Transcript Ch5PeriodicTable1 - MrsHamlinsScienceWiki

Chapter 5
The Periodic Table
5.1 Organizing the Elements
Mendeleev’s Proposal
He arranged the elements in order of
increasing mass so that elements with
similar properties were in the same
column
5.1 Organizing the Elements
Mendeleev’s Prediction
He used the properties of existing
elements to predict properties of
undiscovered elements
5.1 Organizing the Elements
Evidence supporting Mendeleev’s table
The close match between Mendeleev’s
predictions and the actual properties of
new elements showed how useful his
periodic table could be
5.1 Organizing the Elements
Until 1750, there were only 17 known
elements
As the number of known elements grew,
the need for organizing the elements also
increased
1789-Antoine Lavoisier
Grouped elements into categories called:
Metals, nonmetals, gases, and earths
5.1 Organizing the Elements
Took 80 years for a better organizing
principle to be found
Dmitri Mendeleev found such a principle
1860’s-working on a chemistry textbook
63 known elements
Put element’s information (mass, name, &
properties) on cards
Lined up cards in order of increasing mass
A pattern emerged-->the key was to break the
elements into rows
5.1 Organizing the Elements
Mendeleev’s chart was a periodic table
Periodic Table- is an arrangement of
elements in columns based on a set of
properties that repeat from row to row
5.1 Organizing the Elements
Mendeleev had to leave empty spaces in his
table, so that the elements that were
already discovered could be placed in the
columns of elements with similar properties.
He predicted that undiscovered elements
would fit in the empty spaces
His prediction was pretty accurate
A good way to test a scientific model is to see if
the model can make accurate predictions (his
did)
5.1 Organizing the Elements
D.M. predicted the
New element
element below Al on
discovered in 1875:
his table would
Named Gallium
have these
Soft metal
properties:
Melting point of 29.7
Soft metal
Low melting point
Density of 5.9 g/cm3
˚C
Density of 5.91
g/cm3
5.1 Organizing the Elements
Mendeleev’s table
Could predict the properties of
undiscovered elements
Could explain the chemical behavior of
different groups of elements
5.2 The Modern Periodic Table
Periodic Pattern
The scales on a piano are an example of a
periodic pattern
Something that repeats at regular
intervals has a periodic pattern
5.2 The Modern Periodic Table
In the modern Periodic Table, elements
are arranged by increasing atomic
number (# of protons), not by
increasing mass like Mendeleev’s table
5.2 The Modern Periodic Table
The Periodic Law
Properties of elements repeat in a
predictable way when atomic numbers are
used to arrange elements into groups
5.2 The Modern Periodic Table
Periods
Each row on the periodic table is called a
period
The number of elements per row varies
because the number of available orbitals
increases from energy level to energy
level
5.2 The Modern Periodic Table
Energy Levels and Periods
The first energy level has only one orbital and a
maximum of two e-’s can fit in it
That is why there are only two elements in the first
period
 H has 1 e-; He has 2 e-’s
The second energy level can fit 8 e-’s
That is why Li starts the second period
 Li has 3 e-’s, two can fit in the first energy level and the
third goes in the second
5.2 The Modern Periodic Table
Groups
Each column on the periodic table is
called a group or family
All the elements in a group have similar
electron configurations
e- configuration determines chemical
properties
Therefore, elements in the same group have
similar properties
5.2 The Modern Periodic Table
Atomic Mass
A value that depends on the distribution
of an element’s isotopes in nature and the
masses of those isotopes
Atomic Mass Unit (amu)
Defined as 1/12 the mass of a carbon-12 atom
This unit is used because the mass of an atom
in grams is very small and not very useful
5.2 The Modern Periodic Table
Classes of Elements
Classified by state of matter
Solids, liquids, gases
Classified by whether or not the element
occurs naturally on Earth or not
Classified by properties
Metals, nonmetals, metalloids
5.2 The Modern Periodic Table
Metals
Elements that are good conductors of
electric current and heat
Solid at room temp. (except for Hg)
Most are malleable
Many ductile
Some highly reactive, some not very
reactive
5.2 The Modern Periodic Table
Metals
Transition Metals
Many will form compounds with distinctive
colors
Elements in the lanthanide series are so
similar that scientists had a hard time
isolating the separate elements
5.2 The Modern Periodic Table
Nonmetals
Elements that are poor conductors of heat and
electric current
Many are gases at room temp. because of their
low boiling pts.
Nonmetals that are solid at room temp are brittle
Some highly reactive, some not reactive at all
F is the most reactive nonmetal
5.2 The Modern Periodic Table
Metalloids
Elements with properties that fall
between metals and nonmetals
Ability to conduct heat and electric current
varies by temperature
Si and Ge are good insulators at low temps and
good conductors at high temps
5.2 The Modern Periodic Table
Variation Across the Period
Across a period from left to right, the
elements become less metallic and more
nonmetallic
5.3 Representative Groups
Valence Electrons
Valence electron-an electron in the
highest occupied energy level of an atom
Electrons in the outermost energy level
Two numbering systems on the periodic table
‘A’ system (1-8), reminds of the atom’s electron
configuration
Elements in a group have similar
properties because they have the same
number of valence electrons
5.3 Representative Groups
Alkali Metals
1 valence electron
Extremely reactive
The reactivity of
alkali metals
increases from the
top to bottom of the
family
Soft metals
Low melting points
Alkaline Earth Metals
2 valence electrons
Harder metals than IA
Higher melting points
Reactivity increases as
you go down the
family
5.3 Representative Groups
 Carbon Family
Boron Family
3 valence electrons
Al is the most
abundant metal in
the Earth’s crust
Metals (4) and one
metalloid
 4 valence electrons
 Nonmetal (1), 2
metalloids, and 3 metals
 Metallic properties
increase as you go down
the family
 Except for H20, most of
the compounds in your
body have carbon in
them
 Known as the element
of life
5.3 Representative Groups
Nitrogen Family
5 valence electrons
2 nonmetals, 2
metalloids, and 1
metal
Metallic properties
increase as you go
down the family
Besides N, fertilizers
often contain P
Oxygen Family
6 valence electrons
3 nonmetals, 2
metalloids, and 1
metal
O2 is the most
abundant element in
the Earth’s crust
5.3 Representative Groups
Halogens
7 valence electrons
4 nonmetals and 1
metalloid
Highly reactive
React with most
metals
Noble Gases
A full outer energy
level (2 or 8 valence
electrons)
Colorless, odorless
Extremely unreactive
or inert