Section 5.2 The Modern Periodic
Table
• Mendeleev created his periodic table
before the discovery of protons (arranged
his according to atomic weight and
properties).
• Henry Moseley arranged the elements
by increasing atomic number in the
modern periodic table.
• This resulted in a periodic pattern of
properties.
The Modern Periodic Table
• There are 7 rows on the periodic table.
• Rows are called periods.
• The number of elements in a period
varies because of the number of orbitals.
• As you move down into a different row
you add an energy level (or ring) around
the nucleus.
• Each column is called a group (or family).
• There are 18 groups.
• Elements within a group have similar
properties.
• Properties of elements repeat in a predictable
way when atomic numbers are used to
arrange elements into groups.
• Elements in a group have similar electron
configurations (all end the same).
• An element’s electron configuration
determines its chemical properties.
• This pattern of repeating properties is called
the Periodic Law.
• Most periodic tables give at least 4 key pieces
of information for each element.
– 1. The name
– 2. The symbol
– 3. The atomic number
– 4. The 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.
• Units = amu (atomic mass units)
• The mass in grams of an atom is extremely small and
not very useful. Matter contains trillions of atoms.
• Scientist chose one isotope to serve as a standardcarbon.
• They gave 12 atomic mass units to the carbon-12
atom (6 protons, 6 neutrons).
• Now an amu is 1/12 the mass of a carbon-12 atom.
Classes of Elements
There are 3 ways to classify elements.
1. By the elements state of matter-solid, liquid, or gas
(at room temperature).
- solids- black, liquids- blue(purple), and
gasses- red.
2. Divided into two groups based on whether they occur
naturally or are synthetic (man made).
-1-92 occur naturally (all but 2-Tc and Pm). These
are
written in solid colors.
-93 on are synthetic (written in white and outlined
in black).
3. Puts the elements into categories based on
their properties (also called regions).
- These regions are metals, nonmetals and
metalloids.
The 3 Regions (Classifications)-using Fig. 7
p.133
1. Metals• Represented by blue boxes.
• Majority of elements on the periodic table.
Properties of Metals
•
•
•
•
•
•
Good conductors of heat and electricity.
Solids at room temperature (except Hg)
Malleable (most)
Most are ductile.
The left side are extremely reactive.
As you move right across the metals they
become less reactive.
• Lustrous
• Higher boiling points.
2. Nonmetals
Properties of Nonmetals
• Represented by the yellow boxes.
• Poor conductors of heat and electricity.
• Low boiling points (b.p.).
• Can be gases at room temperature (why low b.p.).
• Solids are usually brittle (shatter or crumble).
• Vary in chemical properties as well as physical.
• 1 liquid element- Bromine
• Some are very reactive- group 17- halogens.
• Some are unreactive- group 18- Noble gasses.
3. Metalloids
Properties of Metalloids
• Green boxes on periodic table (8 total)
• Properties fall between metals and
nonmetals.
• Able to conduct electricity but varies with
temperature.
• Si and Ge are good insulators at low
temps. and good conductors at high
temps.
Properties Vary Across a Period
• As you go left to right across a period on the
periodic table the elements become less
metallic and more nonmetallic in their
properties.
• The most reactive metals are on the left sideGroup 1A (alkali metals).
• The most reactive nonmetals are in Group 17
or 7A (halogens).
Transition Metals
• The transition metals are elements that form
a bridge between the left side of the periodic
table(between the s and p blocks).
• They fill the d and f orbitals.
• The lanthanide and actinide series are also
known as the inner transition metals. These
are the two rows below the periodic table.
• Many of these elements have similar
properties even though they are not in the
same groups.
Section 5.3 Representative Groups
Valence Electrons:
• Electrons in the highest energy level (furthest ring
from the nucleus).
• Play a key role in chemical reactions.
• Are the electrons involved in bonding.
• Only come from the s and p orbitals.
• Maximum number is 8.
Elements in groups have similar properties
because they have the same number of valence
electrons.
Group 1 Alkali Metals
• Group 1 (or 1A) metals are the most reactive
metals because they have 1 valence electron.
• They increase in reactivity as you go down the
group.
• Lithium is the least reactive and Cesium and
Francium are the most reactive.
• Sodium and potassium have to be stored in oil
because they react with the oxygen and water
vapor in air.
• Cesium has to be stored in a glass tube filled with
argon because it reacts with water temperatures
as low as -115˚C.
Alkaline Earth Metals
• Are in group 2 (2A) and have 2 valence
electrons.
• They are not as reactive as group 1.
• The differences in their reactivity is shown by
how they react with water.
• Ca, Sr, and Ba react with cold water.
• Mg reacts with hot water and Be does not
react at all with water.
The Halogens
• The halogens are in group 17 or 7A.
• They all have 7 valence electrons and need 1
more to become stable like the noble gases.
• They may have different physical characteristics
but they have similar chemical properties.
• F and Cl are gases, Br is a liquid and I is a solid.
• They are highly reactive nonmetals. Fluorine is
the most reactive in the group. So reactivity
decreases down this group.
• They react easily with most metals.
Noble Gases
• The noble gases are in group 18 or 8A.
• They have 8 valence electrons and are
considered to be stable.
• They are colorless and odorless.
• Helium is placed with the noble gases because
it acts like a noble gas but it only has 2 valence
electrons.
• All noble gases are used in “neon” lights
except for radon.
• They emit light when a current passes through
them.
• All groups with the A labels are called the
representative elements or main group
elements.
• These are the elements that make up the s
and p blocks (orbitals).