Download Honors Chemistry

Survey
yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Document related concepts

History of molecular theory wikipedia, lookup

Unbinilium wikipedia, lookup

Ununennium wikipedia, lookup

Extended periodic table wikipedia, lookup

Tennessine wikipedia, lookup

Periodic table wikipedia, lookup

Chemical element wikipedia, lookup

Isotope wikipedia, lookup

Transcript
Atoms and Elements
Mr. Matthew Totaro
Legacy High School
Honors Chemistry
Experiencing Atoms
• Atoms are incredibly small, yet they compose everything.
• Atoms are the pieces of elements.
• Properties of the atoms determine the properties of the
elements.
2
Experiencing Atoms
• There are about 91 elements found in nature.
Over 20 have been made in laboratories.
• Each has its own, unique kind of atom.
They have different structures.
Therefore they have different properties.
3
Early Theories of Matter
• The ancient Greeks
believed that all matter
was composed of only
four elements: earth,
air, water, and fire.
4
Ancient Greek Theory of Matter
Four Elements of the Ancient Greeks
5
First Atomic Theory
• Democritus (c.a. 460
BC) was the first
thinker ever to reason
that matter was not
infinitely divisible.
• He called the smallest
piece of matter
‘atomon’, which in
Greek means ‘not
cutable’.
Democritus
6
The Ancient Greeks
• Aristotle (c.a. 380
BC) reasoned,
however, that matter
was infinitely divisible.
• Aristotle’s ideas
agreed more closely
with those of the
Christian church,
therefore, they were
accepted as fact for
over two millenia.
Aristotle
Enlightenment Thinking
• Robert Boyle (c.a.
Robert Boyle
1661) wrote a book
entitled The Sceptical
Chymist. In it, Boyle
argues that the four
classical elements of the
Greeks were actually
not elements at all.
• He also argued that
matter was composed of
indivisible particles or
atoms.
8
The First Modern Atomic Theory
• After two hundred years
of experimental results,
the first modern atomic
theory was developed by
John Dalton (c.a. 1805).
• Dalton reasoned that
indivisible, spherical
particles made up all of
matter. He also argued
that these particles were
rearranged during a
chemical reaction.
John Dalton
9
Dalton’s Original Theory of the
Atom and of Reactions
10
Dalton’s Atomic Theory
1. Each Element is composed of tiny, indestructible
particles called atoms.
 Tiny, hard, indivisible, spheres.
2. All atoms of an element are identical.
 They have the same mass, volume, and other physical
and chemical properties.
 So, atoms of different elements are different.
 Every carbon atom is identical to every other carbon
atom.

They have the same chemical and physical properties.
 However, carbon atoms are different from sulfur atoms.

