1. Periodic Trends

2. History of the Periodic Table  1871 – Mendeleev arranged the elements according to: 1. Increasing atomic mass 2. Elements with similar properties were put in the same row  1913 – Moseley arranged the elements according to: 1. Increasing atomic number 2. Elements with similar properties were put in the same column

3. Two things that we are looking at… 11 8 2234567 3Transition Metals 4 5 6 7 PERIODS (across) GROUPS (down)

4.  Periods:  All of these elements have the same number of electron shells (energy levels)  Examples: P One (H, He) = one orbit, P Two (Li, Be, …) = two orbits...  Groups:  All of these elements have the same electron configuration – same number of electrons in outer orbit (valence electrons)  Examples: Group one = H, Li, Na, K / Group two = Be, Mg, Ca / …  The number of valence electrons is given by the group number  The number of valence electrons increases from left-to-right across the table  Elements in the same group have similar physical and chemical properties

5. Group Names 1 Alkali Metals 2 Alkaline Earth MetalsTransition Metals3456 7 Halogens 8 Noble Gases HHe LiBeBCNOFNe NaMgAlSiPSClAr KCa

6. Atomic Radius  Size of an atom – distance from nucleus to outermost electron  As you move down a group, atomic radius increases  This is because there are more electron orbits  As you move right-to-left across a period, atomic radius increases  This is because atoms with fewer electrons have a weaker attraction force:  less electrons and protons = less attraction = larger radius

8. Reactivity  The tendency of an atom to react  As you move down a group, reactivity increases because the valence electrons are farther from the nucleus and are more easily lost

9.  The “Octet” Rule:  Atoms want to have a stable valence shell  This means that they will react with other atoms to gain/lose electrons to gain a stable valence shell  The fewer electrons needed = the higher the reactivity  Example: H is very reactive because it has only 1 valance electron  Thus H easily loses one  Example: Cl is very reactive because it has 7 valence electrons  Thus Cl easily gains one  This trend makes Alkali Metals (group one) and Halogens (group seven) VERY REACTIVE and Noble Gases (group eight) NON-REACTIVE!

10. Alkali MetalPhysical PropertiesChemical Properties Atom (Bohr- Rutherford Diagram) HOMEWORK LithiumShiny, grey, malleableReacts with water to form H 2 gas SodiumShiny, grey, malleableReacts with water to form H 2 gas (more reactive than Li) PotassiumShiny, grey, malleableReacts with water to form H 2 gas (more reactive than Na) Alkaline Earth Metal Physical PropertiesChemical Properties Atom (Bohr- Rutherford Diagram) HOMEWORK MagnesiumShiny, grey, malleableNo apparent reaction with water CalciumShiny, grey, malleableReacts with water to form H 2 gas (about the same as Li)