Download 4.1 Studying Atoms

Chapter 4 – Atomic Structure
4.1 Studying Atoms
Democritus (460-371 B.C.)
Democritus believed matter consisted of small, indivisible
particles (called atoms)
Believed…
solid atoms – rough and prickly
liquid atoms – round and smooth
4.1 Studying Atoms
Aristotle (384-322 B.C.)
Aristotle believed matter consisted of four elements
Believed that there is no limit to how many times matter
can be divided
4.1 Studying Atoms
John Dalton (1766-1844)
Found that the ratio of Magnesium to Oxygen in the above
reaction is always 2:1.
4.1 Studying Atoms
Dalton’s Atomic Theory
1. All elements composed
of atoms
2. Atoms of same element
have same mass
Wooden spheres used by Dalton to model atoms
3. Compounds contain atoms of more than one element
4. In a compound, atoms of different elements combine in
the same way
4.1 Studying Atoms
Dalton’s Model of the Atom
solid sphere
4.1 Studying Atoms
J J Thomson (1856-1940)
Used a cathode ray tube to study the atom
4.1 Studying Atoms
Cathode ray tube
4.1 Studying Atoms
Cathode ray tube
4.1 Studying Atoms
-beam deflected towards
positive charge, away from
negative charge
(negatively charge)
-beam turns a small
paddle wheel
(has mass)
4.1 Studying Atoms
most air
removed
The beam has mass. Where did it come from???
The matter making up this beam must come from the
matter making up the metal plates, but its mass was
1/2000th the mass of the lightest known atom (Hydrogen)
The atoms making the plates must be made of smaller,
negatively charged particles!!!!!!
4.1 Studying Atoms
But, an atom is neutral.
How can it contain
negative particles??
There must be positive
charge in the atom also!!
4.1 Studying Atoms
J J Thomson’s Model of the Atom
Dalton model
plum pudding model
4.1 Studying Atoms
4.1 Studying Atoms
Ernest Rutherford (1871–1937)
Discovered that Uranium emits alpha particles
4.1 Studying Atoms
Rutherford Gold Foil Experiment
4.1 Studying Atoms
Wanted to know what happens to alpha particles
when they pass through a sheet of gold foil?
Predicted alpha particles would pass right by the atoms
in thin, gold foil
4.1 Studying Atoms
Rutherford Gold Foil Experiment
4.1 Studying Atoms
Many particles were deflected, some more than 90 degrees
“It was almost as incredible as if you fired a 15-inch artillery
shell at a piece of tissue paper and it came back and hit you”
4.1 Studying Atoms
Rutherford’s Model of the Atom
Dalton model
plum pudding
model
planetary model
4.1 Studying Atoms
nucleus – dense, positively charged
mass located in the center of the atom.
The volume of the
atom is a trillion
times the volume of
its nucleus
Houston Astrodome
4.2 The Structure of the Atom
Rutherford saw evidence for the existence of two subatomic
particles, and predicted the existence of a third.
Particle Type
Location
Charge
Symbol
proton
nucleus
+1
p+
electron
outside the nucleus
-1
e-
neutron
nucleus
0
n
Protons and neutrons have the same mass, but electrons
are much less massive
4.2 The Structure of the Atom
4.2 The Structure of the Atom
With the discovery of subatomic particles, scientists were
able to describe the difference between types of atoms
Atoms of different elements have different numbers of protons
1
H
atomic number – equals
the number of protons
also equals the number
of electrons
Hydrogen
1.0079
atomic mass
4.2 The Structure of the Atom
mass number – the sum of the protons and neutrons in an
atom
number of neutrons
number of neutrons
=
mass number – atomic number
quite often, the atomic mass rounded to a whole number is
equal to the mass number
4.2 The Structure of the Atom
How many protons does Oxygen have?
How many electrons does Oxygen have?
4.2 The Structure of the Atom
What is the atomic number of oxygen?
What is the mass number of oxygen?
4.2 The Structure of the Atom
isotopes – atoms of the same element that have different
numbers of neutrons
There are three isotopes of oxygen:
8
oxygen-16
O
Oxygen
oxygen-17
oxygen-18
mass
number
15.999
How many neutrons in oxygen-17?
4.2 The Structure of the Atom
17
Cl
Chlorine
35.453
How many protons, electrons,
and neutrons are there in an
atom of chlorine-37?
4.2 The Structure of the Atom
6
C
Carbon
12.011
How many protons, electrons,
and neutrons are there in an
atom of carbon-12?
How many protons, electrons,
and neutrons are there in an
atom of carbon-14?
4.3 Modern Atomic Theory
What can happen when an atom absorbs energy?
- an increase in kinetic energy or a phase change
energy may be
absorbed by an
atom, then emitted
as light
4.3 Modern Atomic Theory
Niels Bohr (1885-1962)
agreed with Rutherford’s model but
added something to it
energy levels – the possible energies that electrons in an
atom can have
4.3 Modern Atomic Theory
when an atom gains energy an electron may move to a
higher energy level
when it loses the energy
it emits it as light
no two elements have the same set of energy levels, so the
emit different colors of light
4.3 Modern Atomic Theory
Electron Cloud Model
electron cloud model – model of the most likely locations for
electrons in an atom (deals with probability)
4.3 Modern Atomic Theory
Electron Cloud Model of a Hydrogen Atom
4.3 Modern Atomic Theory
4.3 Modern Atomic Theory
orbital – region of space where an electron is likely to be found
4.3 Modern Atomic Theory
electron cloud – a good approximation of how electrons
behave in their orbitals
Energy Level, Orbitals, and Electrons
Energy Level
Number of
Orbitals
Maximum # of
Electrons
1
1
2
2
4
8
3
9
18
4
16
32
4.3 Modern Atomic Theory
electron configuration – arrangement of electrons in the
orbital of an atom
ground state – electrons are all in their lowest possible
energy levels (most stable)
excited state – one or more electrons are in a higher energy
level than usual (least stable)
atoms emit light when their
electrons return to ground
state
Chapter 4 Vocabulary
isotopes
proton
nucleus
mass number
electron configuration
energy levels
atomic number
neutron
orbital
electron cloud
electron
excited state
ground state
Chapter 4 Vocabulary
isotopes
proton
nucleus
mass number
energy levels
atomic number
neutron
orbital
electron cloud
electron
excited state
ground state
Chapter 4 Vocabulary
isotopes
proton
mass number
energy levels
atomic number
neutron
orbital
electron cloud
electron
excited state
ground state
Chapter 4 Vocabulary
isotopes
proton
mass number
energy levels
atomic number
orbital
electron cloud
electron
excited state
ground state
Chapter 4 Vocabulary
isotopes
proton
mass number
energy levels
atomic number
electron cloud
electron
excited state
ground state
Chapter 4 Vocabulary
isotopes
proton
mass number
energy levels
atomic number
electron cloud
electron
ground state
Chapter 4 Vocabulary
isotopes
proton
mass number
energy levels
electron cloud
electron
ground state
Chapter 4 Vocabulary
proton
mass number
energy levels
electron cloud
electron
ground state
Chapter 4 Vocabulary
proton
mass number
electron cloud
electron
ground state
Chapter 4 Vocabulary
proton
electron cloud
electron
ground state
Chapter 4 Vocabulary
proton
electron
ground state
Chapter 4 Vocabulary
proton
electron
Chapter 4 Vocabulary
proton
Chapter 4 Vocabulary