Download A mole - MSE125

Recitation_1
Chapter 2
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Q1.
(a) How many grams are there in one amu of a material?
(b) Mole, in the context of this book, is taken in units of grammole. On this basis, how many atoms are there in a gram-mole
of a substance?
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The Mole
A mole is defined as the quantity of matter that contains as many objects
(atoms, molecules, or whatever objects we are considering) as the number of
atoms in exactly 12 g of 12C. The number of atoms in a 12 g of sample of 12C to
be 6.0221421x1023 which is named as Avogadro's number (which has a symbol
of NA).
1 mol 12C atoms = 6.02 x1023 12C atoms
1 mol H2O molecules = 6.02 x 1023 H2O molecules
1 mol NO3- ions = 6.02 x 1023 NO3- ions
Molar mass is the mass in grams of one mole of a substance. The molar mass
(in grams) of any substance is always numerically equal to its formula weight
(in amu):
One 12C atom weighs 12 amu = 1 mol 12C weighs 12 g
One 24Mg atom weighs 24 amu = 1 mol 24Mg weighs 24 g
One H20 molecule weighs 18.0 amu = 1 mol H20 weighs 18.0 g
One NO3- ions weighs 62.0 amu = 1 mol NO3- ions weighs 62.0 g
Q.2
(a) Cite two important quantum mechanical concepts associated
with the Bohr model of the atom.
(b) Cite two important additional refinements that resulted from
the wave-mechanical atomic model.
Q3.
Give the electron configurations for the following ions:
Fe2+, Fe3+, Al3+, Cu+, Ba2+, Br−, O2− and S2-.
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Atomic number
91.224
Atomic symbol
Atomic weight
Zr
- Elements on the left side and in the
middle of the periodic table (except for
hydrogen) are metallic elements or
metals.
- Nonmetals are separated from metals.
- Metalloids exist between metals and
nonmetals.
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Electron Configurations and the
Periodic Table
Atom
Expected Electron
Configuration
Experimental Electron
Configuration
24Cr
1s2 2s2 2p6 3s2 3p6 4s2 3d4 1s2 2s2 2p6 3s2 3p6 4s1 3d5
29Cu
1s2 2s2 2p6 3s2 3p6 4s2 3d9 1s2 2s2 2p6 3s2 3p6 4s1 3d10
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Q4. Without consulting Periodic Table, determine whether each of the electron
configurations given below is an below is an inert gas, a halogen, an alkali metal,
an alkaline earth metal, or a transition metal. Justify your choices.
(a) 1s2 2s2 2p6 3s2 3p6 3d7 4s2
(b) 1s2 2s2 2p6 3s2 3p6
(c) 1s2 2s2 2p5
(d) 1s2 2s2 2p6 3s2
(e) 1s2 2s2 2p6 3s2 3p6 3d2 4s2
(f) 1s2 2s2 2p6 3s2 3p6 4s1
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Electron Configurations and the
Periodic Table
• Elements in any given group in the
periodic table have the same type of
electron arrangements in their
outermost shells.
• The outer shell electrons those that
lie outside the orbitals occupied in
the next lowest noble gas element
are called its valence electrons,
whereas the electrons in the inner
shells are called the core electrons.
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Electron Configurations and the
Periodic Table
The periodic table is partitioned in to different elements based on their
electron configurations.
Block diagram of the periodic table showing the groupings of the elements according to the
type of orbital being filled with electrons.
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Q5.
(a) Briefly cite the main differences between ionic, covalent,
and metallic bonding. (b) State the Pauli exclusion principle.
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Q6.
Determine the number of covalent bonds that are possible for atoms
of the following elements: germanium, phosphorus, selenium, and
chlorine.
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Q7.
Compute the percent ionic character of the interatomic bonds for
TiO2 compound.
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Electronegativity
- Tells us whether a given bond will be nonpolar covalent, polar covalent or ionic.
- The ability of an atom in a molecule to attract electrons to itself.
- Ranges from 0.7 to 4.0.
Smaller electronegativity
Larger electronegativity
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Q8.
(a) What type(s) of bonding would be expected for each of the following
materials: brass (a copper-zinc alloy), rubber, barium sulfide (BaS), bronze (a
copper-tin alloy), nylon, and aluminum phosphide (AlP)?
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