Transcript PowerPoint - Models of the Atom

The Atom and You
(What are we made of?)
Page 3
Early Greek Theories
• 400 B.C.
• Democritus thought matter could not
be divided indefinitely.
• Called the smallest particle ‘Atomos’
Democritus
• Atom - Smallest particle of an element that
retains the chemical identity of that element
Comparison
•World population:
7,000,000,000
•Atoms in Cu penny:
29,000,000,000,000,000,000,000
John Dalton
• 1800 -Dalton proposed a modern atomic model
based on experimentation not on pure reason.
• All matter is made of atoms.
• Atoms of an element are identical.
• Atoms of different elements combine
in constant ratios to form compounds.
• Atoms are rearranged in reactions.
• His ideas account for the law of conservation of
mass (atoms are neither created nor destroyed)
and the law of constant composition (elements
combine in fixed ratios).
J.J. Thomson (1897)
• Applied electric and magnetic fields to
cathode rays and got particles that shot off.
• These particle were negative, electrons.
• “Plum pudding” model of the atom
Negative particles in a
positive matrix.
V.Montgomery & R.Smith
6
Ernest Rutherford
• Rutherford shot alpha () particles at gold foil.
Zinc sulfide screen
Thin gold foil
Lead block
Radioactive
substance path of invisible
-particles
Most particles passed through.
So, atoms are mostly empty.
Some positive -particles
deflected or bounced back!
Thus, a “nucleus” is positive &
holds most of an atom’s mass.
Bohr’s model
•Electrons orbit the nucleus in “shells”
•Proposed that electrons must have enough
energy to keep them in constant motion
around the nucleus
•Analogous to the motion of the planets
orbiting the sun
•The further away,
the more energy the
electron has
Modern Model – Wave Mechanical
Model (Electron Cloud)
• Based on the work of many scientists
• Protons (+) and neutrons (0) are in the
nucleus
• Electrons (-) are in an orbital (not an exact
location of the electron, it is a probable
place that the electron is located.
• The thickest (most dense) part of the cloud
is the most probable place of the electron orbital
Wave Mechanical Model
(Electron Cloud)
electron
neutron
proton
Regents Question:
Subatomic particles can usually pass undeflected
through an atom because the volume of an atom
is composed of
(1) an uncharged nucleus
(2) largely empty space
(3) neutrons
(4) protons
Regents Question:
One model of the atom states that atoms are tiny
particles composed of a uniform mixture of positive
and negative charges. Scientists conducted an
experiment where alpha particles were aimed at a
thin layer of gold atoms.
Most of the alpha particles passed directly through
the gold atoms. A few alpha particles were deflected
from their straight-line paths. An illustration of the
experiment is shown below.
•Most of the alpha particles passed directly
through the gold atoms undisturbed. What
does this evidence suggest about the structure
of the gold atoms? Most of the atom is empty space.
•A few of the alpha particles were deflected.
What does this evidence suggest about the
structure of the gold atoms?
There is central + charge. The nucleus is +.
•How should the original model be revised
based on the results of this experiment?
The atom is not a uniform mixture of + and - charge.
Positive charge is located in a heavy central mass.
In the wave-mechanical
model (electron cloud model),
the electrons are in orbitals,
which are defined as the
regions of the most probable
electron location (ground
state).
An orbital is the area of highest
probability of finding an electron.
Notes Now
• Take out paper.
• Atoms are made of smaller particles.
– Protons
– Neutrons
– Electrons
Subatomic Particles
Symbol Location Charge
electron
proton
neutron
Mass
Subatomic Particles
Symbol Location Charge
electron
e−
proton
p+
neutron
n
Mass
Subatomic Particles
Symbol Location Charge
−
empty
space
electron
e
proton
p+
nucleus
neutron
n
nucleus
Mass
Subatomic Particles
Symbol Location Charge
−
empty
space
−1
electron
e
proton
p+
nucleus
+1
neutron
n
nucleus
0
Mass
Subatomic Particles
Symbol Location Charge
Mass
empty
space
−1
0.0005
amu
−
electron
e
proton
p+
nucleus
+1
1 amu
neutron
n
nucleus
0
1 amu
Regents Question:
Which statement best describes electrons?
(1) They are positive subatomic particles and are found in
the nucleus.
(2) They are positive subatomic particles and are found
surrounding the nucleus.
(3) They are negative subatomic particles and are found in
the nucleus.
