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## The Periodic Law

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### The Periodic Law Trends and the Periodic Properties – PowerPoint PPT presentation

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Title: The Periodic Law

1
The Periodic Law
• Trends and the Periodic Properties

2
Friday, September 28
• Take out one piece of paper, label Periodic Trend
Quiz

3
Friday, October 5
• Take out your Chapter 5 Review Packet and one
piece of paper, write name and date

4
Monday, October 1
• Take out your Mystery Element sheet and one piece
of paper. Draw four columns on your sheet and
label

Periodic Property Period Trends/ Why? Group Trends/ Why? Exceptions

5
Tuesday, October 2
• Take out your periodic table and periodic trends
chart from yesterday.
• Turn in any missing Mystery Lab sheets.

6
Mystery Element Lab
• You have a few minutes to finish the electron
configurations on lab

7
Chapter 5, Section 3
• As you read p. 150-164, fill in the table
explaining the property, the trend on periods and
groups, and the reason for the trend.

Periodic Property/ Define Period Trends/ Why? Group Trends/ Why? Exceptions

Atomic Radii Ionization Energy Electron
Affinity Ionic Radii Electronegativety
8
• The boundaries of an atom are fuzzy, and an
atoms radius can vary under different conditions
• Atomic radius may be defined as one-half the
distance between the nuclei of identical atoms
that are bonded together

9
Trends and the Periodic Properties
• The trend to smaller atoms across a period
(increasing groups) is caused by the increasing
positive charge of the nucleus, which attracts
electrons toward the nucleus
• Atoms tend to be larger the farther down in a
group (increasing periods) they are found
• The trend to larger atoms down a group is caused
by the increasing size of the electron cloud
around an atom as the number electron sublevels
increases

10
Trends and the Periodic Properties

11
Trends and the Periodic Properties

12
Trends and the Periodic Properties
• Sample Problem
• Of the elements magnesium, Mg, chlorine, Cl,
sodium, Na, and phosphorus, P, which has the
terms of trends of the periodic table

13
Trends and the Periodic Properties
• Sample Problem Solution
• Sodium has the largest atomic radius
• All of the elements are in the third period. Of
the four, sodium has the lowest atomic number and
is the first element in the period. Atomic radii
decrease across a period

14
Ionization Energy
• An ion is an atom or group of bonded atoms that
has a positive or negative charge
• Sodium (Na), for example, easily loses an
electron to form Na
• Any process that results in the formation of an
ion is referred to as ionization
• The energy required to remove one electron from a
neutral atom of an element is the ionization
energy, IE (or first ionization energy, IE1)

15
Trends and the Periodic Properties
• Ionization Energy
• In general, ionization energies of the main-group
elements increase across each period (increasing
groups)
• This increase is caused by increasing nuclear
charge
• A higher charge more strongly attracts electrons
in the same energy level
• Among the main-group elements, ionization
energies generally decrease down the groups
(increasing periods)
• The electrons are removed more easily

16
Trends and the Periodic Properties
• Ionization Energy

17
Trends and the Periodic Properties
• Ionization Energy
• Sample Problem
• Consider two main-group elements, A and B.
Element A has a first ionization energy of 419
kJ/mol. Element B has a first ionization energy
of 1000 kJ/mol. Decide if each element is more
likely to be in the s block or p block. Which
element is more likely to form a positive ion

18
Trends and the Periodic Properties
• Ionization Energy
• Sample Problem Solution
• Element A has a very low ionization energy, which
means that atoms of A lose electrons easily
• Element A is most likely to be an s-block metal
because ionization energies increase across the
periods
• Element B has a very high ionization energy which
means that atoms of B have difficulty losing
electrons
• Element B would most likely lie at the end of a
period in the p block
• Element A is more likely to form a positive ion
because it has a much lower ionization energy
than element B does

19
Electron Affinity
• The energy change that occurs when an electron is
acquired by a neutral atom is called the atoms
electron affinity
• Electron affinity generally increases across
periods (increasing groups)
• Increasing nuclear charge along the same sublevel
attracts electrons more strongly
• Electron affinity generally decreases down groups
(increasing periods)
• The larger an atoms electron cloud is, the
farther away its outer electrons are from its
nucleus

20
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21
• A positive ion is known as a cation
• The formation of a cation by the loss of one or
more electrons always leads to a decrease in
• The electron cloud becomes smaller
• The remaining electrons are drawn closer to the
nucleus by its unbalanced positive charge
• A negative ion is known as an anion
• The formation of an anion by the addition of one
or more electrons always leads to an increase in

22
• Cationic and anionic radii decrease across a
period
• The electron cloud shrinks due to the increasing
nuclear charge acting on the electrons in the
same main energy level
• The outer electrons in both cations and anions
are in higher energy levels as one reads down a
group
• There is a gradual increase of ionic radii down a
group

23
Trends and the Periodic Properties

24
Trends and the Periodic Properties
• Valence Electrons
• The electrons available to be lost, gained, or
shared in the formation of chemical compounds are
referred to as valence electrons
• Valence electrons are often located in
incompletely filled main-energy levels

25
Electronegativity
• Electronegativity is a measure of the ability of
an atom in a chemical compound to attract
electrons from another atom in the compound
• Electronegativities tend to increase across
periods, and decrease or remain about the same
down a group

26
Trends and the Periodic Properties
• Electronegativity
• Sample Problem
• Of the elements gallium, Ga, bromine, Br, and
calcium, Ca, which has the highest
of periodic trends

27
Trends and the Periodic Properties
• Electronegativity
• Sample Problem Solution
• All of these elements are in the fourth period
• Bromine has the highest atomic number and is
farthest to the right in the period
• Bromine should have the highest electronegativity
because electronegativity increases across the
periods