Periodic Table
CHAPTER 4
History of the Periodic Table
 Dmitri Mendeleev wrote the first periodic
table.
 He arranged elements in order of atomic
mass.
 He noticed repeating properties.
Mendeleev’s periodic table
Moseley’s periodic table
 Moseley rearranged the elements by atomic
number.
Organization of the p.t.
 There are 18 groups or families (columns).
 All elements in a group have the same number of
outer level (valence) electrons.
 There are 7 periods (rows).
 All elements in a period have electrons on the
same energy level.
Group 1 metals
 Called alkali metals.
 They all react violently with nonmetals.
 They have 1 valence electron which they lose
very easily.
 Li is the least reactive, Fr is the most reactive
 They are all soft
 They are not found in nature because they are so
reactive.
Group 2 metals
 Called Alkaline Earth Metals
 They have 2 valence electrons.
 They are harder and less reactive than group
1 metals.
Group 17
 Called halogens
 Most reactive nonmetals
 They all have 7 valence electrons
 They react with metals to form “salts”
Group 18
 Noble gases
 They don’t react
 They have 8 valence electrons (except
Helium)
 This is a full outer level
Metals
 Most elements are metals
 Metals are good conductors of heat and
electricity
 Metals are ductile (can be squeezed into a
wire)
 Metals are malleable (can be hammered or
bent)
Transition Metals
 Groups 3 – 12
 They have many different properties
 Less reactive than alkaline earth metals
 Some are fairly non-reactive (Cu, Ag, Au)
 Tungsten has the highest melting point
 Mercury is a liquid with high density
 Metals can be mixed together (alloy) to produce
desirable properties.
F - Block
 Lanthanides (group 4f)
 #58 – 71
 Actinides (group 5f)
 #90 - 103
Ionization Energy
 The energy required to remove an electron.
 If an electron is easy to remove, it takes little
energy.
 Period Trend
 As you go from left to right across the period, it is
harder to remove an electron – I.E. increases
 Group Trend
 As you go down a group, it is easier to remove an
electron – I.E. decreases
Atomic Radius
 Size of an atom
radius
Half the distance between 2 adjacent nuclei
Atomic Radius
 Period Trend
 As you go from left to right across a period,
atomic radius decreases
 Group Trend
 As you go down a period, atomic radius increases.
Electron Affinity
 Energy change when an atom gains an
electron.
 Period Trend
 As you go from left to right across a period,
electron affinity increases.
 Group Trend
 As you go down a group, electron affinity
decreases.
Electronegativity
 Ability to attract electrons
 0–4
 Period Trend
 As you go from left to right across a period,
electronegativity increases.
 Group Trend
 As you go down a group, electronegativity
decreases.
Ions
 An ion is an atom that has lost or gained
electrons.
 Lose electrons – (+ ion)
 Called cation
 Gain electrons – (- ion)
 Called anion