Download AtomsFirst2e_day4_sec2.3-2.6

2.3 Atomic Number, Mass Number, and Isotopes
All atoms can be identified by the number of protons and neutrons
they contain.
The atomic number (Z) is the number of protons in the nucleus.
 Protons determine the identity of an element. For example,
nitrogen’s atomic number is 7, so every nitrogen has 7 protons.
The mass number (A) is the total number of protons and neutrons.
 Protons and neutrons are collectively referred to as nucleons.
Mass number
(number of protons + neutrons)
Atomic number
(number of protons)
A
Z
X
Elemental symbol
Atomic Number, Mass Number, and Isotopes
Most elements have two or more isotopes, atoms that have the
same atomic number (Z) but different mass numbers (A).
1 proton
0 neutrons
1 proton
1 neutron
1 proton
2 neutrons
Isotopes of the same element exhibit similar chemical properties,
forming the same types of compounds and displaying similar
reactivities.
2.4
Nuclear Stability
The number of protons and
neutrons present in an
atom determine the
stability of the nucleus –
will discuss in detail in
chapter 20 (CHMY 172)
3
2.5 Average Atomic Mass
Atomic mass is the mass of an atom in atomic mass units (amu).
1 amu = 1/12 the mass of a carbon-12 atom
The average atomic mass on the periodic table represents the
average mass of the naturally occurring mixture of isotopes.
Isotope
Isotopic mass (amu)
Natural
abundance (%)
12C
12.00000
98.93
13C
13.003355
1.07
Average mass (C) = (0.9893)(12.00000 amu) + (0.0107)(13.003355 amu)
= 12.01 amu
Which isotope has a greater abundance naturally, bromine-79 or bromine-81?
Average Atomic Mass
Measuring Atomic Mass
 The most direct and
most accurate method
for determining
atomic and molecular
masses is mass
spectrometry, using a
mass spectrometer.
 The mass spectrum
of neon
Worked Example 2.1
Determine the numbers of protons, neutrons, and electrons in each of the
35
41
37
following species: (a) 17 Cl, (b) Cl, (c) K, and (d) carbon-14.
Strategy Recall the superscript denotes the mass number (A) and the subscript
denotes the atomic number (Z). If no subscript is shown, the atomic number can
be deduced from the elemental symbol or name. There is no charge shown on
these atoms.
• https://phet.colorado.edu/en/simulation/build-an-atom
Text Practice: 2.14 2.18 a)
2.6 The Periodic Table
The periodic table is a chart in which elements having similar
chemical and physical properties are grouped together.
The Periodic Table
Elements are arranged in periods, horizontal rows, in order of
increasing atomic number.
The Periodic Table
Elements can be categorized as metals, nonmetals, or metalloids.
Metals are good conductors
of heat and electricity.
Nonmetals are poor
conductors of heat or
electricity.
Metalloids have
intermediate properties.
The Periodic Table
A vertical column is known as a group.
The Periodic Table
Group 1A elements (Li, Na, K, Rb, Cs, Fr) are called alkali metals.
The Periodic Table
Group 2A elements (Be, Mg, Ca, Sr, Ba, Ra) are called alkaline
earth metals.
The Periodic Table
Group 6A elements (O, S, Se, Te, Po) are called chalcogens.
The Periodic Table
Group 7A elements (F, Cl, Br, I, At) are called halogens.
The Periodic Table
Group 8A elements (He, Ne, Ar, Kr, Xe, Rn) are called the noble
gases.
The Periodic Table
Groups 1B and 3B-8B are called the transition elements or
transition metals.
Chemistry: Atoms First
Second Edition
Julia Burdge & Jason Overby
Chapter 3
Quantum Theory and
the Electronic
Structure of Atoms
M. Stacey Thomson
Pasco-Hernando State College
Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
3.1
Energy and Energy Changes
Energy is the capacity to do work or transfer heat.
Energy is either kinetic or potential.
Kinetic energy (Ek) is the energy of motion.
 m is the mass of the object
 u is its velocity
One form of kinetic energy of particular interest to chemists is
thermal energy, which is the energy associated with the random
motion of atoms and molecules.
Forms of Energy
Potential energy is the energy possessed by an object by virtue of its
position or stability.
There are two forms of potential energy of great interest to chemists:
 Chemical energy is energy stored within the structural units of
chemical substances.
 Electrostatic energy is potential energy that results from the
interaction of charged particles.
Q1 and Q2 represent two charges separated by the distance, d.
Energy and Energy Changes
Kinetic and potential energy are interconvertible – one can be
converted to the other.
Although energy can assume many forms, the total energy of the
universe is constant.
 Energy can neither be created nor destroyed.
 When energy of one form disappears, the same amount of
energy reappears in another form or forms.
 This is known as the law of conservation of energy.
• http://mw.concord.org/modeler/showcase/simulation.html?s=http://mw2.concor
d.org/public/part2/heat/index.html (activities 2-7)
Text Practice: 3.4
Units of Energy
The SI unit of energy is the joule (J), named for the English
physicist James Joule.
It is the amount of energy possessed by a 2-kg mass moving at a
speed of 1 m/s.
Ek = ½ mu2 = ½(2 kg)(1 m/s)2 = 1 kg∙m2/s2 = 1 J
The joule can also be defined as the amount of energy exerted
when a force of 1 newton (N) is applied over a distance of 1 meter.
1J=1N·m
Because the magnitude of a joule is so small, we often express
large amounts of energy using the unit kilojoule (kJ).
1 kJ = 1000 J
Study Guide for sections 2.3-2.6, 3.1
DAY 4, Terms to know:
Sections 2.3-2.6, 3.1 atomic number, mass number, isotope, average mass,
isotopic natural abundance, periodic table, halogens, noble gasses, transition
metals, energy, kinetic energy, thermal energy, potential energy, chemical energy,
electrostatic energy, law of conservation of energy, joule
DAY 4, Specific outcomes and skills that may be tested on exam 1:
Sections 2.3-2.6, 3.1
•Be able to use elemental symbols to determine how many protons, neutrons, and
electrons are present in an atom
•Given a specific number of protons, neutrons, and electrons, be able to give a
complete elemental symbol including element, mass, and charge
•Given isotopes and their natural abundance, be able to calculate the average
atomic mass
•Given an average atomic mass and two or three isotopes, be able to describe the
isotopes relative abundances
•Be able to describe possible transformations from one form of energy to another
•Given a process that involve a transfer of energy, be able to describe to describe
what forms of energy exist before and after the process
Extra Practice Problems for sections 2.3-2.6, 3.1
Complete these problems outside of class until you are confident you have learned
the SKILLS in this section outlined on the study guide and we will review some of
them next class period. 2.15 2.17 2.19 2.21 2.35 2.67 2.69 2.79 2.81
Prep for day 5
Must watch videos:
http://echem1a.cchem.berkeley.edu/modules/module-2 (UC-Berkeley watch lessons 3-6: light and
matter, particles and waves)
Other helpful videos:
http://ocw.mit.edu/courses/chemistry/5-111-principles-of-chemical-science-fall-2008/video-lectures/
(MIT lectures 4 and 5)
http://ps.uci.edu/content/chem-1a-general-chemistry (UC-Irvine lectures 3-5)
Read sections: 3.2-3.6