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
Ex:
He predicted that an element which belonged in the space under Aluminum (which he called
eka-aluminum) would be a soft metal with a low melting point and a density of 5.9g/cm 3.
In 1875, a French scientist discovered a new element (Gallium). It was a soft metal with a low
melting point and a density of 5.91 g/cm3. 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
Prentice Hall Physical Science
Chapter 5: The Periodic Table
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
A. 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
o There are 7 periods corresponding to the number of energy levels in an atom
o Each period contains more elements because each energy level can hold more electrons
- Groups – a vertical column on the periodic table
o Properties of elements repeat in a predictable way when atomic number are used to
arrange elements in groups
o 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 chlorine-35, 25% is chlorine-37
its atomic mass is then 25% (37) + 75% (35) = 35.5 amu
C. 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
Prentice Hall Physical Science
Chapter 5: The Periodic Table
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