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
- 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
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
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
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