Download atom

 Think of a gift you have received. Did
you try to guess what was inside it
without opening it?
 How did you figure it out?
Scanning Electron Microscope
Atomic Structure
 4.1a Explain how Democritus and John Dalton
described atoms.
 4.1b Identify instruments used to observe individual
atoms.
 4.2a Identify three types of subatomic particles.
 4.2b Describe the structure of atoms according to the
Rutherford atomic model
 An atom is the smallest part of an element
that retains its identity in chemical
reactions
 Why do people use
models?
 What models do you
have or have you used?
 Early philosophers and
scientists developed
models of the atom to
help explain the nature
of matter
 Greek Philosopher
 First proposed the idea
of the “atom”
 No real evidence to
support his claim
 English Chemist and
Schoolteacher
 Used scientific method
to come up with
Dalton’s Atomic
Theory
 1. All elements are made of tiny indivisible particles
called atoms
 2. Atoms of the same element are identical. The atoms
of any one element are different from those of any
other element
 3. Atoms of different elements can physically mix
together or can chemically combine in simple wholenumber ratios to form compounds
 4. Chemical reactions occur when atoms are separated
from each other, joined, or rearranged in a different
combination. Atoms of one element, however, are
never changed to atoms of another element as a result
of a reaction
Atom A
Atom B
 http://learn.genetics.utah.edu/content/begin/cells/sc
ale/
 Very small
 A copper coin contains 2 x 1022 atoms
 Most atomic radii are in the range of 5 x 10-11 to 2 x 10-10
meters
 “All atoms are identical”
 FALSE- all atoms of a given element are identical
 “Chemical reactions occur when atoms of one element
change into atoms of another element”
 FALSE- atoms of one element cannot change into
another element
So, was
Dalton correct
about atoms?
 How can we see atoms?
 Electron microscopes use
high speed electrons to
see atoms
Carbon
Hydrogen
 http://www.youtube.com/watch?v=cQU2IAsQak8
 If we did the experiment that we did on Friday, but the
marble passed under the table without being deflected
most of the time, what might you conclude about the
object underneath?
 4.2a Identify three types of subatomic particles.
 4.2b Describe the structure of atoms according to the
Rutherford atomic model
 Electrons are negatively
charged subatomic
particles.
 Discovered by English
Physicist J.J. Thomson
 Cathode ray: a stream
of electrons produced at
the negative electrode
(cathode) of a tube
containing a gas at low
pressure.
 http://www.youtube.com/watch?v=2xKZRpAsWL8
 http://www.youtube.com/watch?v=O9Goyscbazk
• Measured the charge required to suspend an oil drop
• Determined mass of electron to be 9.10938291 × 10-28 grams
http://www.learnerstv.com/animation/animation.php?ani=186&cat=Chemistry
 Protons are positively
charged subatomic
particles
 Much larger than
electrons
 Discovered by Eugen
Goldstein, when he saw
that there existed
another set of particles in
a CRT traveling in the
opposite direction
 Neutrons are subatomic
particles with no charge
but have a mass nearly
equal to that of a proton
 Discovered by James
Chadwick
 Ernest Rutherford and his colleagues
performed the experiment
 http://www.youtube.com/watch?v=XBqHkraf8iE
 http://micro.magnet.fsu.edu/electromag/java/rutherf
ord/
 Where have you heard
the term “Nucleus”
before?
 The nucleus is the tiny
central core in an atom
and is composed of
protons and neutrons
 4.3a Explain what makes elements and isotopes
different from each other and how isotopes of an
element differ.
 4.3b Calculate the atomic mass of an element.
Atomic number
Mass number
 Atomic number is
 Mass number is the
equal to the number of
protons in an atom
total number of protons
and neutrons in an atom
 Unique to each element!
 Usually equal to number
of electrons as well
# of neutrons = mass number – atomic number
 Mass number is in the
197
79
Au
superscript (on top)
 Atomic number is in the
subscript (on bottom)
 How many neutrons does
gold have?
 197-79= 118
 How many electrons does
gold have?
 79
 Isotopes are atoms that
have the same number of
protons but different
numbers of neutrons
 Neon-20
 Neon-21
 Neon-22
 How many protons are
in each?
 How many neutrons
are in each?
Element
Number
of
Protons
Manganese
25
Sodium
Bromine
Number of
Electrons
Actinium
Atomic
Number
Mass
Number
39
89
30
11
35
12
45
Yttrium
Arsenic
Number of
Neutrons
33
75
227
Element
Number
of
Protons
Number of
Electrons
Number of
Neutrons
Atomic
Number
Mass
Number
Manganese
25
25
30
25
55
Sodium
11
11
12
11
23
Bromine
35
35
45
35
80
Yttrium
39
39
50
39
89
Arsenic
33
33
42
33
75
Actinium
89
89
138
89
227
 Lesson Check 4.2
 P. 122, question 51
 Finish Lab Questions from Friday
 In this class, I grade based on 50% Tests, 25% Labs,
and 25% HW.
 If you received a 70 on tests, a 93 on HW, and an 85 on
labs, what would your overall grade be?
 4.3a Explain what makes elements and isotopes
different from each other and how isotopes of an
element differ.
 4.3b Calculate the atomic mass of an element.
 The mass of atoms are very small
 Instead of referring to their actual mass in grams, we use
something more convenient
 Atomic Mass unit (amu)- one twelfth of a carbon
atom
 Same as the mass of a proton or neutron
 We use a mass number to
refer to one individual
atom.
 For an element with
many atoms, we use
atomic mass
 Weighted average mass
of the atoms in a
naturally occuring
sample of the element
 You have a sample of carbon that contains 98.89% carbon-
12 (12 amu), and 1.11% carbon-13 (13 amu). What is the
atomic mass?
 Weighted average
 Atomic mass = (12.00 amu x 0.9889) + (13.00 amu x 0.011)


= (11.867 amu) + (0.144 amu)
= 12.011 amu
 An element “X” has four major isotopes, which are
listed below along with their abundances. Calculate
the average atomic mass. What is the element?
Isotope
Mass
Percent
Abundance
46X
45.952630
8.25
47X
46.951764
7.44
48X
48.947947
73.73
49X
48.947871
?
 Complete Vegium Lab
 Quiz tomorrow
 Test Friday