Prentice Hall Physical Science
Chapter 5: The Periodic Table
5.1 Organizing the Elements
A. The Search for Order
- Antoine Lavoisier was one of the first to
group the known elements into categories
(metals, nonmetals, gases, and earths) in
1789
- many tried to organize them, by no plan
worked for all the elements
B. Mendeleev’s Periodic Table
- in the 1860s, Dmitri Mendeleev was
working on a book about the 63 known
elements and he models a way to organize
them on a game like solitaire
- he made a card for each element and
then lined the cards up in order of increasing
mass; doing this, he saw a pattern in the way
the elements behaved
- he arranged the elements into rows in
order of increasing atomic mass so that
elements with similar properties were in the
same column (figure 3, p. 127)
- he had arranged a periodic table which is
an arrangement of elements in columns,
based on a set of properties that repeat from
row to row.
- his table was not complete because all of
the elements had not yet been discovered
- he left spaces in his periodic table for
elements that had not been discovered
- based on the position of the spaces and
the properties of the elements around them,
he was able to predict the properties of
these undiscovered elements
belonged in the space under Aluminum
(which he called eka-aluminum) would be a
soft metal with a low melting point and a
3
density of 5.9g/cm .
element (Gallium). It was a soft metal with a
low melting point and a density of 5.91
3
g/cm . It fit into the space that Mendeleev
left.
Mendeleev’s Periodic Table was useful in
predicting the properties of new elements
and helped explain the chemical behavior of
different groups of elements
5.2 The Modern Periodic Table
* the word periodic means repeating
pattern
Ex: days of the week, notes on the scale,
months of the year
The Periodic Law
Mendeleev arranged his periodic table
before protons had been discovered
In the modern periodic table the elements
are arranged in order of atomic number
Periods – a horizontal row on the periodic
table
There are 7 periods corresponding to the
number of energy levels in an atom
Each period contains more elements because
each energy level can hold more electrons
Groups – a vertical column on the periodic
table
Properties of elements repeat in a
predictable way when atomic number are
used to arrange elements in groups
Elements in a group have similar chemical
and physical properties because they have
similar electron configurations
B. Atomic Mass
- because protons are so small, it is hard to
find their mass using traditional units, so
scientists developed the atomic mass unit
(amu) to describe the mass of a proton
- 1 amu = 1/12 the mass of a carbon-12
atom
- every atoms of one element does NOT
have the same number of neutrons so every
atom in one element does not have the same
mass
- atomic mass is the weighted average of
all of the possible atoms in an element
- example: chlorine comes in two forms:
chlorine-35 and chlorine-37 75% is chlorine35, 25% is chlorine-37 its atomic mass is then
25% (37) + 75% (35) = 35.5 amu
Classes of Elements
Metals
-
to the left of the stair-step line
-
good conductors of heat and electricity
- most are solids at room temperature
(only Hg is not)
-
ductile (can be drawn into wires)
-
malleable (can be beaten into sheets)
- some are extremely reactive and some
are not
- transition metals (groups 3-12) are
elements that transition from metals to
nonmetals
-they form compounds with distinctive
colors
-
Nonmetals
-
to the right of the stair-step line
-
properties opposite those of metals
-
poor conductors of heat and electricity
- low boiling points so many are gases at
room temperature
-
if they are solids, they are brittle
- some are extremely reactive and some
are not
-
Metalloids
-
touch the stair-step line on a whole side
-
have properties of metals and nonmetals
D. Variation Across a Period
- across a period from left to right,
elements become less metallic and more
nonmetallic (fig. 13, p. 138)
- the most reactive metals are on the left
and the most reactive nonmetals are in
group 17
- ex: sodium will react violently with
water in the air, but magnesium will only
react with hot water and aluminum will not
react with water
5.3 Representative Groups
*** Valence electrons are the number of
electrons in the outermost energy level of
the atom.
*** Elements in the same group have similar
properties because they have the same
number of valence
electrons.
