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Ch 7 Notes Outline
7.1 Development of Periodic table
Mendeleev and Meyer – element arrangement
Moseley – Nuclear charge/atomic number
Regents question: What is the charge of the nucleus in Oxygen 17?
GIVE IT SOME THOUGHT
Arranging the elements by atomic weight leads to an order slightly different from that in a modern periodic table,
where the arrangement is by atomic number. Why does this happen?
Looking at the periodic table can you find an example other than Ar and K where the order of the elements would
be different if the elements were arranged in order of increasing atomic weight?
7.2 Effective nuclear charge
Properties of atoms depend on attraction… and repulsion…
Shielding effect
Effective nuclear charge
Ex: Magnesium vs. chlorine
GIVE IT SOME THOUGHT
Which would you expect to experience a greater effective nuclear charge, a 2p electron of a Ne atom or a 3s
electron of a Na atom?
7.3 Sizes of atoms and ions
bonding atomic radius –
within a period…
within a group…
Estimating bonding lengths
Ex:
Sample 7.1 Natural gas used in home heating and cooking is odorless. Because natural gas leaks pose the
danger of explosion or suffocation, various smelly substances are added to the gas to allow detection of a leak.
One such substance is methyl mercaptan, CH3SH. Use Figure 7.6 to predict the lengths of the C-S, C-H, S-H
bonds in this molecule.
Practice:
Using Figure 7.6, predict which is longer, the P-Br bond in PBr3 or the As-Cl bond in AsCl3.
GIVE IT SOME THOUGHT
In Section 7.2 we said that Zeff generally increases when you move down a column of the periodic table, whereas
in Chapter 6 we saw that the “size” of an orbital increases as the principal quantum number n increases. With
respect to atomic radii, do these trends work together or against each other? Which effect is larger?
SAMPLE 7.2 Atomic Radii
Referring to a periodic table, arrange (as much as possible) the atoms 15P, 16S, 33As, and 34Se
in order of increasing size. (Atomic numbers are given to help you locate the atoms quickly in
the table.)
Practice: Arrange 11Na, 4Be,and 12Mg in order of increasing atomic radius.
Regents questions
Trends in ion Radius
Ionic size depends on…
Cations –
Anions –
SAMPLE 7.3 Atomic and Ionic Radii
Arrange Mg2+, Ca2+ and Ca in order of decreasing radius.
PRACTICE: Which of the following atoms and ions is largest: S2-, S, or O2- ?
Isoelectronic series –
SAMPLE EXERCISE 7.4 Ionic Radii in an Isoelectronic Series
Arrange the ions K+ , Cl- , Ca2+, and S2- in order of decreasing size.
PRACTICE:
In the isoelectronic series Rb+, Sr2+, Y3+, which ion is largest?
7.4 Ionization energy
def. –
Ex: Na
Ex: Al
GIVE IT SOME THOUGHT
Light can be used to ionize atoms and ions. Which of the two processes shown in Equations 7.2 and 7.3 requires
shorter-wavelength radiation?
7.3 Na+(g)  Na2+ (g) + e7.2
Na (g)  Na+(g) + e-
SAMPLE 7.5 Trends in Ionization Energy
Three elements are indicated in the periodic table in the margin. Which one
has the largest second ionization energy?
PRACTICE: Which has the greater third ionization energy, Ca or S?
GIVE IT SOME THOUGHT
Which would you expect to be greater, I1 for a boron atom or I2 for a carbon atom?
Trends in 1st ionization energy
In a Group –
In a period –
Exceptions:
SAMPLE 7.6 Periodic Trends in Ionization Energy
Referring to a periodic table, arrange the atoms Ne, Na, P, Ar, K in order of increasing first ionization energy.
PRACTICE
Which has the lowest first ionization energy, B, Al, C, or Si? Which has the highest?
GO FIGURE: Explain why it is easier to remove a 2p electron from an oxygen atom than from a nitrogen atom.
Photo Electron Spectroscopy
Example Mg:
The diagram right is PES for a metallic element
a) Label the valence electrons.
b) Identify the above element.
c) Write the electron configuration for the atom.
Consider the PES spectra shown, that superimposes
the simulated PES spectra for boron and carbon on the same plot.
a) Suggest a reason why the boron and carbon peaks have been paired together
in three groups labeled x, y and z.
b) Explain why the carbon ‘x peak’ is at a higher energy than the boron ‘x peak’.
c) Why is the boron ‘z peak’ half the height of the carbon ‘z peak’?
d) If one were to superimpose a third PES plot on the same axes for elemental nitrogen;
(i) Relative to carbon’s ‘x peak’, where would nitrogen’s ‘x peak’ appear on the x-axis? Explain.
(ii) Relative to carbon’s ‘z peak’, what would the height of nitrogen’s ‘z
peak’, be? Explain.
