Chapter 6
THE PERIODIC TABLE
Section 1
ORGANIZING THE ELEMENTS
Learning Targets
6.1.1 – I can explain how elements are organized in a
periodic table.
6.1.2 – I can compare early and modern periodic
tables.
6.1.3 – I can identify three broad classes of elements.
Searching for an Organizing Principle
 Before the 1700’s only 13 elements were known.
 During the 1700’s many more were discovered – so
how to organize them became the question.
 Chemists used the properties of elements to sort
them into groups.
 1829 JW Dobereiner (German 1780-1849) published
his triad method.
 Only problem was some elements wouldn’t fit into a
triad.
Mendeleev’s Periodic Table
 Many attempts were made to organize the elements.
 1869 Dmitri Mendeleev (Russian) published his.
 Lothar Meyer published about the same time.
 Mendeleev got credit because he was first and could
explain the usefulness better.
 Mendeleev arranged the elements in his periodic
table in order of atomic mass.
 Mendeleev left spaces and predicted elements would
be discovered to fill those spaces.
The Periodic Law
 Mendeleev’s table was not perfect.
 1913 Henry Moseley (British) fixed/tweaked the
periodic table.
 He put the elements in order of atomic number and
it’s been that way since.
 Periodic Law – when the elements are arranged in
order of increasing atomic number, there is a
periodic repetition of their physical and chemical
properties.
Metals, Nonmetals, Metalloids
 IUPAC (International Union of Pure and Applied
Chemistry).
 IUPAC decided labeling groups 1-18 instead of 1A-8A
and 1B-8B would end confusion about groups.
 Three classes of elements are metals, nonmetals, and
metalloids.
Metals
 About 80% of the elements.
 Metal – good conductor of heat and electric current.
 Luster, ductile (pulled into wires), malleable
(pounded into sheets).
Nonmetals
 Basically opposite of metals and they vary among
themselves.
 Nonmetal – poor conductors of heat and electric
current.
 Brittle (shatter when hit with a hammer).
Metalloids
 Fall along stair step line.
 Metalloid (semimetals) – properties similar to
metals and nonmetals.
 Behavior can be changed by changing conditions.
Section 2
CLASSIFYING THE ELEMENTS
Learning Targets
6.2.1 – I can describe the information in a periodic
table.
6.2.2 – I can classify elements based on electron
configuration.
6.2.3 – I can distinguish representative elements and
transition metals.
Squares in the Periodic Table
 The periodic table displays the symbol and names of
the elements, along with information about the
structure of their atoms.
Squares in the Periodic Table Contd.
 Alkali metals – Group 1A elements
 Alkaline Earth metals – Group 2A (from Arabic al
aqali meaning the ashes.
 Halogens – Group 7A (from Greek hals meaning salt
and Latin genesis meaning to be born).
Electron Configurations in Groups
 Elements can be sorted into noble gases,
representative elements, transition metals or innertransition metals based on their electron
configurations.
The Noble Gases
 Noble Gas – Elements in Group 8A
 Sometimes called inert gases because they do not
take part in reactions.
 Look at the highest occupied energy level.
The Representative Elements
 Representative elements – display a wide range of
physical and chemical properties.
 The s and p sublevels of the highest occupied energy
level are not filled.
 For the representative elements the group number
equals the number of electrons in the highest
occupied energy level.
Transition Elements
 Transition metal – highest occupied sublevel and a
nearby d sublevel contain electrons.
 Inner-transition metal – highest occupied sublevel
and a nearby f sublevel generally contain electrons.
Blocks of Elements
 Look at the electron configuration and placement of
the elements.
 All but helium follow a pattern.
Section 3
PERIODIC TRENDS
Learning Targets
6.3.1 – I can describe trends among the elements for
atomic size.
6.3.2 – I can explain how ions form.
6.3.3 – I can describe periodic trends for first
ionization energy, ionic size, and electronegativity.
Trends in Atomic Size
 Atomic radius – one-half the distance between the
nuclei of two atoms of the same element when the
atoms are joined.
 In general, atomic size increases from top to bottom
within a group and decreases from left to right across
a period.
Group Trends in Atomic Size
 As you go down a group the amount of protons
increases but so does the number of electrons in
occupied energy levels so the size gets larger.
Periodic Trends in Atomic Size
 Same thought but there are no more filled sublevels.
 Here the electrons are in the same sublevel so the
charge on the nucleus pulls the electrons closer so
the size gets smaller.
Ions
 Ion – an atom or group of atoms that has a positive
or negative charge.
 Positive and negative ions form when electrons are
transferred between atoms.
 Cation – ion with a positive charge.
 Anion – ion with a negative charge.
Trends in Ionization Energy
 Ionization energy – energy required to remove an
electron from an atom.
 First ionization energy tends to decrease from top to
bottom within a group and increase left to right
across a period.
Group Trends in Ionization Energy
 As the size of the atom increases, nuclear charge, has
a smaller effect on the electrons in the highest
occupied energy level so the energy required to
remove an electron decreases.
Periodic Trends in Ionization Energy
 The nuclear charge increases but shielding remains
constant so it will take more energy to remove the
electrons as you go left to right.
Trends in Ion Size
 Cations are always
smaller than the
atoms from which
they form.
Trends in Ion Size
 Anions are always
larger than the
atoms from which
they form.
Size generally increases
Trends in Electronegativity
 Electronegativity – the ability of an atom of an
element to attract electrons when the atom is in a
compound.
 In general, electronegativity values decrease from
top to bottom within a group.
 For representative elements the values tend to
increase from left to right across a period.
Summary of Trends
 The trends that exist among the properties can be
explained by variations in atomic structure.
 See page 178 for a quick summary (put this in your
notes).
 Elemental Funkiness