Download AtomsFirst2e_day3_sec1.6_2.1-2.2

1.6
Using Units and Solving Problems
A conversion factor is a fraction in which the same quantity is
expressed one way in the numerator and another way in the
denominator.
For example, 1 in = 2.54 cm, may be written:
1 in
2.54 cm
or
2.54 cm
1 in
Dimensional Analysis – Tracking Units
The use of conversion factors in problem solving is called
dimensional analysis or the factor-label method.
 Example: Convert 12.00 inches to meters.
12.00 in ×
= 30.48 cm
Which conversion factor will cancel inches and give us centimeters?
1 in
2.54 cm
or
Convert 4.35 x 10-4 kiloliters to microliters
Text Practice: 1.50 b d
2.54 cm
1 in
Worked Example 1.8
An average adult has 5.2 L of blood. What is the volume of blood in cubic
meters?
Strategy 1 L = 1000 cm3 and 1 cm = 1x10-2 m. When a unit is raised to a
power, the corresponding conversion factor must also be raised to that power in
order for the units to cancel appropriately.
Worked Example 1.3
Ice cubes float in a glass of water because solid water is less dense than liquid
water. (a) Calculate the density of ice given that, at 0°C, a cube that is 2.0 cm on
each side has a mass of 7.36 g, and (b) determine the volume occupied by 23 g of
ice at 0°C.
Text practice: 1.24 1.28 1.68
Chemistry: Atoms First
Second Edition
Julia Burdge & Jason Overby
Chapter 2
Atoms and the
Periodic Table
M. Stacey Thomson
Pasco-Hernando State College
Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
2.1
Atoms First
An atom contains specific particles. The arrangement of subatomic
particles determine the properties of atoms, which in turn determine
the properties of all matter.
An atom must contain at least 1 proton.
The elements are defined by how many protons they have.
Examples: gold, oxygen, helium
We are going to discuss how just a few of the experiments scientists
used to elucidate how atoms are composed.
2.2 Subatomic Particles and Atomic Structure
In the late 1800’s, many scientists were doing research involving
radiation, the emission and transmission of energy in the form of
waves.
They commonly used a cathode ray tube, which consists of two
metal plates sealed inside a glass tube from which most of the air
has been evacuated.
Subatomic Particles and Atomic Structure
When metal plates are connected to a high-voltage source, the
negatively charged plate, or cathode, emits an invisible ray.
The cathode ray is drawn to the anode where it passes through a
small hole.
Although invisible, the path is revealed when the ray strikes a
phosphor-coated surface producing a bright light.
• http://highered.mcgrawhill.com/sites/0073511161/student_view0/chapter2/animations.html#
• https://phet.colorado.edu/en/simulation/balloons
Subatomic Particles and Atomic Structure
This prompted him to propose the rays were actually a stream of
negatively charged particles.
These negatively charged particles are called electrons.
By varying the electric field and measuring the degree of
deflection of cathode rays, Thomson determined the charge-tomass ratio of electrons to be 1.76×108 C/g. (C is coulomb, the
derived SI unit of electric charge.)
Subatomic Particles and Atomic Structure
Wilhelm Rontgen (1845-1923) discovered X-rays. They were not
deflected by magnetic or electric fields, so they could not consist of
charged particles.
Subatomic Particles and Atomic Structure
Antoine Becquerel (1852-1908)
discovered radioactivity, the
spontaneous emission of
radiation.
Radioactive substances, such as
uranium, produce three common
types of radiation.
Alpha (α) rays consist of positively charged particles, called α
particles.
Beta (β) rays, or β particles, are electrons so they are deflected away
from the negatively charged plate.
Gamma (γ) rays, like X-rays, have no charge and are unaffected by
external electric or magnetic fields.
Subatomic Particles and Atomic Structure
• Ernest Rutherford used α
particles to prove the
structure of atoms.
• The majority of particles
penetrated the gold foil
undeflected.
• Sometimes, α particles were
deflected at a large angle.
• Sometimes, α particles
bounced back in the
direction from which they
had come.
• https://phet.colorado.edu/en/simulation/rutherfordscattering
• Activity: Propose rational for WHY gold was used and
WHY alpha particles were used in this experiment and
Subatomic Particles and Atomic Structure
Rutherford proposed a new
model for the atom:
Positive charge is concentrated
in the nucleus.
The nucleus accounts for most
of an atom’s mass and is an
extremely dense central core
within the atom.
 A typical atomic radius is about
100 pm
 A typical nucleus has a radius of
about 5×10–3 pm
 1 pm = 1×10–12 m
Subatomic Particles and Atomic Structure
Protons are positively
charged particles found in the
nucleus.
Neutrons are electronically
neutral particles found in the
nucleus.
Neutrons are slightly larger
than protons.
Text Practice: 2.8
Study Guide for sections 1.6, 2.1-2.2
DAY 3, Terms to know:
Sections 1.6, 2.1-2.2 conversion factor, dimensional analysis or factor label, atom,
element, radiation, cathode ray tube, cathode, anode, electron, alpha rays, beta
rays, gamma rays, x-rays, protons, neutrons
DAY 3, Specific outcomes and skills that may be tested on exam 1:
Sections 1.6, 2.1-2.2
•Depending on given data, be able to calculate density or use density to calculate
mass or volume
•Be able to use dimensional analysis (factor label method) to do unit conversions
using any of the units discussed or any relationships given in the problem
•Be able to describe what a cathode ray tube is and how that gives information
about atomic structure
•Be able to describe how measurements of alpha, beta, and gamma rays gave
information about atomic structure
•Be able to describe how the Rutherford gold experiment gave information about
atomic structure
Extra Practice Problems for sections 1.6, 2.1-2.2
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. 1.23 1.27 1.51 1.55 1.59 1.61 1.63 1.65 1.75 1.77
1.85 1.95 2.9
Prep for day 4
Must Watch videos:
http://www.youtube.com/watch?v=m15DWkkGe_0 (Tyler DeWitt: mass number vs. atomic mass )
https://www.youtube.com/watch?v=EboWeWmh5Pg (Tyler DeWitt: isotopes)
https://www.youtube.com/watch?v=GqtUWyDR1fg (watch first 4:46 minutes, crash course chemistry:
forms of energy)
Other helpful videos:
https://www.youtube.com/watch?v=j3FhsLbCJts&list=PLqOZ6FD_RQ7k3kp5B4jQbIA99gh73RFsh
(UC-Irvine)
https://www.youtube.com/watch?v=njGz69B_pUg (Bozeman: atomic structure and history)
http://ocw.mit.edu/courses/chemistry/5-111-principles-of-chemical-science-fall-2008/video-lectures/
(MIT lecture 3)
Read sections 2.3-2.6, 3.1