Periodic Table
Chapter 2
Development of the Periodic Table
• First version was created by Dmitri Mendeleev in 1869
• Arranged elements by atomic mass
• Noticed that elements in the same column had similar properties
• Left blank spots for elements that hadn’t been discovered yet
Development of the Periodic Table, cont’d
• Problems with Mendeleev’s table:
• Te and I seemed out of place
• Properties did not match other elements in their column
Development of the Periodic Table, cont’d
• Henry Mosely x-rayed elements in 1913
• Was able to count the number of protons in the nucleus
• Rearranged the Periodic Table by atomic number
• Fixed the out of place elements in Mendeleev’s table
Development of the Periodic Table, cont’d
• Today’s Periodic Table is arranged by atomic number
• Periodic law: the cycling of properties seen in the rows of the
Periodic Table
Information About the Elements
• Atomic symbols:
• One capital letter (K, H, O, U, N, C, F)
• One capital letter & one lowercase letter (Na, Mg, Ca, Cu, Cl, He)
• All are assigned by IUPAC
• Elements without names are identified by their atomic
number in Latin (#115 = ununpentium)
Atomic mass
Symbol
Oxidation
states (charges)
Atomic
number
Ground state electron configuration
Periods
• Horizontal rows
• Seven periods
• Period number = number of orbitals in the atom
• Also orbital the valence electrons are in
Groups
• Columns
• 18 groups
• Elements in the same groups have the same number of
valence electrons
• Gives them similar properties
Structure of the Periodic Table
• Metals  left and middle
• Nonmetals  right
• Metalloids  along the bold staircase
1
1
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2
13
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15
16
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2
3
14
3
4
5
6
7
8
9
10
11
12
4
5
6
7
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Figure 2.5: Metals are on the left and in the middle of the Periodic Table, nonmetals are on the
right, and metalloids are in-between.
18
17
Metals
• Most of the elements are metals
• Most active metals = Groups 1 and 2
• Francium (Fr) is the most active metal
of all
• All metals are solids at room
temperature
• Except mercury (Hg)  liquid
Metals, cont’d
• Metals are:
• Malleable  can be shaped
• Ductile  can be drawn into wires
• Shiny (have luster)
• Good conductors of heat and
electricity
• Denser than water (they sink)
Metals, cont’d
• Metals:
• Have low ionization energies (lose
electrons easily)
• Have low electronegativities (don’t
gain electrons easily)
• Make positive ions
Metals, cont’d
• Metallic properties:
• Decrease as you move across a period (left to right)
• Increase as you move down a group
Transition Metals • Metals in the middle of the Periodic
Table
• Groups 3-12
• Have multiple positive oxidation
states
• Can lose different numbers of electrons
to make different ions
• Ex: Cu+ and Cu2+, Fe2+ and Fe3+, Mn4+
and Mn7+
• Ions are different colors
Nonmetals
• All found on the right side of the Table
• Fluorine is the most active nonmetal
• Found as all three phases of matter
• Bromine is the only liquid nonmetal at room temperature
• Hydrogen, nitrogen, oxygen, fluorine, chlorine, and everything in
Group 18 are gases
• Everything else is solid
Nonmetals, cont’d
• Solid nonmetals are dull, soft, and brittle
• Properties of nonmetals:
• Poor conductors of heat and electricity
• Have high ionization energies (difficult to lose
electrons)
• Have high electronegativities (gain electrons
easily)
• Make negative ions
Nonmetals, cont’d
• Allotropes: different forms of the same element that exist in
the same phase of matter
• Have different structures and different properties
• Only seen in nonmetals
• O2 (g) and O3 (g)  oxygen and ozone
• Graphite (pencil lead) and diamond are both carbon
Nonmetals, cont’d
• Some nonmetals are diatomic molecules
• Two identical atoms bonded together
• H2, N2, O2, F2, Cl2, Br2, I2
• BrINClHOF  brinklehof
Metalloids
• Found along the bold line
• Boron (B), silicon (Si), germanium
(Ge), arsenic (As), antimony (Sb),
and tellurium (Te)
• Have some properties of metals and
some of nonmetals
Ionization Energy
• The amount of energy needed to remove the outermost
electron from an atom in the gaseous state
• Metals have low ionization energies; nonmetals have high
ionization energies
• Can be found on Table S
Ionization Energy, cont’d
• From left to right in a period, ionization energy increases
• As the number of protons increases, they attract the electrons more strongly
• Takes more energy to pull off the electrons
• From top to bottom in a group, ionization energy decreases
• Each new orbital is farther away, so the electrons are farther from the nucleus
• Takes less energy to pull off electrons
Atomic Radius
• The distance from the center of the nucleus to the outer edge
of the electron cloud
• Metals are always larger than the nonmetals in the same
period
• Found on Table S
Atomic Radius, cont’d
• From left to right in a period, atomic radius decreases
• As the number of protons increases, they attract the electrons more strongly
• Pulls the electron cloud closer to the nucleus
• From top to bottom in a group, atomic radius increases
• Each new orbital is farther away, so the atom is bigger
Ionic Radius
• The distance from the center of the nucleus of an ion to the
outer edge of the electron cloud
• Metals lose electrons to become smaller
• Nonmetals gain electrons to become larger
Electronegativity
• The measure of an atom’s attraction for electrons
• Abbreviate EN
• High EN = easily attract (gain) electrons
• Fluorine has the highest
• Found on Table S
Electronegativity, cont’d
• From left to right in a period, EN increases
• As the number of protons increases, they attract the electrons more strongly
• From top to bottom in a group, EN decreases
• Each new orbital is farther away, so electrons are less attracted
Summary of Trends
HORIZONTAL TRENDS
V
E
R
T
I
C
A
L
T
R
E
N
D
S
Li
F
High ionization energy
High EN
Small radius
Most active nonmetal
Cs
Fr
Low ionization energy
Low EN
Large radius
Most active metal
Hydrogen
• Nonmetal with 1 electron
• Diatomic
• Does not belong to any Group
• Can lose its electron  H+
• Can gain an electron  H–
Groups 1 & 2
• Group 1 = alkali metals
• 1 valence electron  lose this to become +1 ions
• Most active Group of metals
• Found in nature only in compounds
Groups 1 & 2, cont’d
• Group 2 = alkaline earth metals
• 2 valence electrons  lose these to become +2 ions
• Not as active as Group 1
• Found in nature only in compounds
Groups 3‐12
• Transition metals
• Multiple positive ions
• Colored ions
• Less reactive than Groups 1 and 2
Lanthanides & Actinides
• Metals at the bottom of the Table
• Many are radioactive
Groups 14‐16
• Contain at least one metal, one metalloid, and one nonmetal
• Nonmetals at the top; metals at the bottom
• Carbon, nitrogen, and oxygen are important
Group 17
• Halogens
• 7 valence electrons  gain 1 more to make –1 ions
• Most active nonmetals
• Only Group with at least one of each phase of matter
• F2 and Cl2 = gases
• Br2 = liquid
• I2 = solid
Group 18
• Noble gases
• Do not react  do not make
ions or compounds
• Already have 8 valence
electrons = an octet
• All other atoms lose or gain
electrons to make an octet