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Atoms and Elements

This comprehensive overview of atoms and elements delves into their fundamental structure, including protons, neutrons, and electrons. It explores the concept of elements as pure substances comprised of one type of atom, highlighting over 115 known elements with their symbols and atomic numbers. The document explains the distinctions between isotopes and emphasizes the calculation of atomic mass through weighted averages of naturally occurring isotopes. Additionally, it covers the arrangement of electrons in orbitals and the significance of periodic table organization, connecting atomic structure to chemical properties and reactivity.

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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 Atoms are neutral… so have same # electrons (-) as protons (+)

  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 NOTE: Mass number is used to name isotope 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 Same # protons, different # neutrons Mass Number • Calculated for each individual isotope • Used to name the isotope • Averaged together to represent all carbon All have same # protons

  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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