Atomic structure

1
Atomic Theory
2
Theories Change

• The Atomic Theory of Matter states that all
  matter is composed of small, fast moving
  particles called atoms. These atoms can join
  together to form molecules.
• This theory is really thousands of individual
  theories that provide evidence for the whole
  theory.

3
HISTORY OF THE ATOM
Democritus develops the idea of atoms
460 BC
He pounded up materials in his pestle and mortar
until he had reduced them to smaller and smaller
particles which he called
ATOMA (greek for indivisible)
4
HISTORY OF THE ATOM
John Dalton
1808
Suggested that all matter was made up of tiny
spheres that were able to bounce around with
perfect elasticity and called them
ATOMS
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Daltons Atomic Theory (1808)

1. Elements are composed of extremely small
   particles called atoms. All atoms of a given
   element are identical. The atoms of one element
   are different from the atoms of all other
   elements.

1. Compounds are composed of atoms of more than one
   element.

1. Chemical reactions only involve the rearrangement
   of atoms. Atoms are not created or destroyed in
   chemical reactions.

2.1
6
8 X2Y
Law of Conservation of Mass
2.1
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HISTORY OF THE ATOM
Joseph John Thompson
1898
Found that atoms could sometimes eject a far
smaller negative particle which he called an
ELECTRON
8
HISTORY OF THE ATOM
1904
Thompson develops the idea that an atom was made
up of electrons scattered unevenly within an
elastic sphere surrounded by a soup of positive
charge to balance the electron's charge
like raisins in a muffin.
Raisins in a Muffin MODEL
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2.2
10
HISTORY OF THE ATOM
Ernest Rutherford
1910
He fired Helium nuclei at a piece of gold foil
which was only a few atoms thick. He found that
although most of them passed through. About 1 in
10,000 hit
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HISTORY OF THE ATOM
gold foil
helium nuclei
helium nuclei
They found that while most of the helium nuclei
passed through the foil, a small number were
deflected and, to their surprise, some helium
nuclei bounced straight back.
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(1908 Nobel Prize in Chemistry)

1. atoms positive charge is concentrated in the
   nucleus
2. proton (p) has opposite () charge of electron
3. mass of p is 1840 x mass of e- (1.67 x 10-24 g)

2.2
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Rutherfords 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 Houston Astrodome Then the
nucleus is a marble on the 50 yard line
2.2
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HISTORY OF THE ATOM
Rutherfords new evidence allowed him to propose
a more detailed model with a central nucleus.
He suggested that the positive charge was all
in a central nucleus. With this holding the
electrons in place by electrical
attraction However, this was not the end of the
story.
15
HISTORY OF THE ATOM
Niels Bohr
1913
Studied under Rutherford at the Victoria
University in Manchester.
Bohr refined Rutherford's idea by adding that the
electrons were in orbits. Rather like planets
orbiting the sun. With each orbit only able to
contain a set number of electrons.
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Bohrs Atom
electrons in orbits
nucleus
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HELIUM ATOM
Shell
proton
N

-

N
-
neutron
electron
What do these particles consist of?
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All atoms are made up of just 3 basic sub-atomic
particles-
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ATOMIC STRUCTURE
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Notes Atomic Theory

1. All atoms of a given element are identical. The
   atoms of one element are different from the atoms
   of all other elements.
2. Atoms are not created or destroyed in chemical
   reactions, they are only rearrange.
3. Compounds are composed of atoms of more than one
   element.
4. Subatomic particles are protons, neutrons and
   electrons.
5. Protons and neutrons are together in the nucleus

21
Notes Atomic Theory

1. Electrons are in motion in orbits around the
   central nucleus.
2. Protons carry a positive electrical charge,
   electrons carry a negative charge, and neutrons
   carry no charge.
3. Neutrons work to keep nuclei together.
4. Most atoms are electrically neutral, meaning that
   they have an equal number of protons and
   electrons.

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Notes ATOMIC STRUCTURE
Symbol
He
2
Atomic number
the number of protons in an atom
4
Atomic mass
Helium
the number of protons and neutrons in an atom
Name
Number of electrons Number of protons
Isotopes are atoms with the same number of
protons and different number of neutrons.
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Isotopes are atoms of the same element (X) with
different numbers of neutrons in the nucleus
2.3
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2.3
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Do You Understand Isotopes?
6 protons, 8 (14 - 6) neutrons, 6 electrons
6 protons, 5 (11 - 6) neutrons, 6 electrons
2.3
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Lets practice!!!

• Complete The Atoms Family - Atomic Math
  Challenge.
• Play with gizmo www.explorelearning.com

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Structure of the Atom

• The Atomic Number of an atom number of
  protons in the nucleus.
• The Atomic Mass of an atom number of
  Protons Neutrons in the nucleus.
• The number of Protons Number of Electrons.
• Electrons orbit the nucleus in shells.
• Each shell can only carry a set number of
  electrons.

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ATOMIC STRUCTURE
Electrons are arranged in Energy Levels or Shells
around the nucleus of an atom.