(4) They are negative subatomic particles and are found
surrounding the nucleus.
Regents Question:
In the modern model of the atom, each atom is composed of
three major subatomic (or fundamental) particles.
•
Name the subatomic particles contained in the nucleus of
the atom.
Proton and neutron
•
State the charge associated with each type of subatomic
particle contained in the nucleus of the atom.
Proton is positive and the neutron is neutral
•
What is the net charge of the nucleus?
Positive
Regents Question:
Which subatomic particle has no charge?
(1) alpha particle
(2) beta particle
(3) Neutron
(4) electron
Electron Configurations
• Electron Configurations: arrangement of ein an atom.
• There is a distinct electron configuration for
each atom in the ground state.
• It is listed on the Periodic Table.
•The outermost electrons in an atom are
called the valence electrons.
•In general, the number of valence electrons
affects the chemical properties of an
element.
The ground state for Na is 2-8-1
•The valence shell is the third shell.
•The valence shell contains 1 electron.
Regents Question
What is the total number of electrons in the
valence shell of an atom of aluminum in the
ground state?
(1) 8
(2) 2
(3) 3
(4) 10
Regents Question: 06/02 #31
In which shell are the valence electrons of the elements
in Period 2 found?
(1) 1
(2) 2
(3) 3
(4) 4
Page 4
1. Find element on the Periodic Table.
2. Use the bolded number for number of
electron. This is the Atomic Number.
3. The first shell can only contain 2 electron.
4. The next shells have electrons according to
the formula 2n2.
5. Draw the correct number of shells and
electrons
Sodium - Na
1. Na is element number 11.
2. The bold number is 11, so the electrons
equal 11.
3. First shell has 2.
4. The second has 8, so we need three shells.
5. Draw three circles an add the correct
number of electrons.
Complete page 4, numbers 2-5.
Page 5
Notes Now
• Take out paper.
Ions
• When an atom, (neutral), gain or loses and
electron it is known as an ION.
• I do not drink GIN.
• It makes my LIPs burn.
•Ion
•atom with an electrical charge
•Anion
•more electrons than protons: - charge
•Cation
•more protons than electrons: + charge
How many electrons, protons and neutrons?
25
2+
Mg
12
Anion or Cation?
How many electrons, protons and neutrons?
179
Hf
72
Anion or Cation?
4+
How many electrons, protons and neutrons?
37
−
Cl
17
Anion or Cation?
Page 4
Sodium Ion –
+1
Na
1. Na is element number 11.
2. The bold number is 11, so the electrons equal
11. Take into account the charge.
3. +1 means one less electron. LIP – losing is
positive. First shell has 2.
4. First shell has 2. The second has 8. There is no
third shell.
5. Draw two circles an add the correct number of
electrons.
Complete page 4, numbers 7-10.
Page 8
Review Time
• Take out paper.
Atomic Particles
• Atomic Number
– Number of protons
– Number of positive charges
– Number of electrons in a neutral atom
• Mass Number
– The mass of an atom (amu)
How many electrons, protons and neutrons?
14
N
7
How many electrons, protons and neutrons?
15
N
7
Isotopes
• Atoms of the same element with the same
atomic number but different mass number
• Ex. Protium - Hydrogen proton =1
neutron = 0
Deuterium – Hydrogen proton = 1
neutron = 1
Tritium – Hydrogen proton = 1
neutron = 2
Mass number
The number of protons plus
neutrons in an atom
Commonly follows chemical
symbol:
Ni-59
How many electrons, protons and neutrons?
Iron-56 OR
Fe-56
What has 5 protons and 6 neutrons?
Page 11
Regents Question:
The number of neutrons in the nucleus of an atom can be
determined by
(1) Adding the atomic number to the mass number
(2) Subtracting the atomic number from the mass number
(3) Adding the mass number to the atomic mass
(4) Subtracting the mass number from the atomic number
Regents Question:
The atomic number of an atom is always equal to the
number of its
(1) protons, only
(2) neutrons, only
(3) protons plus neutrons
(4) protons plus electrons
Regents Question:
What is the total number of protons in the
nucleus of an atom of potassium-42?
(1) 15
(2) 19
(3) 39
(4) 42
The mass number (42) is not
necessary to find the number of
protons.
