Download Document

Section 5-2:
Electron Configuration and
the Periodic Table
Coach Kelsoe
Chemistry
Pages 138-149
Section Objectives

Describe the relationship between electrons in
sublevels and the length of each period of the
periodic table.
 Locate and name the four blocks of the periodic
table, as well as explain the reason for these names.
 Discuss the relationship between group
configurations and group numbers.
 Describe the locations in the periodic table and the
general properties of the alkali metals, the alkalineearth metals, the halogens, and the noble gases.
Periods and Blocks of the Periodic
Table

Remember that elements are arranged vertically in
groups and horizontally in periods.
 Elements in the same group share chemical
properties.
 The length of each period is determined by the
number of electrons that can occupy the sublevels
being filled in that period.
Periods and Blocks of the Periodic
Table
 The
first period consists of two elements
because the 1s sublevel can only 2 electrons.
 In the second period, the 2s sublevel can hold
two electrons and the 2p sublevel can hold 6,
so the second period has 8 elements.
 The same applies to the third period.
 At the fourth period, the 4s sublevel can hold
2 electrons, the 3d sublevel can hold 10
electrons, and the 4p sublevel can hold 6.
Periods and Blocks of the Periodic
Table
 The
period of an element
can be determined from the
element’s electron
configuration.
 For example, arsenic (As)
has the Noble Gas
configuration [Ar]3d104s24p3.
The 4 in the 4p3 indicates
that the highest occupied
energy level is the fourth
energy level.
Periods and Blocks of the Periodic
Table
 Based
on the electron
configurations of the
elements, the periodic table
can be divided into four
blocks, the s, p, d, and f
blocks.
 The name of each block is
determined by whether an s,
p, d, or f sublevel is being
filled in successive elements.
Important Notice
 It
is important to
realize that not all
periodic tables have
the information
arranged in the same
way.
 Atomic numbers will
never have a decimal
and will always be in
numerical order.
The s-Block Elements: Group 1 & 2
 The
elements of the s block are chemically
reactive metals.
 Group 1 elements are extremely reactive
because of how easily they lose their electron.
 Using n for the number of the highest
occupied energy level, the outer, or group,
configurations of the Group 1 and 2 elements
are written as ns1 and ns2 respectively.
Alkali Metals
 The
elements of Group 1 of
the periodic table (lithium,
sodium, potassium,
rubidium, cesium, and
francium) are known as the
alkali metals.
 In pure state, all have a
silvery appearance and are
soft enough to be cut with a
knife.
Alkali Metals
 Properties





of alkali metals:
Silvery appearance
Soft in texture
Not found in nature as free
elements because they
combine with other elements.
Combine vigorously with
most nonmetals
React strongly with water to
produce H2 gas and alkalis.
Alkali-Earth Metals
 The
elements of Group 2 of
the periodic table (beryllium,
magnesium, calcium,
strontium, barium, & radium)
are called the alkali-earth
metals.
 Atoms of alkali-earth metals
contain a pair of electrons in
their outermost s sublevel.
Alkali-Earth Metals
 The
Group 2 metals are
harder, denser, and
stronger than the alkali
metals.
 They also have higher
melting points.
 They are less reactive than
alkali metals, but they too
are too reactive to be found
free in nature.
Hydrogen and Helium
 Hydrogen
and helium are special
cases in the periodic table.
 Hydrogen has an electron
configuration of 1s1, but it does
not share the same properties as
the elements of Group 1.
 Helium is also different from the
Group 18 elements. It is very
stable because its outermost
energy level is filled by 2
electrons.
Sample Problem
 Without
looking at the periodic table, give the
group, period, and block in which the element
with the electron configuration [Xe]6s2 is
located.

Group 2, Period 6, Block s
 Without
looking at the periodic table, write the
electron configuration for the Group 1 element
in the 3rd period. Is this element likely to be
more active or less active than the previous?

