Atoms and The Periodic Table

1
Atoms and The Periodic Table

• Chapter 3 p. 70
• Blue Book
• Objectives for this chapter
• 1) Understand the history of how early scientists
  discovered the atom.
• 2) To understand the structure of an atom and be
  able to classify the three main subatomic
  particles according to their location and charge.
• 3) Understand and know how to figure half- life
  of substances.
• 4) Be able to describe the design of the modern
  periodic table.
• 5) Understand and know certain elements from the
  periodic table.
• 6) Know and be able to explain certain vocabulary
  words.

2

• History of Matter
• Greeks 2500 yrs. Ago
• Had the idea that all matter was composed of 4
  elements fire, air, water and earth (but this
  didnt make sense).
• Decades later had the idea take matter cut in
  half, again again.
• Eventually you couldnt cut it anymore
• One particle left was named atoms a small
  particle that makes up most types of matter.
• term means cannot be divided
• IE string of beadsend with one bead.
• Eighteenth century atom discussion restarted.
• Studied matter in laboratoriesdetermined that
  different types of atoms existed for every type
  of matter and that the atoms identity explained
  the characteristic of each type of matter.
• Found out that matter is anything that has mass
  and takes up space. Made of
• elements cannot be broken down into simpler
  substances

3

• John DaltonEnglish teacher.
• He combined element idea with atom idea from
  Greeks.
• He proposed
• matter is made of elements
• atoms cannot be divided into smaller pieces
• all atoms of an element are alike
• atoms are hard spheres the same throughout
  like a marble

4

• William Crookes1870better equipment to
  experiment with.
• Cathode Ray Tube CRT (p. 76)
• Found negatively charged particles.
• JJ Thomson
• Repeated CRT with different metalssame result
• http//highered.mcgraw-hill.com/olcweb/cgi/pluginp
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  512644/117354/01_Cathode_Ray_Tube.swfCathode20R
  ay20Tube
• Negatively charged particlesnow called
  electrons
• Why isnt all matter negatively charged then?
• Is there something that neutralizes the negative
  particles?
• Evidence of a positive charge was found in 1920.
• Scientists identified the proton positive
  charged particle
• 2000 times heavier than the electron

5

• - Ernest RutherfordRutherfords Atom (p. 77)
• - Wanted to test Thomsons model of the atom
• He bombarded a thin sheet of gold with alpha
  particles 2 protons 2 neutrons
• These come from unstable atoms have a positive
  () charge
• He expected most alpha particles would pass right
  through the gold foil.
• Why? he hypothesized there was not enough
  matter to change path
• BUTmore particles bounced and angled off than
  expected.
• Some bounced back p. 77
• Conflicted with cookie dough model.
• Thereforehe proposed almost all the mass of the
  atom was in a very small region in the center of
  the atom.

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• This area is now called the nucleus
• Center of the atom that contains the protons and
  neutrons
• The rest of the atom is empty space occupied by
  electrons
• Summary HOW did Rutherford find the nucleus?
• The alpha particles hit center bounced/
  repelled off

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• Other scientists reviewed data and reasoned that
  since electrons have no mass, most mass of the
  atom should then be equal to protons.
• BUT, it isnt
• Mass of most atoms is twice that of its protons.
• Where does this extra mass come from?
• Rutherford reasoned there must be another
  particle in nucleus
• Today we know this as the neutron
• neutral charged particle
• same mass as proton
• took 20 yrs to find and prove the existence of
  the neutron

8

• Atom size?
• There are roughly 1 trillion atoms in a period at
  the end of a sentence
• Where are the electrons?
• Electrons go around nucleus somewhere
• They dont know precise location at a certain
  momentelectrons are constantly moving.
• Niels Bohr model electrons are arranged
  according to energy levels.
• Lowest energy levels are close to nucleus.
• Highest energy levels are farthest from nucleus
• Thereforeelectrons are located in a region
  around the nucleus called
• the electron cloud

9
Matter Timeline

• Identify 12 main/important events in the
  discovery of matter.
• What year did they happen?
• Who was involved?
• Using a unique shape (not just a line), map out
  the 12 events from first to most recent.
• Add a picture to illustrate each event.

