Chapter 3: Atoms

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Chapter 3 Atoms the Periodic Table
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These are uranium atoms. What do they look
like? What actually are you seeing?
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Section 1 Inside an Atom

• Structure of an Atom
• An atom consists of a nucleus surrounded by one
  or more electrons.
• The nucleus is the tiny, central core of an atom

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• An atom has 3 types of particles
• (subatomic particles)
• Protons -- have a positive electric charge are
  located in the nucleus
• Neutrons -- have a neutral electric charge are
  located in the nucleus
• Electrons -- have a negative electric charge
  are located outside of the nucleus

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The atoms nucleus contains protons and neutrons.
The high energy electrons move in the space
around the nucleus called the electron cloud.
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Atomic Number the number of protons in a nucleus

• Is a unique property that identifies the element
• Ex Every Carbon atom has 6 protons
• In an atom, the of protons the of electrons
  are equal, making the atom neutral.

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Atomic Mass the average mass of one atom of an
element

• Since atoms are so small, they are measured in
  atomic mass units (amu).
• The mass of a proton or a neutron is about one
  amu.
• Electrons are much smaller.

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• It takes almost 2000 electrons to equal one amu!
• Therefore, most of an atoms mass is in the
  nucleus of an atom.
• Ex An atom that has 6 protons, 6 neutrons, and 6
  electrons has a mass of about 12 amus

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• The number of protons in an element does not
  change
• the number of neutrons can change. (Isotopes of
  an atom)
• Ex Carbon atoms always have 6 protons. But
  they may have 5,6,7,or 8 neutrons. (Isotopes of
  carbon)
• This means that the amu will vary.

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• Since neutrons dont play a role in chemical
  reactions, the chemical properties of each
  element are the same despite having different
  masses.

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The Role of Electrons

• Electrons move around the nucleus so fast that it
  is impossible to know exactly where any electron
  is at a particular time!
• Its like a spherical cloud of negatively charged
  electrons.

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Imagine the blades of a moving fan.
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Little Particles, Big Spacesvideo

• The space in which electrons move is HUGE!!!
• Ex Imagine standing at the pitchers mound in a
  baseball stadium. If the nucleus were the size
  of a pencil eraser, the electrons could be in the
  outfield or the top row of seats!

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• So, what composes the majority of an atoms mass?
• What composes the majority of an atoms volume?

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Valence Electrons

• Electrons in an atom are not all the same
  distance away from the nucleus.
• Valence electrons are those that are the farthest
  away.

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• A chemical bond forms between 2 atoms when
  valence electrons move between them.
• Valence electrons may be transferred from one
  atom to another, or they may be shared between
  atoms.

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• The number of valence electrons can vary from 1
  to 8.
• Each element has a typical of valance
  electrons.
• Ex Oxygen has 6, Carbon has 4, Hydrogen has 1

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Electron Dot Diagrams

• Used to represent valence electrons.
• A symbol for an element is surrounded by dots.
  Each dot stands for one valence electron.

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• When atoms have 8 or 0 valence electrons, the
  atom becomes more stable- or less reactive than
  they were before.

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Models of Atoms

• 1808- Dalton Model
• each element is made of small atoms different
  elements have atoms of different masses
• atoms similar to tiny, solid balls

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Models of Atoms

• 1897-Thomson Model
• Atom is a positively charged sphere with
  electrons embedded in it.
• Similar to a muffin w/ berries scattered through
  it

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THOMPSONS MODEL
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Models of Atoms

• 1904- Nagaoka Model
• Atom had a large sphere in the center with a
  positive charge.
• Electrons revolved around the sphere like
  planets revolve around the sun.

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Models of Atoms

• 1911-Rutherford Model
• Atom is mostly empty space.
• Electrons orbit randomly around a small,
  positively charged nucleus.

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RUTHERFORDS MODEL
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Rutherfords Experiment - showed that particles
were deflected by something in atoms. He deduced
that this was a positively charged nucleus.
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Models of Atoms

• 1913-Bohr Model
• Electrons move in specific layers, or shells
• Atoms absorb or give off energy when the
  electrons move from one shell to another

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BOHRS MODEL
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Models of Atoms

• 1932-Chadwick Model
• Discovered the neutron.
• The existence of the neutron explained why atoms
  were heavier than the total mass of their protons
  and electrons.

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Models of Atoms

• 1920s to Present- Modern Model
• Electrons form a negatively charged cloud around
  the nucleus.
• Its impossible to determine the exact location
  of an electron

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Section 2 Organizing the Elements
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The Periodic Table

• Mendeleev patterns appeared when the elements
  were arranged in order of increasing atomic mass.
• Sometimes this method didnt work, so he would
  put the elements in a best fit location.