• first shell a maximum of 2 electrons
• second shell a maximum of 8 electrons
• third shell a maximum of 8 electrons

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ATOMIC STRUCTURE
There are many ways to represent the atomic
structure of an element or compound. One of them
is
1. Electronic Configuration
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ELECTRONIC CONFIGURATION
With electronic configuration elements are
represented numerically by the number of
electrons in their shells and number of shells.
For example
Nitrogen
configuration 2 , 5
7
2 in 1st shell 5 in 2nd shell
N
2 5 7
14
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ELECTRONIC CONFIGURATION
Write the electronic configuration for the
following elements
20
11
8
O
Na
Ca
a)
b)
c)
16
23
40
2,8,8,2
2,8,1
2,6
17
14
5
Cl
Si
B
d)
e)
f)
11
35
28
2,8,7
2,8,4
2,3
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The Simplest Atom
Name Hydrogen
Atomic Symbol H
Mass Number (Number of Protons Neutrons) 1
Atomic Number (Number of Protons) 1
33
The Next Simplest Atom
Name Helium
Atomic Symbol He
The centre of an atom is called the NUCLEUS
A Helium atom has two protons and two neutrons in
its nucleus
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The Next Simplest Atom
Name Lithium
Atomic Symbol Li
The orbit nearest the nucleus can only contain 2
electrons
so the third electron must be in a new orbit.
Electron Configuration 2,1
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The Next Simplest Atom
Name Beryllium
Atomic Symbol Be
Electron Configuration 2,2
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The Next Simplest Atom
Name Boron
Atomic Symbol B
Electron Configuration 2,3
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Valence Electrons

• All the elements in a group have similar chemical
  properties as they have the same number of outer
  electrons which are called Valence electrons.
• For example Group 1 Li and Na.

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2.4
39
Atoms and the Periodic Table.

• We can classify (arrange) elements in different
  ways-

• naturally occurring/made by scientists

• solid/liquid/gas

• metal/non-metal

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NOTES The Periodic Table

1. The Russian scientist Dmitri Mendeleev published
   the first periodic table because he noticed a
   pattern of properties as he arrange elements by
   atomic mass.
2. Elements were rearranged by atomic number after
   the proton was discovered.
3. The properties of an element can be predicted
   from its location in the periodic table.
4. Each horizontal row of the table is called a
   period.
5. The elements in a column are called a group, or
   family.
6. The groups are numbered from Group 1 on the left
   to Group 18 on the right.

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Notes The Periodic Table

• Stars consist of matter in the form of plasma, a
  gas-like mixture .
• Elements are created when the extreme high
  pressure inside stars forces atomic nuclei to
  collide.
• This process is called nuclear fusion.
• Nuclear fusion combines smaller nuclei into
  larger nuclei creating heavier elements.
• Electrons are arranged in Energy Levels around
  the nucleus of an atom.
• They can hold 2 electrons in the first level, 8
  in the second and 8 in the third.
• The outer electrons are called Valence electrons,
  and each Group has the same number.

42
Metals

• The physical properties of metals include
• Shininess
• Malleability can be hammered or rolled into flat
  sheets and other shapes.
• Ductility can be pulled out, or drawn, into a
  long wire.
• Conductivity ability to transfer heat or
  electricity.
• Magnetic Attracted to magnets and can be made
  into magnets.
• Solids Most are, at room temperature.
• Corrosion Some metals react with oxygen in the
  air, forming rust.
• Reactive Combines with other elements with ease
  and speed. Metals usually react by losing
  electrons to other atoms. The reactivity of
  metals tends to decrease from left to right
  across the periodic table.

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Notes THE PERIODIC TABLE
METALS NONMETALS METALLOIDS
A substance or mixture that has a luster or shine, is generally a good conductor of heat electricity, is malleable ductile. They can corrode and can become magnetic. An element that does not exhibit the characteristics of a metal they are generally solids or gases and are usually hard, brittle substances. An element having both metallic and nonmetallic properties. They are usually good semiconductors
Except for mercury, the metallic elements are solids at room temperature (20 C) Bromine is the only liquid nonmetal.
44
Hydrogen

• Hydrogen belongs to a family of its own.
• Hydrogen is a diatomic, reactive gas.
• Hydrogen was involved in the explosion of the
  Hindenberg.
• Hydrogen is promising as an alternative fuel
  source for automobiles

45
Alkali Metals

• 1st column on the periodic table (Group 1) not
  including hydrogen.
• Very reactive metals, always combined with
  something else in nature (like in salt).
• Soft enough to cut with a butter knife

46
Alkaline Earth Metals

• Second column on the periodic table. (Group 2)
• Reactive metals that are always combined with
  nonmetals in nature.
• Several of these elements are important mineral
  nutrients (such as Mg and Ca

47
Transition Metals

• Elements in groups 3-12
• Less reactive harder metals
• Includes metals used in jewelry and construction.
• Metals used as metal.

48
Boron Family

• Elements in group 13
• Aluminum metal was once rare and expensive, not a
  disposable metal.

49
Carbon Family

• Elements in group 14
• Contains elements important to life and
  computers.
• Carbon is the basis for an entire branch of
  chemistry.
• Silicon and Germanium are important
  semiconductors.

