Download Chapter 2 The Periodic Table

Chapter 2
The Periodic Table
Periodic Pattern
Classification of the Elements
A. “Metals” vs.”Nonmetals” (Before 1800)
1. Metals - Solids, Lustrous, Malleable, Ductile, Conductors
2. Nonmetals - Solids, Liquids, Gases, Poor Conductors
B. In early 1800’s, 50-60 Elements Known
1. 1829 - Doebereiner - A System of “Triads”
Cl, Br, I
Li, Na, K
S, Se, Te
Ca, Sr, Ba
Fe, Co, Ni
Classification of the Elements
2. 1865 - Newlands - “Law of Octaves”
a. Arranged lightest of known elements by atomic weight
b. Observed a periodicity of eight
H
Li
Be
F
Na
Cl
K
B
C
N
O
Mg Al
Si
P
S
Ca
Ti
Mn Fe
Cr
c. Note: He, Ne, Ar, and Kr were undiscovered
d. Introduced the idea of periodicity
Classification of the Elements
3. 1869 - Mendeleev and Meyer
a. Arranged Elements by Atomic Weight
b. Also Considered Chemical Properties of Elements
c. The Result - A Table in Which the “Families” of
Elements Got Larger
d. Additional Triumph of Mendeleev - Spaces were
Left for Undiscovered Elements
“I began to look about and write down the elements with their atomic
weights and typical properties, analogous elements and like atomic
weights on separate cards, and this soon convinced me that the
properties of elements are in periodic dependence upon their atomic
weights.”
--Mendeleev, Principles of Chemistry, 1905, Vol. II
Features of the Modern Periodic Table
A. The Common Form of the Table is One of Many
B. Periods = Rows
Groups = Columns
C. “A” Groups = “Representative”
“B” Groups = “Transition”
Lanthanides and Actinides = “Inner Transition”
D. Periodic Law - Elements within a given group have similar
chemical and physical properties. These properties change
gradually with an increase in atomic number.
E. The terms metals, nonmetals, and metalloids are still used.
Features of the Modern Periodic Table
A. The Common Form of the Table is One of Many
B. Periods = Rows
Groups = Columns
C. “A” Groups = “Representative”
“B” Groups = “Transition”
Lanthanides and Actinides = “Inner Transition”
D. Periodic Law - Elements within a given group have similar
chemical and physical properties. These properties change
gradually with an increase in atomic number.
E. The terms metals, nonmetals, and metalloids are still used.
Metals
Solids at room temperature, except Hg
Reflective surface - shiny
Conduct heat
Conduct electricity
Malleable - can be shaped
Ductile - can be drawn or pulled into wires
Lose electrons and form cations in reactions
About 75% of the elements are metals
Lower left on the table
Nonmetals
Found in all three states
Poor conductors of heat
Poor conductors of electricity
Solids are brittle
Gain electrons in reactions to become anions
Upper right on the table - except H
Metalloids
Show some properties of metals and some of nonmetals
Also known as semiconductors
= Alkali metals
= Halogens
= Alkali earth metals
= Lanthanides
= Noble gases
= Actinides
= Transition metals
Important Groups
Hydrogen
Alkali Metals-Group IA
Li, Na, K, Rb, Cs, Fr
Alkali Earth Metals-Group IIA
Mg, Ca, Sr, Ba, Ra
Halogens-Group VIIA
F, Cl, Br, I, At
Noble Gases-Group VIIIA
He, Ne, Ar, Kr, Xe, Rn
IA
IIA
VIIA
VIIIA
X2
A periodic table showing only the
representative elements. Chemical
periodicity occurs every eight elements.
Ion Charge and the Periodic Table
The charge on an ion can often be determined from an element’s
position on the Periodic Table.
Ion Charge and the Periodic Table
Atomic Mass
We previously learned that not all atoms of an element
have the same mass - isotopes
Isotopes have identical chemical properties.
In calculations, we generally use the average mass
of all an element’s atoms found in a sample.
We call the average mass the atomic mass
Example : If copper is 69.17% Cu-63 with a mass of
62.9396 amu and the rest Cu-65 with a mass of
64.9278 amu, find copper’s atomic mass.
isotope masses,
isotope fractions
avg. atomic mass
Mass Spectrometry
Ions with a particular velocity pass
through and are deflected into
circular paths by the magnetic field.
Ions with different masses strike the
detector in different regions.
The more ions of a given type, the
greater the response of the detector .
A gaseous sample is
ionized by bombardment
with electrons.
The positive ions thus formed are
subjected to an electrical force by
the electrically charged velocity
selector plates and a magnetic
force by a perpendicular
magnetic field.
80
Hg
200.59
The response of an ion detector converted to a relative scale
The percent natural abundances of the mercury isotopes are
196Hg,
0.146%
201Hg,
198Hg,
13.22%
10.02%
202Hg,
199Hg,
29.80%
16.84%
200Hg,
204Hg,
23.13%
6.85%.
Mass Spectrum of Chlorine
Moles and Calculations
with Moles
Moles
What is an amu ?
1.66 x 10-24 g
We need a conversion to the macroscopic world.
1. How many hydrogen atoms are in 1.00 g of hydrogen?
1.00 g H x
1 H atom
1.66 x 10-24 g H
=
6.02 x 1023 H atoms
Avogadro’s Number
Moles
2. Consider carbon-12 (the most abundant isotope of C)! !
! What is the mass of one carbon-12 atom ?
12
amu
C atom
x 1.66 x 10-24
g
amu
= 1.99 x 10-23
g
C atom
What is the mass of Avogadro’s number of C atoms?
g
6.02 x 1023 C atoms x 1.99 x 10-23
= 12.00 g
C atom
!
Chemical Packages - Moles
Mole = number of particles equal to the number of atoms in 12 g of C-12
The number of particles in 1 mole is called
Avogadro’s Number = 6.0221421 x 1023
1 mole of C atoms weighs 12.01 g and has 6.022 x 1023 atoms.
The average mass of a C atom is 12.01 amu.
Example : Calculate the number of atoms in 2.45 mol of copper
mol Cu
atoms Cu
1 mol = 6.022 x 1023 atoms
Relationship Between
Moles and Mass
The mass of one mole of atoms is called the
molar mass.
The molar mass of an element, in grams, is numerically
equal to the element’s atomic mass, in amu.
The lighter the atom, the less a mole weighs.
The lighter the atom, the more atoms there are in 1 g.
Example : Calculate the moles of carbon in 0.0265 g of pencil lead
gC
mol C
1 mol C = 12.01 g
Example : How many copper atoms are in a 3.10 g of copper?
g Cu
mol Cu
atoms Cu
1 mol Cu = 63.55 g, 1 mol = 6.022 x 1023