They have different chemical and physical properties.
11
Dalton’s Atomic Theory
3. Atoms combine in simple, whole-number
ratios to form molecules of compounds.
 Because atoms are unbreakable, they must
combine as whole atoms.
 The nature of the atom determines the ratios
in which it combines.
 Each molecule of a compound contains the
exact same types and numbers of atoms.
 Chemical formulas
12
Discovery of the Subatomic Particles
• J. J. Thomson (c.a.
1897) performed
experiments involving
cathode rays that
proved that atoms could
be broken down into
smaller particles.
• Thompson called the
particle that he
discovered an ‘electron’,
which means unit of
electricity in Greek.
J. J. Thomson
13
Cathode Ray Tube (Discovery of the
Electron)
14
Thomson’s Results
• the cathode rays are made of tiny particles
• these particles have a negative charge
because the beam always deflected toward the +
plate
• the amount of deflection was related to two factors,
the charge and mass of the particles
• every material tested contained these same particles
• Thomson called these particles ‘electrons’, because
they were the components of all electricity
15
Some Notes on Charges
• There are two kinds of
charges, called positive and
negative.
• Opposite charges attract.
 + attracted to –.
• Like charges repel.
 + repels +.
 – repels –.
• To be neutral, something
must have no charge or
equal amounts of opposite
charges.
16
Thomson’s Plum Pudding Atom
• the structure of the atom contains
many negatively charged electrons
• these electrons are held in the atom
by their attraction for a positively
charged electric field within the atom
 there had to be a source of positive
charge because the atom is neutral
 Thomson assumed there were no
positively charged pieces because none
showed up in the cathode ray experiment
17
Predictions of the Plum Pudding Atom
• the mass of the atom is due to the mass of the
electrons within it
electrons are the only particles in Plum Pudding
atoms
• the atom is mostly empty space
cannot have a bunch of negatively charged
particles near each other as they would repel
18
Radioactivity
• in the late 1800s, Henri Becquerel and Marie Curie
discovered that certain elements would constantly
emit small, energetic particles and rays
• these energetic particles could penetrate matter
• Ernest Rutherford discovered that there were three
different kinds of emissions
 alpha, a, particles with a mass 4x H atom and + charge
 beta, b, particles with a mass ~1/2000th H atom and –
charge
 gamma, g, rays that are energy rays, not particles
19
Radioactivity
• Three types of radiation were discovered by
Ernest Rutherford:
  particles
  particles
  rays
20
Discovery of the Nucleus
• Ernest Rutherford
(c.a. 1908) utilized
radioactivity in the gold
foil experiment to prove
that the plum-pudding
model of the atom was
wrong.
• In so doing, he
discovered the atomic
nucleus and the proton.
Ernest Rutherford
21
The Gold-Foil Experiment
22
Rutherford’s Results
• Over 98% of the  particles went straight
through
• About 2% of the  particles went through
but were deflected by large angles
• About 0.01% of the  particles bounced
off the gold foil
“...as if you fired a 15” cannon shell at a piece
of tissue paper and it came back and hit you.”
23
Rutherford’s Conclusions
• Atoms were mostly empty space
because almost all the particles went straight
through
• Atoms contain a dense particle that was small in
volume compared to the atom but large in mass
because of the few particles that bounced back
• This dense particle was positively charged
because of the large deflections of some of the
particles
24
Plum Pudding
Atom
•
•
•
•
•
•
•
•
•
•
a few of the
 particles
do not go through
•
•
•
•
•
•
•
•
•
•
•
•
if atom was like
a plum pudding,
all the  particles
should go
straight through
Nuclear Atom
.
.
.
most  particles
go straight through
some  particles
go through, but are deflected
25
Rutherford’s Interpretation –
the Nuclear Model
1) The atom contains a tiny dense center called the
nucleus
 the amount of space taken by the nucleus is only about
1/10 trillionth the volume of the atom
2) The nucleus has essentially the entire mass of the
atom
 the electrons weigh so little they give practically no mass
to the atom
3) The nucleus is positively charged
 the amount of positive charge balances the negative
charge of the electrons
4) The electrons are dispersed in the empty space of
the atom surrounding the nucleus (electron cloud)
26
Structure of the Atom
• Rutherford proposed that the nucleus
had a particle that had the same amount
of charge as an electron but opposite
sign
 based on measurements of the nuclear
charge of the elements
• these particles are called protons
 charge = +1.60 x 1019 C
 mass = 1.67262 x 10-24 g
• since protons and electrons have the
same amount of charge, for the atom to
be neutral there must be equal numbers
of protons and electrons
27
The Nuclear Atomic Model
28
Rutherford’s Model of
the Atom
atomic radius ~ 100 pm = 1 x 10-10 m
nuclear radius ~ 5 x 10-3 pm = 5 x 10-15 m
“If the atom is the Cowboys Stadium, then the
