Docstoc

Chapter 3 Notes_ Atoms and Elements

Document Sample
Chapter 3 Notes_ Atoms and Elements Powered By Docstoc
					Chapter 3 Notes: Atoms and
         Elements
          1/23/13
                    Relevance
• Matter is made up of elements, compounds and
  mixtures and the atoms that make up these
  substances and how they interact determine how the
  materials’ properties

• The materials’ properties determine which item we
  would choose for a task, or why an object works the
  way it does.

• In order to understand the properties we need to
  understand the atoms of each element and how they
  interact.

                                                        2
                 Elements- 3.1
• Definition: Pure substances that is made up of
  only one kind of material. It can NOT be
  broken down into simpler substances

• Chemical symbols – 1 or 2 letter abbreviations
  for elements
  – only first letter is capitalized
     • ex. Fe, Ca, S, O, Pb
     • ex. CO = 2 elements: carbon – C and oxygen - O

                                                        3
                Examples
• What’s the symbol for these elements?
  – Mercury
  – Hydrogen
  – Chlorine
  – Nickel

• What’s the element name for these symbols?
  –   S
  –   Fe
  –   K
  –   Br
                                           4
        The Periodic Table- 3.2
• Grouped by similar properties and arranged
  by increasing mass

• Period – Horizontal Row in the Periodic Table
  (1-7)

• Group or Family – Vertical Column in Periodic
  Table (1A-8A or 1-18)
                                                  5
            Names of Groups
• Representative elements (1A-8A) or (1,2 + 13-
  18)
• Transition Elements: in the middle between
  Group 2 and 13 (labeled w/ B)
• Alkali Metals: Group 1 (1A)
• Alkaline Earth Metals: Group 2 (2A)
• Halogens: Group 17 (7A)
• Noble Gases: Group 18 (8A)
                                                  6
                    Metals
• Metals: Mainly to left of zig-zag line
  – shiny solids,
  – ductile (pulled into wires),
  – malleable (hammered into sheets),
  – good conductors of heat and electricity,
  –  usually melt at higher temperatures than
    nonmetals
  – solids at room temperature (except mercury
    which is a liquid)
                                                 7
                  Nonmetals
• Nonmetals- to the Right of zig-zag line
  – not shiny
  – not ductile
  – not malleable
  – often poor conductors of heat and electricity
  – low melting points and densities (usually)




                                                    8
                         Metalloids
• Elements on zig-zag line (B, Si, Ge, As, Sb, Te, Po,
  At)
   – some properties of metals and nonmetals
   – ability to conduct heat and electricity
      • metals > metalloids > nonmetals
   – Semiconductors
      • in electronics
• Table 3.4 and picture below show amounts of
  essential elements in human body
   – Mainly H, C, O, N, microminerals: P, S, Cl, Na, Mg, K,
     Ca

                                                              9
                The Atom – 3.3
• Atom- smallest particle of an element

• Dalton’s Atomic Theory (1808)
  – All matter is made up of tiny particle called atoms
  – All atoms of a given element are similar to one
    another and different from atoms of other elements
  – Compounds = combinations of atoms of 2 or more
    different elements.
     • A given compound always has same kind of atoms and
       number of atoms of each element
  – A chemical reaction involves the rearrangement,
    separation, or combination of atoms.
     • Atoms are never created or destroyed in a chemical
       reaction.
                                                            10
    Charge and Structure of atom
• Atoms are electrically neutral (equal + and –
  charges)
• Electrons = small negative charges (J.J. Thompson
  1897)
• Protons = positive charges
• Plum pudding model -> electrons floating
  randomly in proton jello
• Rutherford 1911 gold foil experiment –Phet
• Predictions based on plum pudding model?