50
Nitrogen Family

• Elements in group 15
• Nitrogen makes up over ¾ of the atmosphere.
• Nitrogen and phosphorus are both important in
  living things.
• Most of the worlds nitrogen is not available to
  living things.
• The red stuff on the tip of matches is phosphorus.

51
Oxygen Family or Chalcogens

• Elements in group 16
• Oxygen is necessary for respiration.
• Many things that stink, contain sulfur (rotten
  eggs, garlic, skunks,etc.)

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Halogens

• Elements in group 17
• Very reactive, volatile, diatomic, nonmetals
• Always found combined with other element in
  nature .
• Used as disinfectants and to strengthen teeth.
• Salt forming.

53
The Noble Gases
54
The Noble Gases

• Elements in group 18
• VERY unreactive, monatomic gases
• Used in lighted neon signs
• Used in blimps to fix the Hindenberg problem.
• Have a full valence shell.

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NotesThe Periodic Table (12 parts)
Hydrogen 1ve
Alkali Metals 1ve
Alkaline Earth Metals 2ve
Boron Family 3ve
Carbon Family 4ve
Transition Metals
Nitrogen Family 5ve
Oxygen Family 6ve
Halogens Family 7ve
Lanthanides
Noble Gases Family 8ve
Transition Metals, Lanthanides and Actinides have
different number of valence electrons.
Actinides
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Notes The Periodic Table

• Elements that follow uranium are made when
  nuclear particles are forced to crash into one
  another.
• Elements with atomic numbers above 92 are
  synthetic and are made in nuclear reactors or
  powerful machines called particle accelerators .
• Semiconductors are substances that under some
  conditions can carry electricity, and under other
  conditions cannot carry electricity.

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Links

• Webelements.comInteractive Periodic TableThe
  Visual Elements Periodic TableChemical
  ElementsLos Alamos National Laboratory
  Additional Physics Tutorials

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Radioactivity
59
Notes Radioactivity

1. In a process called radioactive decay, the atomic
   nuclei of unstable isotopes release fast-moving
   particles and energy.
2. In 1896, the French scientist Henri Becquerel
   discovered radioactive decay quite by accident
   while studying a mineral containing uranium.
3. Becquerel presented his findings to Marie Curie
   and her husband Pierre .The Curies concluded that
   a reaction was taking place with the uranium
   nuclei.
4. Radioactivity is the name that Marie gave to this
   spontaneous emission of radiation by an unstable
   atomic nucleus.
5. Natural radioactive decay can produce alpha
   particles, beta particles, and gamma rays.

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Notes Radioactivity

1. The particles and energy produced during
   radioactive decay are forms of nuclear radiation.
2. An alpha particle consists of two protons and two
   neutrons and is positively charged. It is the
   same as a helium nucleus. Alpha radiation can
   cause an injury much like a bad burn.
3. After alpha radiation the atomic number is
   decreased by 2 and the atomic mass by 4.
4. A beta particle is a neutron that changes into a
   proton and a negative beta particle. Beta
   particles can travel into the body and cause cell
   damage.
5. After beta radiation the atomic number increases
   by 1 and the atomic mass decreases by 1.
6. Alpha and beta decay are almost always
   accompanied by gamma radiation which is
   detectable.
7. Gamma radiation is high-energy waves. Gamma rays
   can pass right through the human body, causing
   severe cell damage.

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Notes Radioactivity

• Uses of radioactive decay include tracing the
  steps of chemical reactions and industrial
  processes, and diagnosing and treating disease.
• Tracers are radioactive isotopes that can be
  followed through the steps of a chemical reaction
  or an industrial process.
• In addition, the radiation given off by certain
  radioactive isotopes can be used to destroy
  unhealthy cells in the body, such as those in
  cancer tumors.
• Nuclear Decay Gizmo

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Notes Half-life

1. Half life
2. As a radioactive element within a rock or object
   decays, it changes into another element.
3. Therefore, the composition of the object changes
   slowly over time. The amount of the radioactive
   element decreases. But the amount of the new
   element increases.
4. The half-life of a radioactive element is the
   time it takes for half of the radioactive atoms
   to decay.

63
Notes Half-life

1. Scientists often use potassium-40 to date rocks.
   This form of potassium decays to form the stable
   element argon-40 and has a half-life of 1.3
   billion years. The long half-life of potassium-40
   makes it useful in dating the most ancient rocks.
2. Carbon-14 is useful in dating materials from
   plants and animals that lived as far back as
   50,000 years ago. Because carbon-14 has a
   half-life of only 5,730 years, it cant be used
   to date more ancient fossils or rocks.

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Notes Half-life

• Percentage What percentage of a radioactive
  element will be left after 3 half-lives? First,
  multiply ½ three times to determine what fraction
  of the element will remain.
• You can convert this fraction to a percentage by
  setting up a proportion
• To find the value of d, begin by cross
  multiplying, as for any proportion
• Practice Problems What percentage of a
  radioactive element will remain after
  5 half-lives?

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Links to radioactivity

• BrainPop Movie
• Nuclear Decay Gizmo
• Uses of Radiactivity