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Modern Periodic Table

• Based on atomic number (discovered in the 1900s)
  rather than atomic mass
• the properties of the elements repeat in each
  period (row) of the table

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This is Henry Mosley, a British scientist. He
created the modern periodic table of elements by
placing the elements in order of their atomic
number instead of mass. (He was only 27 years
old when he was killed in WWI.)
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Reading the Periodic Table

• Each square of the table usually includes the
  elements atomic number, chemical symbol, name,
  and atomic mass.

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Elements Name
Atomic Number
Elements Symbol
Atomic Mass
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An elements properties can be predicted from its
location in the periodic table!
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Organization of the Periodic Table

• Main body of table has 18 vertical columns 7
  horizontal rows
• The elements in a column are called a group
• Groups are also known as families

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Group Numbers
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• The elements in each group, or family, have
  similar characteristics.
• Ex elements in group 1A are all metals that
  react violently with water. Elements in group 18
  rarely react at all

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• Each horizontal row across the table is called a
  period
• Elements in a period have very different
  properties
• As you move across a period from left to right,
  those properties change according to a pattern

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Periods
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Why the Periodic Table Works

• Because it is based on the structure of atoms,
  especially the valence electrons.
• Elements in a family all have the same number of
  valence electrons
• This is a reason why the elements in a particular
  group have similar properties

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• As you move from left to right across a period,
  the atomic number increases by one
• This means that an element has one more valence
  electron than the element to its left

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Section 3 Metals
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• Physical properties of metals
• hardness,
• shininess,
• malleability (can be pounded or rolled into
  shapes) ,
• ductility (can be pulled out or drawn into wires)

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• Most metals are good conductors because they
  transmit heat and electricity easily
• Several metals are magnetic (attracted to
  magnets)--iron (Fe), cobalt (Co), and nickel (Ni)
• Most metals are solids at room temperature ( they
  have a high melting point)
• exception is mercury(Hg)--liquid at room
  temperature

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Chemical Properties of Metals

• Metals have a wide range of chemical properties
• Some are very reactive sodium (Na), potassium
  (K)
• Some are unreactive gold (Au) and chromium (Cr)

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• Some metals are in the middle. These metals
  react slowly with oxygen in the air, forming
  metal oxides
• Ex Iron left unprotected will slowly rust (turn
  a reddish brown)
• Process of reaction and wearing away Corrosion

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Alloys

• Alloy a mixture of metal (Remember a mixture
  consists of 2 or more substances mixed together
  but not chemically changed)

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• Some common alloys
• Copper Tin Bronze
• Copper Zinc Brass
• Iron Carbon Chromium Vanadium Stainless
  Steel
• Gold Silver Copper a little Zinc Yellow
  Gold
• Gold Nickel Copper Zinc White Gold

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Metals in the Periodic Table

• The metals in a group, or family, have similar
  properties, and these family properties change
  gradually as you move across the table.

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Alkali Metals

• Metals in Group 1- from Li to Fr
• These are the most reactive metals since they
  only have 1 valence electron
• In nature, these are never found as
  elements--exist only as compounds

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• As elements, they are very soft shiny
• Most important alkali metals are
• Sodium (Na)
• Potassium (K)

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Alkaline Earth Metals

• Group 2 alkaline earth metals
• Not as reactive as Group 1 but they are more
  reactive than most metals
• Never found uncombined in nature
• They have 2 valence electrons

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• Most common alkaline earth metals
• magnesium (Mg) -- used to be in flash bulbs
  because of the very bright light
• calcium (Ca) --important in bones and teeth

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Transition Metals

• Elements in group 3 - 12 are the transition
  metals
• These metals form a bridge between the reactive
  metals on the left to the less reactive metals on
  the right

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• Example of transition metals
• iron, copper, nickel, silver, and gold
• Most are hard and shiny
• All are good conductors of electricity
• Are fairly stable, reacting slowly or not at all
  with air and water

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Metals in Mixed Groups

• Groups 13 - 16 include metals, nonmetals, and
  metalloids
• Not as reactive as the metals in groups 3 - 12
• Ex aluminum, tin, and lead

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Lanthanides Actinides

• At the bottom of the periodic table,
• the top row Lanthanides
• bottom row Actinides
• These elements are called the rare earth elements
  they fit in Periods 6 7

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• Lanthanides soft, malleable, shiny metals w/
  high conductivity
• Actinides
• only thorium and uranium exist on Earth in
  significant amounts
• All the elements after uranium were created
  artificially in the lab
• the nuclei of these elements are very unstable
  (many last for only a fraction of a second after
  they are made)

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Section 4 Nonmetals Metalloids

• Nonmetals elements that lack most of the
  properties of metals
• The 17 nonmetals are to the right of the zig zag
  on the periodic table

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• In general, nonmetal physical properties are
  opposites of metal properties. Most nonmetals
  are
• Dull,
• Solid nonmetals are brittle (not malleable or
  ductile)
• Poor Conductors of heat electricicity

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Chemical Properties of Nonmetals

• Most nonmetals form compounds easily EXCEPT those
  from Group 18 (Noble Gases)
• Reason group 18 doesnt gain, lose, or share
  electrons with other elements. Why?

