Review Problem Set 1
Plan for this week’s lab
• Lab syllabus, then sign agreement
• Check in with your lab partner
• Safety video
Tuesday, IC 420Section E: 9:00 am, Section F: 1:00 pm
Ch 2. Atoms and Elements
Substances are composed of extremely small particles called atoms.
If, in some cataclysm, all of scientific knowledge were to be destroyed, and only one sentence passed on to the next generations of creatures, what statement would contain the most information in the fewest words? I believe it is the atomic hypothesis (or the atomic fact, or whatever you wish to call it) that all things are made of atoms—little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another.
Richard Feynman
Atom
Nucleus (Rutherford’s experiment)
Electrons (Thomson’s experiment)
Atomic Nucleus
Nucleus carries positive charges
Each electron carries one negative charge
Nucleus carries almost all the mass of an atom
Atom
Nucleus
Electrons (each carries a negative charge)
Protons (each carries a positive charge)
Neutrons (neutral)
number of electrons = number of protons
= atomic number
Atoms are neutral
Atoms that have the same number of protons belong to
one kind of element.
isotopes: same number of protons, different number of neutrons
mass of a proton ≈ mass of a neutron >> mass of an electron
number of protons + number of neutrons = mass number
OR
Practice – Complete the table
Al2713
Practice – Complete the table
Al2713
C136
Mo9642
Cs13355
No change occurs inside a nucleus in chemistry
Atoms can lose or gain electrons
Na − e− → Na+ positive ion = cation
Cl + e− → Cl− negative ion = anion
Mg − 2e− → Mg2+
O + 2e− → O2−
Practice – Complete the table
3Al
Practice – Complete the table
2Mg
2S
Br
3Al
isotopes: same number of protons, different number of neutrons
mass of a proton ≈ mass of a neutron >> mass of an electron
number of protons + number of neutrons = mass number
1H 1.6735 x 10−24 g
16O 2.6560 x 10−23 g
One atomic mass unit (amu) is defined as 1/12 ofthe mass of a 12C atom.
12C atom: 6 protons, 6 neutrons, 6 electrons.
1 amu = 1.6605 x 10−24 g
1H 1.6735 x 10−24 g
16O 2.6560 x 10−23 g
1 amu = 1.6605 x 10−24 g
2424
1 amu1.6735 10 g 1.0078 amu
1.6605 10 g
2324
1 amu2.6560 10 g 15.995 amu
1.6605 10 g
23
Mass Spectrometer
Tro: Chemistry: A Molecular Approach, 2/e
Mass Spectrum of Natural Copper
69.09 % 63Cu
30.91 % 65Cu
natural abundance:percent of an isotopein nature
Mass Spectrum of Natural Copper
69.09 % 63Cu: 62.93 amu
30.91 % 65Cu: 64.93 amu
Average atomic mass of Cu = ?
How to find the average?
1, 1, 1, 1, 2
Average = (1 + 1 + 1 + 1 + 2) / 5 = 1.2
2.1
4.08.0
2%201%80
25
11
5
45
2114
5
21111
Mass Spectrum of Natural Copper
69.09 % 63Cu: 62.93 amu
30.91 % 65Cu: 64.93 amu
Average atomic mass of Cu = ?
63.55 amu
listed in the periodic table
35Cl 34.967 amu 75.78 %
37Cl 36.966 amu 24.22 %
Average atomic mass of Cl
= 34.967 amu x 75.78 % + 36.966 amu x 24.22 %
= 35.45 amu
listed in the periodic table
mass of a proton ≈ mass of a neutron ≈ 1 amu
mass number of an isotope ≈ atomic mass of the isotope in amu
35Cl 34.967 amu
37Cl 36.966 amu
One atomic mass unit (amu) is defined as 1/12 ofthe mass of a 12C atom.
The number of carbon atoms in exactly 12 g of 12Cis called Avogadro’s number: 6.022 x 1023
One Avogadro’s number of particles is called a mole.
1 mol = 6.022 x 1023 particles
1 pair = 2 particles 1 dozen = 12 particles
(exact number)
Example 2.6
Calculate the number of atoms in 2.45 mol of Cu.
1 mol = 6.022 x 1023 particles
For Practice 2.6
A pure Ag ring contains 2.80 x 1022 Ag atoms. How many moles of Ag atoms does it contain?
1 mol = 6.022 x 1023 particles
Experiment 2 next Tuesday
Read the lab manual before coming.
Bring lab manual, data form, and goggles.
Dress properly according to the syllabus.
Aprons not required for this experiment.
For an element A, its atomic mass is x amu.
What is the mass of 1 mol of A in grams?
The mass of 1 mol of A is x g.
The molar mass of an element is the mass in grams per mole of the element.
Unit: g/mol
moles
grams in massmassmolar
From the definition of molar mass:
(recall d = m/V)
1 mol = 6.022 x 1023 particles
moles
grams in massmassmolar
Unit: g/mol
molar mass and Avogadro’s number are exact numbers
By using these two equations, we can
(1) Find the number of atoms of an element from its mass.
A piece of Cu has a mass of 200. g. How many Cu
atoms are present?
1 mol = 6.022 x 1023 particles
mass in gramsmolar mass
moles
A silicon chip has a mass of 5.68 mg. How many silicon
atoms are present in the chip?
1 mol = 6.022 x 1023 particles
mass in gramsmolar mass
moles
By using these two equations, we can
(1) Find the number of atoms of an element from its mass.
(2) Find the mass of a number of atoms in grams.
Compute the mass in grams of a sample of six
mercury atoms.
1 mol = 6.022 x 1023 particles
mass in gramsmolar mass
moles
Calculate the mass of a sample of cobalt (Co) containing
5.00 x 1020 atoms.
1 mol = 6.022 x 1023 particles
mass in gramsmolar mass
moles
By using these two equations, we can
(1) Find the number of atoms of an element from its mass.
(2) Find the mass of a number of atoms in grams.
(3) Identify an element.
The mass of 500 atoms of an element is 2.24 x 10−20 g.
Identify this element.
1 mol = 6.022 x 1023 particles
mass in gramsmolar mass
moles
Problem Set 2
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