Group 1 (1A)- Alkali Metals (p. 140)
-
1 valence electron
-
soft, silver-white, shiny metals
-
good conductors of heat and electricity
- never found uncombined in nature
because they are so reactive
-
stored in oil so they don't react with air
-
found in table salt, baking soda, and soap
-
cesium is a liquid
-
lose one electron
-
reactivity increases from top to bottom
Group 2 (2A)- Alkaline Earth Metals (p.141)
-
2 valence electrons
- very reactive (but as reactive as alkali
metals)
-
never found uncombined in nature
- less reactive than alkali metals because
they have to lose 2 electrons instead of one
-
silver-white metals
-
good conductors of heat and electricity
- used in alloys, medicines, flares, and
fireworks
-
calcium in earth's crust and our bones
Group 3-12 - Transition Metals (p. 136)
- have properties similar to one another,
but different from the properties of other
metals
-
1 or 2 valence electrons
-
lose 1 or 2 electrons
-
make brightly colored compounds
-
good conductors of heat and electricity
-
gold and silver make jewelry
-
silver is in photographic film
-
mercury in thermometers
Group 13 (3A) - Boron Family (P. 142)
-
3 valence electrons
-
B is a metalloid, but others are metals
-
B is hard and brittle
-
B is never found uncombined
- B is used in heat resistant glass and the
cleaning compound borax
-
Al is most abundant metal in crust
- Al used in industry to make parts for cars,
trains, and planes
-
Al very malleable
Group 14 (4A) - Carbon Family (p. 142)
-
4 valence electrons
- C nonmetal, Si and Ge are metalloids, Sn
and Pb are metals
- C can make many compounds, called the
basis of life
- branch of chemistry for carbon
compounds is called organic
-
C is sugars, starches, and fuels
- Si is second most abundant element in
earth's crust
- Si in sand, glass, and cement, solar cells
and computer chips
-
Sn is used in lining food cans
- Pb used to be used in color paint and an
additive to gasoline
-
C, NOT Pb, in pencils
Group 15 (5A) - Nitrogen Family (p. 143)
-
5 valence electrons
-
N makes up 78% of air
-
N shares electrons when it bonds
- N in fertilizers, explosives, medicines,
dyes, and ammonia
- P is an active nonmetal not found free in
nature
-
P used in matches, flares, and fertilizers
-
As in insecticides
-
Sb an Bi in alloys
Group 16 (6A) - Oxygen Family (p. 143)
-
6 valence electrons
-
O shares electrons
- O most abundant element in earth's
crust and second in atmosphere
- we breathe oxygen to use to break down
carbohydrates to produce energy
-
plants produce O2
-
O makes up ozone
- S, Se, and Te are brittle solids that
combine with O, metals and H
- S used to manufacture medicines,
matches, gunpowder, and synthetic rubber
-
Se used to make red glass and enamels
-
Te is used in alloys
-
Po is extremely rare
Group 17 (7A) - Halogens (p. 144)
-
7 valence electrons
-
most active nonmetals
-
gain or share one electron
-
never found free in nature
- sodium chloride is an example
compound
- when they react with metals they form
salts
-
NaF is in toothpaste
-
CaCl2 is used to melt snow and ice
-
AgBr is used in photographic film
Group 18 (8A) - Noble Gases (p.145)
-
unreactive
-
called inert
- all but He have 8 valence electrons, He
has 2
- found in small amounts in the
atmosphere
- Argon is most common and makes 1% of
atmosphere
-
not discovered until end of 19th century
-
Neon lights filled with
-
Radon used to treat cancer
Bottom two rows - Rare Earth Elements (p.
136)
-
last two rows
- pulled out because that makes table
shorter and easier to read
-
one or two valence electrons
-
1st row called lanthanoid series
- soft, malleable metals with high luster
and conductivity
-
used to make alloys and glass
-
2nd row called actinoid series
-
all radioactive
- all but 1st three are man-made
(transuranium elements- atomic number
greater than 92)
- best known is U which is used in nuclear
reactors