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• What makes atoms different from each element?
• Atomic number number of protons
• Listed on Periodic Table main number at top
• Increasing from 1 - 116
• Atoms of the same element ALWAYS have the same
  number of protons
• Thereforeprotons make different elements
• Proton Atomic
• What else equals the proton number? ELECTRONS!
• Size of Nucleus? (p. 77)
• If the nucleus was the size of a poppy seedatom
  would be the size of a football stadium!
• Atomic SummaryThree Main Subatomic Particles
• 1) proton positive () nucleus .
• 2) neutron neutral () nucleusN
• 3) electron negative (-) electron cloude-
• Which particle is the most important in
  determining the type of element?
• proton
• If you change proton , you change the element

11

• Atomic Number number at top of square.
• Atomic Symbol
• Element Name
• Atomic Mass
• P _____ (same as atomic number)
• N _____ (Atomic mass atomic number)
• E _____ (same as protons)

12

• How to draw Bohrs Diagram
• Find the element on the periodic table.
• Determine the number of electrons (same as atomic
  number)
• The number of electrons is how many you will draw
  in Bohrs model.
• With your element in the center, draw a circle
  around your nucleus.
• The first circle can only have 2 electrons
• The second circle can only have 8 electrons.
• The third circle can only have 18 electrons.

13

• Carbon has 6 electrons
• The first shell has 2
• Since you already have 2, you only need to draw 4
  more (246)

14

• - What about the neutron ? Can it change?
• YES Isotope atoms of the same element that
  have a different of neutrons
• IE - Carbon 12
• Carbon13
• Carbon 14
• Number of protons? same
• Number of neutrons? different
• - Mass number of protons neutrons
• - Atomic number of protons
• Holding protons in nucleus?
• strong nuclear force nuclear glue
• not fully understoodDiscuss

15

• - If isotope has too many or too few neutrons, it
  can be unstable and it may go through
• - Radioactive Decay release of nuclear particles
  and decay
• when particles are ejected from nucleus
• atomic can change therefore the element can
  change
• Transmutation changing of one element into
  another element through radioactive decay

16

• Some radioactive isotopes release
• 1) alpha particle 2 protons and 2 neutrons
• 2) beta particle high energy electron
• - Half Life (radioactive isotope) amount of
  time it takes for half of a sample of the element
  to decay
• convenient way to measure the rate of decay of a
  nucleus
• unaffected by conditionsweather, pressure,
  electric or magnetic currents, chemical reactions
• rate of time is different for each isotopefrom
  secondsto billions of years!
• IE If half life is 1 yr. 1000 g sampleleft
  after 3 yrs.?
• Carbon datingC14 5730 yrs. (p. 51)
• Living things have certain amount of carbon
• Find fossilrelate amount of carbon back to when
  it was livingHalf 5730yrs.!!
• http//www.youtube.com/watch?v31-P9pcPStg

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• Periodic Table
• Early civilizationsfamiliar with a few of the
  elements.
• Coins and jewelry from gold
• Battle of Troyarmor from bronze (copper tin)
• Assyrians built empire with weapons of steel
  (iron carbon)
• Nineteenth centurybegan search for new elements
• 1830 had isolated and named 55 different
  elements
• 1860 Russian chemist Dmitri Mendeleev
• used knowledge to build a table of elements
• arranged in order of increasing atomic mass
• He began to see a pattern.
• Elements with similar properties fell into
  groups.
• Published first periodic table in 1869

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• Even though all elements werent knownMendeleev
  predicted missing elements and left gaps for
  undiscovered elements
• Early 20th century, English physicist Henry
  Moseley
• Improved Mendeleevs table by arranging the
  elements in order of increasing atomic number.

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• Modern Periodic Table
• Arranged in increasing atomic number
• Rows or periods
• row of elements on the periodic table whose
  properties change gradually and predictably
• Columns group or family
• contains elements that have similar physical or
  chemical properties

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• Color coded? Different colors
• (88) metals element that has luster and is a
  good conductor of heat and electricity and is
  malleable
• (luster ability to reflect light)
• (16) nonmetals gases or brittle solids at room
  temperature, poor conductor of heat and
  electricity
• (8) metalloids shares properties of both metals
  and nonmetals
• IE boron has a luster, but is a poor conductor

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• Element Keys
• Each element box on the periodic table contains
• Element name (Some do not)
• Atomic number
• Symbol
• Average atomic mass
• Bulls eye symbol not naturally on Earth
• Synthetic man made
• Others are labeled according to key - solid,
  liquid or gas at room temperature
• Most stable elements are right column of table
  all gases
• Symbols dont make sense? gold Au
• due to Latin or Greek origin
• some new names geographic areas, names,
  countries
• Unnamed IE - Uun, Uuu, Uub
• temporary name