atomic number

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ISOTOPE

• atoms of the same element that have different
  numbers of neutrons (different mass numbers)
• similar chemical properties, but different mass
• isotopes are named for their mass number, for
  example
• chlorine-35 ? 35Cl
• chlorine-37 ? 37Cl

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ISOTOPE EXAMPLE

• carbon-12
• 6 protons
• 6 neutrons
• carbon-14
• 6 protons
• 8 neutrons

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ISOTOPE EXAMPLE
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ION SYMBOL

• Mass Number
• protons neutrons
• Atomic Number
• of protons

Ion Charge
2
this atom must have LOST 2 ELECTRONS to become a
2 ION
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POSITIVE ION ? CATION

• atom that has lost electrons

• Protons?
• 13
• Neutrons?
• 14
• Electrons?
• 10

Al
3
27 13
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NEGATIVE ION ? ANION

• atom that has gained extra electrons

• Protons?
• 34
• Neutrons?
• 45
• Electrons?
• 36

Se
-2
79 34