Chemistry / Unit 3: Electrons and the Periodic Table
3.5 Organization of the Periodic Table
Notes
The periodic table arranges elements by increasing atomic number. Elements in a column have similar properties.
- Groups (columns) share the same number of valence electrons. Periods (rows) match the highest energy level being filled.
- Group 1: alkali metals. Group 2: alkaline earth metals. Groups 3 to 12: transition metals. Group 17: halogens. Group 18: noble gases (very unreactive).
- Metals (left) are shiny, conductive and lose electrons. Nonmetals (upper right) are dull and gain or share electrons. Metalloids (along the staircase, like Si) are in between.
- Blocks: s-block (groups 1 to 2), p-block (13 to 18), d-block (transition metals), f-block (lanthanides and actinides).
Practice
Which element is a halogen?
Halogens are group 17: F, Cl, Br, I.
Elements in the same group have similar chemical properties because they have the same:
Valence electrons control bonding, so matching valence counts give similar reactions.
Which element is a metalloid?
Silicon sits on the staircase line and has properties between metals and nonmetals.
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