Download Unit 8 Summary

Unit 8 Periodic Table SUMMARY
HISTORY/DEVELOPMENT
Dobereiner – 1817, organized the known elements into triads (groups of 3) based on appearance and reactions
Newlands – 1864, organized the known elements into octaves (groups of 8) based on properties
Mendeleev – 1869, considered the father of the modern periodic table; organized the known elements into columns and
rows based on increasing (relative) atomic mass so that properties repeated themselves; left holes in his periodic table
for yet undiscovered elements and predicted the properties and masses of these unknown elements (his predictions
were correct!)
Moseley – 1913, organized the known elements by atomic number (number of protons); this only moved around a few
elements from Mendeleev’s table
Seaborg – 1930s, formulated the Actinide concept of heavy elements and how they connected to the existing periodic
table
LAYOUT
Groups – vertical (up and down) columns, 1-18, atomic number increases top to bottom, elements in same group share
similar physical and chemical properties
Periods – horizontal (across) rows, 1-7, atomic number increases from left to right
alkali metals – group 1
alkaline earth metals – group 2
halogens – group 17
noble gases – group 18
transition metals – groups 3-12
lanthanide and actinide series (also called inner transition metals) – bottom 2 periods
metalloids – along the bolded staircase, excluding Aluminum (Al) and Astatine (At)
metals – left of metalloids, except for Hydrogen (H)
nonmetals – right of metalloids, plus Hydrogen (H)
PROPERTIES OF ELEMENTS
Effective nuclear charge (Zeff) – attraction of the + nucleus for the valence electrons in an atom;
Zeff = # protons - # core electrons (this is only used to compare elements in the same period)
Atomic radius – describes the size of an atom; half the distance between adjacent nuclei; measured in Angstroms (0.1
nm or 1 x 10-10 m)
Ionic radius – describes the size of an ion; half the distance between adjacent nuclei of an ion; measured in Angstroms
(0.1 nm or 1 x 10-10 m)
Electronegativity – a chemical property that describes how strongly an atom attracts bonding electrons towards itself;
no units because it is relative
Ionization energy – a physical property that describes the energy required to remove an electron from an atom; typically
measured in kJ/mole; 1st ionization energy is energy required to remove the 1st valence electron from an atom
(chemical) Reactivity – depends upon the relative attraction between valence electrons of one element and the nucleus
of another element
TRENDS
Effective nuclear charge (Zeff) – increases from left to right across a period (because the # of protons increases but the
number of shielding electrons doesn’t change) and decreases within a group (because the distance between the +
nucleus and valence electrons increases)
Atomic radius – increases from right to left across a period and from top to bottom in a group; Cesium (Cs) has the
largest atomic radius (because Fr is not stable enough to get accurate measurements)
Ionic radius
metals form cations (+ charged ions); cations are smaller than the atom from which they are formed because the
cation has lost valence electrons; this results in an increased P:E ratio when compared to the atom
nonmetals form anions (- charged ions); anions are larger than the atom from which they are formed because
the anion has gained valence electrons; this results in a decreased P:E ratio when compared to the atom
Electronegativity – increases from left to right across a period (but DOES NOT include the noble gases group, because
they do not form bonds) and from bottom to top in a group; Fluorine (F) has the highest electronegativity value
Ionization energy – increases from left to right across a period and from bottom to top in a group; Helium (He) has the
highest ionization energy
(chemical) reactivity – for metals, increases from right to left across a period and from top to bottom in a group;
Francium (Fr) is the most reactive metal; for nonmetals, increases from left to right across a period (excluding the noble
gases) and from bottom to top in a group, Fluorine (F) is the most reactive nonmetal