The Periodic Law - PowerPoint PPT Presentation

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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
Atomic Radii
  • 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
  • Atomic Radii
  • 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
  • Atomic Radii

11
Trends and the Periodic Properties
  • Atomic Radii

12
Trends and the Periodic Properties
  • Atomic Radii
  • Sample Problem
  • Of the elements magnesium, Mg, chlorine, Cl,
    sodium, Na, and phosphorus, P, which has the
    largest atomic radius? Explain your answer in
    terms of trends of the periodic table

13
Trends and the Periodic Properties
  • Atomic Radii
  • 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
Ionic Radii
  • 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
    atomic radius
  • 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
    atomic radius

22
Ionic Radii
  • 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
  • Ionic Radii

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
    electronegativity? Explain your answer in terms
    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
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