nucleus is a marble on the 50-yard line.”
29
2.2
Atomic Theory from 1800-1911
30
Some Problems
• How could beryllium have 4 protons stuck
together in the nucleus?
shouldn’t they repel each other?
• If a beryllium atom has 4 protons, then it
should weigh 4 amu; but it actually weighs
9.01 amu! Where is the extra mass coming
from?
each proton weighs 1 amu
remember, the electron’s mass is only about
0.00055 amu and Be has only 4 electrons – it
can’t account for the extra 5 amu of mass
31
There Must Be Something Else There!
• to answer these questions, Rutherford
proposed that there was another particle in
the nucleus – it is called a neutron
• neutrons have no charge and a mass of 1
amu
mass = 1.67493 x 10-24 g
slightly heavier than a proton
no charge
32
The Sub-Atomic Particles
Subatomic
Mass
Mass
Location Charge Symbol
Particle
g
amu
in atom
Proton
1.67262 1.00727
nucleus
+1
p, p+, H+
empty
-1
e, e-
0
n, n0
x 10-24
Electron
0.00091 0.00055
x 10-24
Neutron
1.67493 1.00866
space
nucleus
x 10-24
33
Elements
• each element has a unique number of
protons in its nucleus
the number of protons define the element
• the number of protons in the nucleus of an
atom is called the atomic number
the elements are arranged on the Periodic
Table in order of their atomic numbers
• Each element also has a corresponding
mass number.
Protons + neutrons.
34
35
Elements
• Each element has a unique name and symbol.
 The symbol is either one or two letters
 One capital letter or one capital letter + one lower case letter.
H = Hydrogen = “water-former”
Br = Bromine = ‘stench’
Liquid Bromine
36
The Periodic Table of Elements
Atomic number
Element symbol
Atomic
mass
37
Elemental & Isotope Notation
Atomic number (Z) = number of protons in nucleus
Mass number (A) = number of protons + number of neutrons
= atomic number (Z) + number of neutrons
Mass Number
Atomic Number
A
ZX
238
92
Element Symbol
U
Isotope Notation = Uranium-238
2.3
Example: How many protons, electrons,
and neutrons are in an atom of 52
24 Cr ?
Given:
Find:
Concept Plan:
52
24 Cr
therefore A = 52, Z = 24
# p+, # e-, # n0
symbol
symbol
Relationships:
Solution:
Check:
atomic
number
atomic & mass
numbers
# p+
# e-
# n0
in neutral atom, # p+ = # emass number = # p+ + # n0
Z = 24 = # p+
# e- = # p+ = 24
A = Z + # n0
52 = 24 + # n0
28 = # n0
for most stable isotopes, n0 > p+
39
Isotopes:
• Isotopes = atoms of the same element with different
masses.
• Isotopes have different numbers of neutrons.
11
C
6
12
C
6
13
C
6
14
C
6
Carbon-11
Carbon-12
Carbon-13
Carbon-14
40
Neon
Number of
protons
Symbol
Number of
neutrons
A, mass
number
Percent
natural
abundance
Ne-20 or
20 Ne
10
10
10
20
90.48%
Ne-21 or
21 Ne
10
10
11
21
0.27%
Ne-22 or
22 Ne
10
10
12
22
9.25%
41
Mass Spectrometer
42
Tro: Chemistry: A Molecular Approach, 2/e
Mass Spectrum
• A mass spectrum is a
graph that gives the
relative mass and relative
abundance of each
particle
• Relative mass of the
particle is plotted in the
x-axis
• Relative abundance of
the particle is plotted in
the y-axis
43
Atomic Mass
Atomic mass is the mass of an atom in atomic
mass units (amu)
By definition:
1 atom 12C “weighs” 12 amu
1 amu = 1.6606 x 10-24 g
On this scale
1H
= 1.008 amu
16O
= 16.00 amu
3.1
Average Atomic Mass
• Because in the real world we use large
amounts of atoms and molecules, we use
average masses in calculations.
• Average atomic mass is calculated from
the isotopes of an element weighted by
their relative abundances.
45
Natural lithium is:
6Li
(6.015 amu) = 7.42%
7Li
(7.016 amu) = 92.58%
Average atomic mass of lithium:
(7.42 x 6.015) + (92.58 x 7.016) / 100 = 6.941 amu
46
Charged Atoms
• The number of protons determines the
element.
All sodium atoms have 11 protons in the nucleus.
• In a chemical change (aka: a reaction), the
number of protons in the nucleus of the atom
doesn’t change, however the number of
electrons may.
• Atoms in a compound that gain or lose
electrons and have a charge, these are called
ions.
47
Types of Ions
Cation – ion with a positive charge
If a neutral atom loses one or more electrons
it becomes a cation.
Na
11 protons
11 electrons
Na+
11 protons
10 electrons
Cl-
17 protons
18 electrons
Anion – ion with a negative charge
If a neutral atom gains one or more electrons
it becomes an anion.
Cl
17 protons
17 electrons
2.5
Ions of Hydrogen
49
Ions
A monatomic ion contains only one atom
Na+, Cl-, Ca2+, O2-, Al3+, N3-
A polyatomic ion contains more than one atom
OH-, CN-, NH4+, NO3-
Nitrate
Polyatomic
Ion
50
Practice—Fill in the Table.
Ion
p+
e-
-
Cl
K+
2-
S
Sr
2+
51
Practice—Fill in the Table,
Continued.
+
-
p
e
1-
17
18
1+
19
18
S2-
16
18
38
36
Ion
Cl
K
Sr
2+
52
Example —Find the Number of Protons
and Electrons in Ca2+.
Review
• What is the atomic number of boron, B?
• What is the atomic mass of silicon, Si?
• How many protons does a chlorine atom have?
• How many electrons does a neutral neon atom have?
• Will an atom with 6 protons, 6 neutrons and 6
electrons be electrically neutral?
• Will an atom with 27 protons, 32 neutrons, and 27
electrons be electrically neutral?
• Will an Na atom with 10 electrons be electrically
neutral?
54