Transcript Chapter 5

Chapter 5
The Periodic Table
5-1 Organizing the
Elements
• What does the word “periodic” mean?
• Periodic: recurring at regular intervals
• Periodic table – is an arrangement of
elements in columns based on a set of
properties that repeat from row to row
Mendeleev 1869
• See Figure 3 on page 127
• Arranged elements according to increasing
atomic mass in rows
• Put elements of similar properties in the
same column
• Left blank spots in table which predicted
properties of elements not yet discovered
Evidence Supporting
Mendeleev’s Table
• Named eka-aluminum to the element that
belonged one space below aluminum on the
table
• 1875- French chemist discovered a new
element and named it gallium (Ga)
• Gallium is a soft metal used in traffic
signals
Similarity of the two
• Eka-aluminum and Gallium were
similar in properties, so they were
determined to be the same
• The close match between
Mendeleev’s prediction and the actual
properties of new elements showed
how useful his periodic table could be
Questions
1. Which of the following is a symbol
for an element?
a. Aluminum
b. Al
c. al
d. AL
Questions
3. What happens to the composition of
matter during a physical change?
Does it change or remain the same?
Questions
2. Is flammability a physical property
or a chemical property?
Questions
4. What does the atomic number of an
element represent?
Question
5. Isotopes of element have different
numbers of
a. Neutrons
b. Electrons
c. Protons
d. nuclei
Question
6. True or False : Electrons in atoms
occupy orbitals in energy levels
5-2 The Modern Periodic
Table
• Mendeleev developed the periodic
table before the discovery of
protons.
• In the modern periodic table,
elements are arranged by increasing
atomic number
Periods
• Each row in the table of elements is called a
period
• Period 1 has two elements
• Periods 2 and 3 have 8 elements
• Periods 4 and 5 have 18 elements
• Period 6 has 32 elements
• There are 7 periods total on the periodic table
• The number of electrons per period varies
because of the number of available orbitals
increases from energy level to energy level
Groups
• Each column on the periodic table is called a group
• The elements within a group have similar
properties
• Properties of elements repeat in a predicable way
when atomic number are used to arrange elements
into groups
• The pattern of repeating properties is the
periodic law
• There are 18 groups on the periodic table
Atomic Mass
• Atomic mass is a value that depends
on the distribution of an element’s
isotopes in nature and the masses of
those isotopes
• An atomic mass unit (amu) is defined
as one twelfth the mass of carbon-12
atom
Average Atomic Mass
• Weighted average of the
atomic masses of the
naturally occurring
isotopes of an element
What is the aver. atomic
mass of the chlorine?
Isotope
Isotope Mass
(amu)
% Abundance
Chlorine-35 34.96885
75.771
Chlorine-37 36.96590
24.229
Weighted Averages
• Average Atomic Mass =
•
(isotope mass)(relative abundance[dec]) + (isotope mass)(relative abundance[dec])
• (0.75771)(34.96885amu) +
(0.24229)(36.96590amu)
• =
35.453 amu
ISOTOPES
• Atoms of the same element that
differ in mass
• Have the same # protons but
different # neutrons
Classes of Elements
•
Elements are classified as metals, nonmetals, and metalloids
•
Metal:
– Good conductor of heat & electricity
– Ductile –able to be drawn into a fine wire
– Malleability – can be hammered or rolled into thin sheets
•
Nonmetal
– Poor conductor of heat & electricity
– Brittle
•
Metalloids
– Some characteristics of metals & nonmetals
Beaker Breaker
1.
Isotopes have the same # of _______
but different #of __________
2. What is the name of group 1 on the
periodic table?
3. How many periods are there on the
periodic table?
Transition Metals
• Transition metals are elements that
form a bridge between the elements
on the left and right sides of the
table
The Lanthanides
• The 14 elements with atomic
numbers from 58(cerium, Ce) to
71(lutetium, Lr)
• Similar in chemical and physical
properties
The Actinides
• The 14 elements with atomic number
from 90(thorium, Th) to
103(lawrencium, Lr)
Variation across a period
• Across a period from left to right, the
elements become less metallic and more
nonmetallic in their properties
• Most reactive metals are on the left side
of the table
• Most reactive nonmetals are on the right
in Group 17
5-3 Representative
Groups
• Valence electron – is an electron that is in
the highest occupied energy level of an
atom
• Elements in a group have similar properties
because they have the same number of
valence electrons
• Valence electrons explain the location of
hydrogen, hydrogen has a single electron
Alkali Metals
• Elements in Group 1A are called alkali
metals.
• Single valence electron and are
extremely reactive
• The reactivity of alkali metals
increases from the top of Group 1A
to the bottom
The Alkaline Earth
Metals
• The elements in Group 2A are called alkaline earth metals
• All alkaline earth metals have two valence electrons
• They are harder than group 1A
• Differences in reactivity among the alkaline earth metals
are shown by the ways they react with water
• Calcium, strontium and barium react easily with cold water
• Magnesium will react with hot water. No change appears to
occur when beryllium is added to water
The Boron Family
• Group 3A contains the metalloid
boron.
• Aluminum is the most abundant metal
in the Earth’s crust
• Glass that contains boron is used to
make laboratory glassware such as
flasks
The Carbon Family
•
•
•
•
Group 4A contains nonmetal carbon
Two metalloids – silicon and germanium
Two metals – lead and tin
Except for water, most of the compounds
in your body contains carbon
• Silicon is the second most abundant
element in the Earth’s crust
The Nitrogen Family
• Group 5A contains two nonmetals –
nitrogen and phosphorus
• Two metalloids – arsenic and
antimony
• One metal –bismuth
• Besides nitrogen, fertilizers often
contain phosphorus
The Oxygen Family
• Group 6A has three nonmetals –
oxygen, sulfur, and selenium
• Two metalloids – tellurium and
polonium
• All have 6 valence electrons
• Oxygen is the most abundant element
in the Earth’s crust
The Halogens
• The elements in Group 7A are called
halogens
• They have seven valence electrons
• Despite their physical differences, the
halogens have similar chemical properties
• They are highly reactive nonmetals
• Fluorine is the most reactive
The Noble Gases
• The elements in Group 8A are called the
noble gases
• Helium has 2 valence electrons
• All other noble gases have 8 valence
electrons
• The noble gases are colorless and odorless
and extremely unreactive
• All the noble gases except radon are used
in “neon” lights