(e) Identify the electrons that are associated with each peak in the boron plot.
(i) boron ‘x peak’
(ii) boron ‘y peak’
(iii) boron ‘z peak’
Electron configurations of ions
The rule:
Ex:
GIVE IT SOME THOUGHT
Do Cr 3+ and V 2+ have the same or different electron configurations?
SAMPLE 7.7 Electron Configurations of Ions
Write the electron configuration for (a) Ca2+
, (b) Co3+ and (c) S2-
PRACTICE
Write the electron configuration for (a) Ga3+
, (b) Cr3+ ,and (c) Br-
.
7.5 Electron Affinity
def. –
ex: Chlorine
Trends:
Exceptions:
GO FIGURE
Which of the groups shown here has the most negative electron
affinities? Why does this make sense?
GIVE IT SOME THOUGHT
What is the relationship between the value for the first ionization energy of a Cl- ion and the electron affinity of
Cl(g)?
Regents Reference table S information
Regents questions:
7.6 metals, nonmetals, metalloids
Metal properties:
Metallic character –
Go figure – Notice that germanium, Ge is a metalloid but tin, Sn, is a metal. What changes in atomic properties do
you think are important in explaining this difference?
Give it some thought – Describe the relationship between the trends in metallic character and trends in ionization
energy:
Metals vs. Nonmetals
Reactions of metals with nonmetals
Metals act like….
Soluble metal oxides in water -
Insoluble metal oxides in acids
Sample 7.8
a) Would you expect scandium oxide to be a solid, liquid or gas at room temperature?
b) Write the balanced equation for scandium oxide with nitric acid
Practice: write the balanced chemical equation for the reaction between copper (II) oxide and sulfuric acid:
Nonmetals
Properties
Form molecular compounds
Nonmetals act like….
Nonmetal oxides in water -
Nonmetal oxides with bases –
Sample 7.9 – Write the balanced chemical equation for the reaction of solid selenium dioxide , SeO 2 with …
a) water
b) aqueous sodium hydroxide
Practice – write the balanced chemical equation for the reaction of solid tetraphosphorus hexoxide with water
Give it some thought- A compound ACl3 has a melting point of –112 dC. Would you expect the compound to be
molecular or ionic? If you were told that A is either scandium or phosphorus, which do you think is the more likely
choice?
Metalloids
7.7 Group Trends:
1A alkali metals
Properties
Reactions:
Give it some thought: Cesium tends to be the most reactive of the stable alkali metals. What atomic property of
Cs is most responsible for its high reactivity?
Sample 7.10 – Reactions of an alkali metal
Write the balance equation for the reaction of cesium metal with
a) Cl2
b) H2O
c) H2
Practice: write the balanced equation for the reaction between potassium metal and elemental sulfur:
2A Alkaline earth metals
Properties –
Reactions
Give it some thought: calcium carbonate CaCO3 is often used as a dietary calcium supplement or bone health,
although CaCO3 is insoluble in water. It can be taken orally to allow for the delivery of Ca2+ ions to the
musculoskeletal system. Why is this the case? Write the equation to illustrate:
7.8 Nonmetals
Properties
Hydrogen
Group 6A
Oxygen
Give it some thought: hydrogen peroxide is light sensitive and so is stored in brown bottles because its O-O bond
is weak. If we assume that the brown bottle absorbs all visible wavelengths of light, how might you estimate the
energy of the bond in hydrogen peroxide? (Hint: visible lights wavelength varies from 400 nm to 750 nm)
Sulfur
Group VIIA: halogens
Properties
Reactions:
Fluorine:
Chlorine:
Group VIIIA Noble gases:
Sample Exercise: The element bismuth is the heaviest member of group 5A. A salt of the element bismuth
subsalicylate, is the active ingredient in pepto-bismol.
a) the bonding radii of thallium and lead are 1.48 A and 1.47 A respectively. Using these values and figure 7.6,
predict the bonding atomic radius of t element Bi. Justify your response
b) What accounts for the general increase in atomic radius going down group 5A elements?
c) Another major use of Bi has been in low mp alloys as those in fire sprinkler systems. The element itself is a
brittle crystalline solid. How do these characteristics fit with th efact that Bi is in the same group with nonmetals
like N and P?
d) Bi2O3 is a basic oxide. Write the balanced equation for its reaction with dilute nitric acid:
if 6.77g of Bi2O3 is dissolved in dilute acid solution to make 0.500 L of solution, what is the molarity of the Bi3+ ion?
e) Bi209 is the heaviest stable isotope of any element. How many protons, and neutrons are present in this
nucleus?
f) the density of Bi at 25 dC is 9.808 g/cm 3 . How many Bi atoms are present in a cube of the element that is 5.00
cm on each edge? How many moles of the element are present?