Download Unit 2 Atomic structure

Unit 1: Atoms
Level 3 Achievement Scale
 Can state the key results of the experiments associated with Dalton,
Rutherford, Thomson, Chadwick, and Bohr and what this lead each to
conclude.
 Can explain that the electrons are not massless but that in comparison to
nucleus are insignificant to mass of the atom.
 Can explain the role of the 3 fundamental forces (strong nuclear, weak nuclear
and electromagnetic) in the atom.
 Can determine the number of each of the subatomic particle in an atom when
specifically given the atomic number, atomic mass, mass number, atomic mass
unit and/or charge.
 Can state the energy levels in which electrons exist when given an atom or ion
and its charge.
 Can explain that energy must be absorbed to change an atom from the ground
sate to the excited state and that this transfer (absorption or emission)
happens when electrons transfer between energy levels.
 Can draw atomic models of atoms, ions and isotopes when given specific
information (atomic number and mass, charge).
Atoms broken down further
• Nucleus – Center of atom: Dense
– Protons and Neutrons: similar in size and mass
• Protons – positive charge
• Neutrons – no electric charge
• Outside the Nucleus
– Electrons – cloud of tiny particles with little mass
• Electrons – negative charge (-1)
• Size – If the atom was the size of Brown’s
stadium the nucleus would be the size of a
small marble on the 50 yard line.
The Nucleus and Structure of the Atom
• Atoms are made of three kinds of
particles: electrons, protons, and neutrons.
The mass of the electron is REAL small compared to protons and neutrons.
Number VS Mass
• Atomic Number
– # of protons in an
atom
• Atomic Mass
– # of protons and neutrons
Element = # protons
Atomic number
= # protons
Every Element had
a certain atomic #
Isotope = relates to # neutrons
• All 3 are lithium because all 3 have same #
of protons.
• Isotope: vary in mass because the # of
neutrons differ.
ISOTOPES
•Result when neutrons are
added to an atom
•Vary in mass but are the same
element because proton # is
not changed
2
H
1
H
1
3
1
H
Mass Number
Nuclear Notation
(# protons + # neutrons)
12
Atomic Number
(# protons)
6
Mass # --- Atomic # = neutron #
12 – 6 = 6 neutrons
Neutral Atoms
• Uncharged atom
–Results because
+ protons = - electrons
If you change the _____ ….
• If you change the PROTON,
you change the _________
ELEMENT
• If you change the NEUTRON,
ISOTOPE
you change the _________
• If you change the ELECTRON,
ION
you change the _________
How many
protons?
How many
electrons?
How many
neutrons?
6
6
8
Draw a atomic
model for this
element?
14
6
2 4
How many
protons?
3
How many
electrons? 3
How many
neutrons?
4
Draw a atomic
model for this
element?
7
3
2 1
How many
protons?
7
How many
electrons?
7
How many
neutrons?
7
Draw a atomic
model for this
element?
14
2 5
Ions
• Ion: An atom that has a
charge
• Results from a loss or
gain of an electron
• 1+ = loss of an electron
• 1- = gain of an electron
25
12
Mg
+
2
Protons = 12
Neutron = 13
Electrons = 10
Atomic Mass Unit
• AMU
– Is equal to 1/12th of the mass of a carbon
atom
– 1 AMU = isotope of carbon ( 6 protons / 6
neutrons)
• Average atomic mass – weighted avg.
The structure of the atom
• Electrons are bound to
the nucleus by
electromagnetic forces.
• The force is the
attraction between
protons (positive) and
electrons (negative).
 The momentum of the electron causes it to move
around the nucleus rather than falling straight in.
The structure of the atom
• The strong nuclear force attracts
neutrons and protons to each other,
otherwise the positively charged protons
would repel each other.
The structure of the atom
• The weak force is weaker than both the electric force and
the strong nuclear force.
• If you leave a solitary neutron outside the nucleus, the
weak force eventually causes it to break up into a proton
and an electron.
• The force of gravity inside the atom is much weaker even
than the weak force.
 Every process we
know in the universe
can be explained in
terms of these
fundamental forces.
Forces
• Electromagnetic
• Force that keeps the
electrons from
crashing into the
nucleus – created by
momentum
• Strong Nuclear
• Force that keeps the
nucleus together –
protons repel each
other.
• Strongest force
known to science
How do atoms function? Atoms are Picky!
When a photon with
exactly the right energy
comes along, an electron
will be kicked into a
higher orbit
The photon is absorbed,
and the electron jumps to
higher (excited) state.
Electronic Energy States
• Electrons can only
have certain
energies; other
energies are not
allowed.
• Each type of atom
has a unique set of
energies.
Bohr model of the atom
• Danish physicist Neils Bohr
proposed the concept of energy
levels to explain the spectrum of
hydrogen.
• When an electron moves from a
higher energy level to a lower
one, the atom gives up the energy
difference between the two levels.
• The energy comes out as different
colors of light.
Electrons in the atom
• Each different element has
its own characteristic
pattern of colors called a
spectrum.
• The colors of clothes, paint,
and everything else around
you come from this property
of elements to emit or
absorb light of only certain
colors.
Electrons in atoms
• Each individual color in a spectrum is called a
spectral line because each color appears as a
line in a spectroscope.
• A spectroscope is a device that spreads light
into its different colors.
Electrons and energy levels
• In the current model of the atom, we think of the
electrons as moving around the nucleus in an
area called an electron cloud.
• The energy levels occur because electrons in
the cloud are at different average distances from
the nucleus.
Rules for energy levels
Inside an atom, electrons always obey these rules:
1. The energy of an electron must match one of the
energy levels in the atom.
2. Each energy level can hold only a certain
number of electrons, and no more.
2
8
8
18
3. As electrons are added to an atom, they settle into
the lowest unfilled energy level.
Energy levels
• In the Bohr model of
the atom, the first
energy level can
accept up to two
electrons.
• The second and
third energy levels
hold up to eight
electrons each.
• The fourth and fifth
energy levels hold
18 electrons.
• Heat added puts
electrons at a higher
energy level –
coming down emits
light.
• Different elements
burn different colors
because light is
emitted a different
wave frequencies
Fireworks
14.2 The quantum theory
• Quantum theory says that when things get
very small, like the size of an atom, matter
and energy do not obey Newton’s laws or
other laws of classical physics.
14.2 The quantum theory
• According to quantum
theory, particles the size
of electrons are
fundamentally different
• An electron appears in a
wave-like “cloud and has
no definite position.
14.2 The quantum theory
• The work of German physicist Werner
Heisenberg (1901–1976) led to Heisenberg’s
uncertainty principle.
• The uncertainty principle explains why a particle’s
position, momentum or energy can never be
precisely determined.
• The uncertainty principle exists because
measuring any variable disturbs the others in an
unpredictable way.
14.2 The uncertainty principle