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Atoms and Elements

Atoms and Elements. Structure of an Atom. Charges Electron – negative Proton – positive Neutron - neutral. Parts Nucleus – neutrons & protons Orbitals - electrons. Elements. Pure chemical substances made up of one type of atom Building blocks of matter

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Atoms and Elements

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  1. Atoms and Elements

  2. Structure of an Atom • Charges • Electron – negative • Proton – positive • Neutron - neutral • Parts • Nucleus – neutrons & protons • Orbitals - electrons

  3. Elements • Pure chemical substances made up of one type of atom • Building blocks of matter • Over 115 elements known - and more being discovered

  4. Elements – Symbol / Name Examples: Latin C Carbon Au Gold-aurum O Oxygen Lb Lead-plumbum Mg Magnesium K Potassium-kalium Br Bromine Na Sodium-natrium Symbol: one or two letter abbreviation

  5. Elements – Atomic Number • ALL Carbon atoms have six protons, and …ALL atoms with six protons are Carbon • BUT… they can have different numbers of neutrons These are called isotopes of carbon DEFINES the element

  6. Elements – Atomic Mass • MASS NUMBER = mass of all particles in one atom (protons, neutrons and electrons) • Measured in “atomic mass units” (amu) Calculated from Mass Number

  7. Elements – Mass Number • MASS NUMBER = mass of all particles in one atom (protons, neutrons and electrons) • Mass of 1 proton = 1 amuMass of 1 neutron = 1 amuMass of 1 electron = really, really tiny! • SO… mass number = # protons + # neutrons • Carbon • 6 protons x 1 amu/proton = 6 amu • 6 neutrons x 1 amu /neutron = 6 amu • 6 electrons x really tiny mass = 0 amu TOTAL = 6 amu + 6 amu + 0 amu = 12 amu

  8. Elements – Mass Number Helium Nitrogen Atomic Number = Mass Number = 2 (protons)4 amu (p + n) Atomic Number = Mass Number = 7 (protons)14 amu (p + n)

  9. Elements – Atomic Mass • BUT… Why is the atomic mass for Lithium (atomic number 3; with 3 protons) = 6.94?!?! • …. Isotopes Lithium-6 - 3 protons, 3 neutrons - mass number = 6 - 7.5% of all lithium Lithium-7 - 3 protons, 4 neutrons - mass number = 7 - 92.5 % of all lithium

  10. Elements – Atomic Mass • BUT… Why is the atomic mass for Lithium (atomic number 3; with 3 protons) = 6.94?!?! • Calculation: Weighted Average (info. only): • 7.5 % Lithium-6 at 6 amu • 92.5 % Lithium-7 at 7 amu • (0.075 x 6 amu) + (0.925 x 7 amu) = (0.45 amu) + (6.48 amu) = 6.93 amu

  11. Elements – Atomic Mass • The atomic mass of an element is calculated by doing a weighted average of the mass numbers of all naturally existing isotopes. • If you round the atomic mass of an element to the nearest whole number, you get the mass number of the most common isotope. 7.0

  12. Elements – Symbol / Name Atomic Mass • “Average” for all carbon • Calculated from mass numbers of isotopes • On the periodic table Mass Number • Calculated for each individual isotope • Averaged together to represent all carbon All have same # protons Same # protons, different # neutrons

  13. Elements - SUMMARY

  14. Structure of an Atom • Outside the nucleus electron • Electron • Atomic mass 0 • Charge (-) nucleus (containing protons and neutrons)

  15. Structure of an Atom • Electrons are arranged in orbits • Orbit 1 holds 2 electrons • Orbit 2 holds 8 electrons • Orbit 3 holds 8 electrons…

  16. Structure of an Atom • Nucleus – the center of an atom contains… • Protons • Atomic mass 1 • Charge (+) • Neutrons • Atomic mass 1 • Charge none

  17. Symbols • Either 1 or 2 letters symbols • First letter Capital, second lower case • Some based on Latin name Example Latin C Carbon Au Gold-aurum O Oxygen Lb Lead-plumbum Mg Magnesium K Potassium-kalium Br Bromine Na Sodium-natrium

  18. The Periodic Table • Elements are arranged by size and chemical properties. • Rows • Period • Size • Columns • Group • Properties

  19. Properties • Properties are related to atomics structure. • The number of electrons in the outer most orbit (valence electrons) determine how an atom will behave in chemical reactions.

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