1. Periodic Table
Section 18.3

2. Periodic Table Periodic- Repeated in a pattern
Elements are ordered by:
increasing atomic number
changes in physical & chemical properties
Mendeleev- Ordered elements by atomic mass
Left blank places in his table to line up elements according to their properties
Elements were later discovered and fit into the places he left blank

3. Periodic Table
Moseley- organized elements by atomic number rather than atomic mass
Same arrangement as today
Groups/Families- vertical columns of the periodic table
Electrons
Around the nucleus in an electron cloud
Energy levels dictate location of electrons
Closer to nucleus = less energy
Fill energy levels from inner to outer levels

4. Electrons
Electrons in outer shell – determine chemical properties of elements
Complete outer shell- needs 8 electrons to be stable
Energy levels and # of electrons in each:
Level 1 Holds 2
Level 2 Holds 8
Level 3 Holds 18
Level 4 Holds 32

5. Valence Electrons
Group 1A – 8A have 1-8 valence electrons- See periodic table for details
Electron dot diagrams- A symbol of an element surrounded by dots to represent electrons in the outer energy level
Properties of elements in the same group- similar due to same # of valence electrons

6. Arrangement of Periodic Table
Halogens- group 7A
Likely to react with Alkali metals- group 1A
Rows of Periodic Table- periods
Properties of metals- lustrous, conductive for heat and electricity, malleable, ductile (located in middle and left of periodic table)
Properties of nonmetals- brittle, often gases, don’t conduct
Properties of metalloids- have properties of both metals and nonmetals

7. Building Blocks of Universe
Hydrogen and Helium
Combine to form elements with larger atomic numbers – can only occur through nuclear reactions