Regents Question:
The nucleus of an atom of K-42 contains
(1) 19 protons and 23 neutrons
(2) 19 protons and 42 neutrons
(3) 20 protons and 19 neutrons
(4) 23 protons and 19 neutrons
Regents Question:
An atom of carbon-12 and an atom of carbon-14 differ in
(1) Atomic number
(2) Atomic mass
(3) Nuclear charge
(4) Number of electrons
Carbon-12 and carbon-14 are isotopes.
Regents Question:
All the isotopes of a given atom have
(1) the same mass number and same atomic number
(2) the same mass number but different atomic numbers
(3) different mass numbers but the same atomic number
(4) different mass numbers and different atomic number
Regents Question:
Atoms of the same element that have different numbers
of neutrons are classified as
(1) Charged atoms
(2) Charged nuclei
(3) Isomers
(4) Isotopes
Take Out Periodic Table
• What is the mass of the following:
H C Cl
Periodic Table
Shows Atomic Mass
•Atomic Mass
•average mass of an element’s atoms
averaged according to their relative
abundance
•sum of relative abundances x isotope mass
WHAT?
Why is:
Atomic mass = 35.453 for Cl?
(Shouldn’t it be a whole number?)
All elements have Isotopes
Remember Isotopes Are
•
•
•
•
•
Same element
Different number of neutrons
Different Mass Numbers
Isotopes occur in different amounts
Remember Carbon Dating from Earth
Science?
How do we calculate Atomic Mass?
(AKA Average Atomic Mass)
1. Use the Mass number of the Isotopes.
2. Multiply that number by the percentage.
3. Add the resulting number together.
37 * .25 = 9.25
35 * .75 = 26.25
35.5
The average atomic mass of an
element is the weighted average
of the masses of its naturally
occurring isotopes.
Isotope Mass Abundance
Calculation
12C
12
98.89%
12 x .9889 =
13C
13
1.108%
13 x 0.01108 = 0.1440
Atomic Mass (weighted average)
11.87
12.01 amu
Regents Question:
The atomic mass of an element is calculated using
the
(1) atomic number and the ratios of its naturally
occurring isotopes
(2) atomic number and the half-lives of each of its
isotopes
(3) masses and the ratios of its naturally occurring
isotopes
(4) masses and the half-lives of each of its isotopes
Regents Question:
Hydrogen has three isotopes with mass numbers of 1, 2,
and 3 and has an average atomic mass of 1.00794
amu. This information indicates that
(1) Equal number of each isotope are present
(2) More isotopes have an atomic mass of 2 or 3 than 1
(3) More isotopes have an atomic mass of 1 rather than 2
of 3
(4) Isotopes have only an atomic mass of 1
Regents Question:
In which list are the elements arranged in order of
increasing atomic mass?
(1) Cl, K, Ar
(2) Fe, Co, Ni
(3) Te, I Xe
(4) Ne, F, Na
Look for the masses on the periodic
table of the elements.
Page 12
Notes Again
• Take out paper
The Excited State
• When an electron in an atom gains a
specific amount of energy, the electron
is at a higher energy state (excited
state).
How is Sodium excited?
•Change the electron configuration
•Normal electron configuration is
•2-8-1
•Possible excited states for Na are:
• 2-7-2
•1-8-2
What are possible excited states
for the following:
•
•
•
•
•
•
•
Hydrogen
Gold
Potassium
Chlorine
Magnesium
Manganese
Flourine
When an electron returns from a
higher energy state to a lower
energy state, a specific amount
of energy is emitted. This emitted
energy can be used to identify an
element.
Emission Spectrum
Regents Question:
During a flame test, ions of a specific metal are heated in
the flam of a gas burner. A characteristic color of light
was emitted by these ions in the flame when the
electrons
(1) Gain energy as they return to lower energy levels
(2) Gain energy as they move to higher energy levels
(3) Emit energy as they return to lower energy levels
(4) Emit energy as they move to higher energy levels
Regents Question:
When the electrons of an excited atom return to a
lower energy state, the energy emitted can result
in the production of
(1) alpha particles
(2) Isotopes
(3) protons
(4) spectra
Regents Question:
Base your answers to the next two questions on the
electron configuration table shown below.
•
What is the total number of valence electrons in an
atom of electron configuration X?
2
•
Which electron configuration represents the excited
state of a calcium atom?
2-8-7-3
Element
X
Y
Z
Electron
Configuration
2 –8 –8 –2
2 –8 –7 –3
2 –8 –8