1s22s22p63s1; it is likely to be more reactive
The d-Block Elements: Groups 3-12
 For
energy level n, there
are n possible sublevels, so
we don’t see the d sublevel
until the 3rd energy level.
 Remember that the 3d
sublevel is higher in energy
than the 4s, so they will fill
up in order of 4s3d.
 The d sublevel is made up
of 5 orbitals that can hold a
total of 10 electrons.
The d-Block Elements: Groups 3-12
 The
group configuration for
Group 3 is (n-1)d1ns2.
 The group configuration for
Group 12 is (n-1)d10ns2.
 There are a few exceptions.
For elements like Palladium
and Platinum, those lower
energy levels do not fill up
first.
The d-Block Elements: Groups 3-12
 The
d-block elements are
metals with typical metallic
properties and are often
referred to as transition
elements.
 They are good conductors
of electricity, have a high
luster, and are less reactive
than alkali and alkali-earth
metals.
Essentials for Life
 These
elements are essential
for life and make up over
96% of the human body.






Carbon
Hydrogen
Oxygen
Phosphorus
Sulfur
Nitrogen
Sample Problem
 An
element has the electron configuration
[Ar]3d84s2. Without looking at the periodic
table, identify the period, block, and group in
which this element is located.



4th Period – indicated by the highest occupied
energy level
d-block – indicated by the (n-1)d1-10ns0-2 notation
Group 10 – indicated by the total number of
electrons in the outer energy level.
The p-Block Elements: Groups 13-18
 The
p-block elements
consist of all the elements
of Groups 13-18 except
Helium.
 Electrons add to a p
sublevel only after the s
sublevel in the same
energy level is filled.
 Atoms of all p-block
elements contain two
electrons in the ns sublevel.
The p-Block Elements: Groups 13-18
 The
p-block elements
and the s-block
elements are called the
main-group elements.
 For Group 13, the group
configuration is ns2np1.
 For Group 18, the group
configuration is the
ns2np6.
The p-Block Elements: Groups 13-18
 For
atoms of p-block
elements, the total number
of electrons in the highest
occupied level is equal to
the group number minus 10.
 In the p-block elements,
there are metals, metalloids,
and nonmetals.
The Halogens

The elements of Group 17
(fluorine, chlorine, bromine,
iodine, and astatine) are known
as the halogens.
 The halogens are the most
reactive nonmetals.
 They react with most metals to
form salts.
 For all atoms, reactivity is based
on the presence of electrons in
the outermost energy level.
The Halogens
 Characteristics
of some of
the halogens:




Fluorine and chlorine are
gases at room temperature.
Bromine is a reddish liquid.
Iodine is a dark purple solid.
Astatine is a synthetic
element prepared in only very
small quantities.
Metalloids
 Metalloids
are
semiconducting elements
that are mostly brittle solids
with some properties of
metals and some of
nonmetals.
 The metalloids have
electrical conductivity
intermediate between that
of metals and nonmetals.
Properties of p-Block Elements
 The
p-block elements are
generally harder and
denser than the s-block
elements, but softer and
less dense than the dblock elements.
 With the exception of
bismuth, these metals are
sufficiently reactive to be
found in nature only in the
form of compounds.
Sample Problem
 Without
looking at the periodic table, write the
outer electron configuration for the Group 14
element in the second period. Then name the
element.



It is in the p-block because its group is higher
than 12
The total number of electrons in the highest
occupied s and p sublevels is equal to the group
number minus 10, so 14-10=4
Being in the 2nd period, it must be 2s22p2.
The f-Block Elements: Lanthanides
and Actinides
 The
f-block elements are wedged between
Groups 3 and 4 in the 6th and 7th periods.
 With seven 4f orbitals to be filled with two
electrons each, there are a total of 14 f-block
elements between lanthanum and hafnium.
 There are also 14 f-block elements between
Actinium and Rutherfordium.