 # Chapter 2: Atoms, Molecules and Ions. Dr. PÃ©rez

```Dr. Pérez
CHM1045 Chapter 2
pg 1 of 11
(1) Chapter 2: Atoms, Molecules and Ions
Learning Goals
• Brief basis of our modern atomic theory
• Understand laws of
• conservation of mass
• definite proportion
• multiple proportions
• Know mass and charge of subatomic particles
• Write isotopic symbols
• Determine p+, no, e-, Z, and A from isotopic symbol
• Understand / calculate atomic weight
• Predict charge of ions
• Convert between moles and number of atoms
• Convert between moles and mass
(2) Modern Atomic Theory
Atom - ______________ ______________ of an ______________ that retains the
______________ properties of that ______________
The atoms of an element are ______________ from the atoms of another element
Atomic


Theory
all matter is made of ______________
compounds are composed of atoms of two or more ______________ chemically
combined in fixed proportions (law of definite proportion or constant composition)
Nuclear
Model of the Atom

nucleus - ______________ & ______________

electrons - ______________ the ______________
(3) Learning Check The composition of a sample was determined in triplicate. Results:
#
1
2
3
mass sample
103 g
75 g
144 g
mass Cu
53 g
28 g
79 g
mass C
10. g
14 g
38 g
mass O
40. g
33 g
28 g
The sample is a (law that allowed you to determine this)
A.
pure substance (law of conservation of mass)
B.
pure substance (law of definite proportions)
C.
mixture (law of conservation of mass)
D.
mixture (law of definite proportions)
Dr. Pérez
CHM1045 Chapter 2
pg 2 of 11
(4) Law of Multiple Proportions
When two elements (call them A and B) form two different compounds, the masses of
element B that combine with 1 g of element A can be expressed as a ratio of small whole
numbers.
• Result: Mass ratios are small, whole-number multiples of each other
Exercise: Nitrogen monoxide and nitrogen dioxide are both gases that contain only
nitrogen and oxygen. A sample of nitrogen monoxide contains 1.00 g of N and 1.14 g
of O. A sample of nitrogen dioxide contains 1.00 g of N and 2.28 g of O. Show that
the two obey the law of multiple proportions.
EOCE: 2.29, 2.31, 2.33, 2.35, 2.37
(5) 2.6 Subatomic Particles
“Chemistry, A Molecular Approach”, Tro, 2014
amu ______________________________________________________
1 amu = 1.66053873 x 10-27 kg
Dr. Pérez
CHM1045 Chapter 2
pg 3 of 11
(6) Atoms and Isotopic Symbols
Properties of atoms depend on the number of ____________, ____________ and
____________ it has.

Atomic number –

Mass number –

Isotopes –

Isotopic symbol -
(7) Isotopic Symbols Exercise
1. Complete the table:
Nuclide
# p+
95
# no
# e-
Cd
48
56
Ni
28
Al3+
36 “
X”
16
17 “
X”2-
8
2.
Which are isotopes? Identify the elements.
EOCE 2.47, 2.51, 2.53, 2.55, 2.57, 2.61, 2.104
Atomic #
Mass #
Dr. Pérez
CHM1045 Chapter 2
pg 4 of 11
(8) 2.7 The Periodic Table, Fig. 2.12 “Chemistry, A Molecular Approach”, Tro, 2014
(9) The Periodic Table
 Periods – __________ _____
 Group or family – _____________
o Group number AND Group name:
Dr. Pérez
CHM1045 Chapter 2
pg 5 of 11
Types of Elements
(10) Metals
 Solid elements at room temperature, except for ____________________
 Tend to be shiny
 Silvery; gray color
 ____________________melting and boiling points
 ____________________average density
 ____________________conductors of heat and electricity
 Malleable; ductile
 Form ____________________
(11) Non-Metals
 Lack metallic properties
 At room temperature most are gases (all of 8 A, N, O, F, Cl, H), a few solids (C,
S, P, Se, I) and one liquid (____________________)
 Poor conductors of heat and electricity
 Characteristics lower than metals

Melting and boiling points, density, electric and heat conductivities
 Usually form ____________________
(12) Metalloids or Semimetals
 Have both metallic and non-metallic properties (exhibit mixed properties)
 B, Si, Ge, As, Sb, Te, At
 Most form various ions
EOCE: 2.63, 2.65, 2.67, 2.69
(13) Exercise
A. Classify as metal (M) , nonmetal (N) or metalloid (Md):
1. Lr ___
Os ___
H _____
Ge _____
2. An element that is liquid at room temperature and conducts electricity. _____
3. An element that is solid at room temperature and is a poor conductor of heat.
____
Dr. Pérez
CHM1045 Chapter 2
B. Answer true (T) or false (F) regarding nitrogen and antimony.
1. They are both nonmetals. ______
2. They are in the same group. ______
3. They are in the same period. ______
4. They are the same state. _____
C.