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Compounds of Nonmetals

• When nonmetals and metals react, valence
  electrons move from the metal atoms to the
  nonmetal atoms. (See pg 99)
• Table Salt Na (metal) Cl (nonmetal)

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• How many valence electrons does Na (sodium) have?
• How many valence electrons does Cl (chlorine)
  have?
• Are valence electrons shared or transferred to
  make NaCl?
• Which element transferred the valence electron in
  order to make table salt?

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How many valence electrons does Hydrogen have?
Chlorine? Are the valence electrons transferred
or shared? by whom?
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• Nonmetals can also form compounds with other
  nonmetals
• The atoms share electrons and become bonded
  together into molecules.
• Diatomic moleculesmolecules have only 2 atoms
• Ex Oxygen (O2), Nitrogen (N2), and Hydrogen (H2)

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Diatomic molecule of H2 (Hydrogen)
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Families of Nonmetals

• Carbon Family (Group 14)
• Each element has 4 valence e-
• Carbon nonmetal
• Silicon Germanium metalloids
• Tin Lead metals

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• Nitrogen Family (Group 15)
• Each element has 5 valence e-
• Nonmetals
• N Nitrogen gas is 80 of the air
• P always found in compounds
• As Sb metalloids
• Bi metal

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• Oxygen Family (Group 16)
• Each element has 6 valence e-
• Usually gain/share 2 e- when they react
• Nonmetals
• Oxygen very reactive can combine with most
  elements most abundant element in Earths crust
  2nd in the atmosphere

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• Sulfur strong, unpleasant odor in rubber bands,
  car tires, medicine
• Selenium
• Metalloid Tellurium
• Metal Plonium

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• Halogen Family (Group 17)
• All except Astatine are nonmetals
• All have 7 valence e-
• Typically gain/share 1 valence e-
• All are very reactive most are dangerous to
  people
• Fluorine most reactive nonmetal found in
  nonstick cookware toothpaste

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• Chlorine used in table salt (NaCl), and used to
  melt snow (CaCl)
• Bromine when with Silver (AgBr) used in
  photographic film

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• Noble Gases (Group 18)
• Do not usually form compounds since some dont
  gain/lose/share their valence e-
• All exist in the atmosphere but in small amounts
• Can be found in glowing electric lights (neon
  lights) but are filled with Ar, Xe, or other
  noble gases

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• Hydrogen
• Simplest element (usually 1 proton 1 electron)
• Since chemical properties are so different from
  other elements, it cant really be put into a
  family
• 90 of the atoms in universe
• 1 of the mass of Earths crust, oceans, and
  atmosphere

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• Hydrogen usually found on Earth as a compound
  (combined with oxygen in water)

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Metalloids

• 7 of them on the border between metals and
  nonmetals
• Have similar properties as the metals and
  nonmetals

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• Silicon (Si) is the most common
• when combined with Oxygen, it can form sand,
  glass, and cement
• Most useful property is their varying ability to
  conduct electricity
• it would depend on temperature, exposure to
  light, or impurities

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• The varying ability to conduct electricity is why
  these elements are used to make semiconductors
• Semiconductorssubstances that under some
  conditions can carry electricity, while under
  other conditions cannot carry electricity
• Semiconductors are used to make computer chips,
  transistors, lasers

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Section 5 Elements from Stardust

• Atomic Nuclei Combine
• Sun is made mostly of H which exists at high
  temp(15 million degrees Celsius) pressure (This
  state of matter plasma)
• Plasma atoms are stripped of their electrons,
  the nuclei are packed close together

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• Usually positively charged nuclei repel each
  othen stars (the plasma state)nuclei are close
  enough and moving fast enough to collide with one
  another
• In Nuclear Fusion, atomic nuclei combine to form
  a larger nucleus, releasing huge amounts of energy

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• Inside stars, nuclear fusion combines smaller
  nuclei into larger nuclei, thus creating heavier
  elements
• Think of stars as element factories

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• Elements from the Sun
• When 2 hydrogen nuclei with neutrons join
  together, they produce a helium nucleus.
  Releasing a lot of energy
• This reaction is a major source of the suns
  energy
• Estimate that the sun has enough hydrogen to last
  another 5 billion years

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• As helium builds up, the volume temp of suns
  core changes. This allows different nuclear
  fusion reactions to occur
• Stars the size of the sun do not contain enough
  energy to produce elements heavier than oxygen

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• A very massive star can explode (a supernova)
  providing enough energy for nuclear fusion
  reactions that create the heaviest elements.
• Theory Matter in the sun planets around it
  originally came from a gigantic supernova that
  occurred billions of years ago