Periodic Table Notes

8th Grade Science

History

Dimitri Mendeleev's Periodic Table (1860s)

  • noticed patterns appeared when elements were arranged in order of increasing atomic mass
  • noticed blank spaces left on the table when elements in groups, concluded they were spaces for elements not yet discovered
Modern Periodic Table (early 1900s to present)

  • arranged in order of increasing atomic number (# of protons)

Groups/Families

  • up & down
  • columns
  • elements in a group/family have similar properties
  • they occur because they have the same number of valence electrons

Periods

  • side to side
  • rows
  • arranged into periods because they have the same number of energy levels

Symbols/Names

  • some elements have symbols very different than their names
  • the original name of the element was in another language
  • Examples
  • potassium, K, is kalium in Latin
  • sodium, Na, is natrium in Latin

Hydrogen Stands Apart

  • properties don't match those of any other group
  • Valence Electrons = 1
  • Reactivity = REACTIVE
  • colorless, odorless gas at room temp; low density

Group 1: Alkali Metals

  • Valence Electrons = 1
  • Reactivity = VERY REACTIVE
  • soft; silver colored; shiny; low density
Alkali metals - Chemical elements: properties and reactions (1/8)
Brainiac Alkali Metals

Groups 2 - 16

Reactivity = decreases then slowly increases from left to right

Group 17: Halogens

Valence Electrons = 7

Reactivity = VERY REACTIVE

poor conductors; react violently with alkali metals to form salts; never found uncombined in nature

Comparing the four halogens - Chemical elements: properties and reactions (2/8)

Group 18: NOBLE GASES

  • Valence Electrons = 8
  • Reactivity = NONREACTIVE
  • colorless, odorless gases at room temp
Helium - Periodic Table of Videos
Fun With Gas | MythBusters

Bohr Model

Big image

Energy Levels

each energy level can hold a specific number of electrons

  • 1st level (closest to the nucleus) = 2 electrons max
  • 2nd level = 8 electrons max
  • 3rd level = 8 electrons max

Big image

Valence Electrons

  • electrons located in the outermost energy level of an atom
  • VERY important because they tell us an element's REACTIVITY
  • have the most energy and are involved when elements form chemical bonds
Big image

Electron Dot Diagrams

  • show the number of VEs of an element

Octet Rule

  • RULE OF 8
  • atoms are stable when they have a full outer energy level of electrons (they want a complete octet)
  • they will gain or lose electrons in order to reach 8 valence electrons
  • a full outermost energy level of electrons = STABILITY
  • NOBLE GASES are so stable and nonreactive because they already have a FULL OCTET already. They are NOBLE.
  • Atoms on the LEFT side of the periodic table tend to LOSE their valence electrons to get to a full outer energy level
  • Atoms on the RIGHT side tend to GAIN electrons to get to a full outer energy level