Family name
group number
Mg
Ga
(14) Predicting Charges
Ion charge of elements with predictable charges:
EOCE: 2.59
pg 6 of 11
period
Dr. Pérez
CHM1045 Chapter 2
pg 7 of 11
(15) 2.8. Atomic Mass (Weight) of Elements
 Most elements have several ________________.
 The atomic mass of an element is actually an average atomic mass of its isotopes
taking into _____________ their natural abundance, expressed in atomic mass
units
o included in periodic table
90.40%
10
Ne
20.18
neon
0.27% 9.25%
Mass Spectrum of Ne
Exercises:
(16) Bromine (used to make silver bromide, the important component of photographic
film) has two naturally occurring isotopes, Br-79 and Br-80. Br-79 has a mass of
78.918336 amu and a percent abundance of 50.69%. The other isotope has a mass of
80.916289 amu, and a percent abundance of 49.31%. Calculate the atomic mass of
bromine.
A. All Ga atoms weigh 69.7 amu.
B. The atomic mass of Ga is the average of 68.9
and 71.9.
C. The atomic mass of Ga will be closer to 69
than 71 because there are more atoms that
weigh 68.9 amu.
EOCE: 2.71, 2.73, 2.75, 2.77
Gallium Mass Spectrum
Relative Abundance (%)
(17) The mass spectrum of gallium, Ga, is shown as
follows. The atomic mass of Ga is 69.7 amu. Which
of the following statements is correct?
70
60
50
40
30
20
10
0
67
68
69
70
Mass (amu)
71
72
Dr. Pérez
CHM1045 Chapter 2
pg 8 of 11
(18) Section 3.8 Formula Mass of a Compound
• Formula Mass - the average mass of a molecule of a compound in amu
• a.k.a. molecular mass or molecular weight
• Sum of the atomic masses of the atoms in amu
• Exercise:
• Calculate the formula mass of 1 molecule of H2O
EOCE 3.59
(19) 2.9 & 3.8 The Mole & Avogadro
• Chemists count particles (____________, ____________, ____________,
etc.) by the mole.
•
_________ _________ - amount of substance that contains the same
number of particles as there are atoms in 12 g of ____________.
• 1 mol = __________________ particles: Avogadro’s number
(20) 6.022 x 1023




If you could travel at the speed of light, it would take you more than 100
billion years to travel 6.022 x 1023 meters
A stack of paper with 6.022 x 1023 sheets would be so tall that it would reach
from here to the sun-not just once but more than a million times
1 mole of seconds represents the span of time 4 million times as long as the
1 mole of marbles is enough to cover the entire earth to a depth of 50 miles
(21) Moles to Units and Units to Moles
• Use conversion factor
1 mol = __________ particles
1. How many moles are there in 7.95 x 1017 atoms of He?
Dr. Pérez
CHM1045 Chapter 2
2. How many moles of CO2 are there in 2.99 x 1052 molecules of CO2?
3. Calculate the number of magnesium atoms in 2.5 moles of Mg2N3.
(22) Molar Mass
 Mass, in grams, contained in 1 mole (mass of 6.022 x 1023 atoms)
 Same as the amu but in g/mol
 Example: Molar mass
Cl
_____________ ___________
Ca _____________ __________
Al(NO3)3 _____________ __________
(23) Exercise: Moles to Grams & Grams to Moles
•
Use conversion factor:
1 mol = molar mass in g
1. Calculate the mass of 5.5 mol of chromium.
2. What is the amount, in moles, of 33.5 g of potassium oxide, K2O?
pg 9 of 11
Dr. Pérez
CHM1045 Chapter 2
(24) Putting it All Together
1. What is the mass in grams of 5.6 x 1019 molecules of CO?
2. What is the mass of 1 formula unit of CaO?
3. How many atoms of H are there in 25.0 g of C6H12?
4. How many ions of Cl- are there in 7 formula units of MgCl2?
Learning Check
(25) How many atoms of oxygen are there in 100.0 g of Mg3 (PO4)2?
A. 2.291 x 1023 atoms O
B. 2.864 x 1022 atoms O
C. 1.833 x 1024 atoms O
D. 3.804 x 10-1 atoms O
pg 10 of 11
Dr. Pérez
CHM1045 Chapter 2
(26) Which has more atoms, 10.0 g Mg or 10.0 g Ca?
A. Magnesium
B. Calcium
C. Both have the same number of atoms.
(27) Which of the following has the largest mass?
A. 10.0 g Li
B. 4.5 x 1024 atoms of Li
C. 100.0 g Na
D. 9.0 moles of K
E. 2.9 x 1023 atoms Rb
EOCE: 2.81, 2.83, 2.85, 2.87, 2.89, 2.91, 3.61, 3.63, 3.65, 3.67, 3.69
pg 11 of 11
``` # Arts and Sciences Program Chemistry Department Chemistry Placement Test # John Dalton William Crookes J.J. Thomson Ernest Rutherford 