                                                  11
             Structure of the atom




http://water.me.vccs.edu/courses/ENV295Labs/changes/atom2.jpg
                                                                12
              Mass of an atom
• Mass of protons, neutrons and electrons in
  grams is very small. ( 1.7 x 10-24 g, 1.7 x 10-24 g,
  9.1 x 10-28 g)
• Use amu (atomic mass units) instead
• amu = 1/12 mass of carbon atom w/ 6 protons
  and 6 neutrons




                                                     13
 Atomic Number and Mass Number –
               3.4
• All atoms of an element have same number of
  protons
  – can tell elements apart by number of protons
• Atomic number = number of protons in an
  atom
• Mass number = number of protons and
  neutrons in an atom
• In a neutral atom; number of protons =
  number of electrons
                                                   14
                    Examples- Atoms
 Name      Symbol    Atomic    Mass    Number of   Number of   Number of
                     Number   Number    protons     neutrons   electrons
             H
Nitrogen
                       8
Sodium
             Al
  Iron




                                                                  15
  Isotopes and Atomic Mass – 3.5
• Isotope = atoms of the same element with the
  same atomic number but a different numbers of
  neutrons
• Atomic mass is a weighted average of the masses
  of the different isotopes
• example: 2412Mg; 24 = mass number, 12 =
  atomic number
  – also known as Mg-24
  – Examples carbon-12, C-14 -> used for dating fossils

                                                          16
                 Examples - Isotopes
Symbol      Name of   Atomic   Mass     Number    Number     Number
            element   Number   Number   Protons   Neutrons   Electrons
     10Ne
20


     6C
14

O-18




                                                                     17
     Calculating Atomic Mass using
                Isotopes
• Atomic Mass of element = sum of ( mass
  isotope1 * % abundance isotope1/100 + mass
  isotope2 * % abundance isotope2/100 etc)

• Example:
  – Cl-35, mass = 34.97; % abundance = 75.76%
  – Cl-37, mass = 36.97; % abundance = 24.24%
• What’s the average atomic mass of Chlorine?
                                                18
                 Example
• Given the mass and % abundance of the three
  isotopes of Magnesium, what is the average
  atomic mass of magnesium?
     Isotope     Mass      % abundance
      Mg-24      23.99       78.70%
      Mg-25      24.99       10.13%
      Mg-26      25.98       11.17%




                                            19
 Electronic Arrangement in Atoms 3.6
• Protons and neutrons in nucleus.
• Electrons arranged in large volume of space
  around nucleus

• Energy Level – space with a specific energy that
  an electron can occupy
  – Each energy level has principal quantum number (n),
    goes 1-7
     • smaller numbers = closer to nucleus
     • Less energy to fill lower energy levels vs. higher ones (larger
       numbers)


                                                                     20
21
             Electron Sublevels
• Sublevels – levels within energy levels where
  electrons of the same energy reside
  – s, p, d, f – identifies sublevels




                                                  22
                     Orbitals
• Orbital – area of high probability of finding an
  electron.
  – s, p, d, f have different shapes


• Mainly deal with knowing shapes for s and p
  orbitals



                                                     23
s orbitals




             24
p orbitals




             25
d orbitals




             26
  Maximum Number of electrons for
          each subshell
• s subshell = 1 orbital = 2 electrons

• p subshell = 3 orbitals = 6 electrons

• d subshell = 5 orbitals = 10 electrons

• f subshell = 7 orbitals = 14 electrons

                                           27
28
       Orbital Diagrams and Electron
            Configurations – 3.7
• Electron configuration-
  shows the placement of
  the electrons in the
  orbitals in order of
  increasing energy

• Orbital Diagram – fill in
  boxes representing
  orbitals
   – each orbital holds a
     maximum of 2 electrons
   – Fill lowest energy first
   – Electrons represented by
     arrows; paired arrows go
     in opposite directions
                                       29
30
                 Example
• Draw Orbital diagram for Carbon
• Number of electrons in Carbon atom?
• Which subshells are filled?




                                        31
        Electron configurations
• Uses coefficients, letters and subscripts to
  describe placement of electrons in order of
  increasing energy

• Example: Nitrogen 7 electrons
  – 1s2 2s2 2p3
  – coefficient = row number
  – letter = type of orbital
  – exponent = number of electrons in that orbital

                                                     32
                 Examples
• Write electron configuration for Carbon

• Draw orbital diagram for Nitrogen

• Write electron configuration for Aluminum

• Draw orbital diagram for Aluminum

                                              33
Abbreviated Electron configuration
• Electron configurations can be long to write
  especially for elements farther down in periodic
  table

• Use abbreviated electron configurations instead.
  – Use noble gas that’s before element on interest in
    square brackets then rest of electron configuration
  – Ex. Aluminum 13 electrons
     • [Ne] 3s2 3p1
     • [Ne] accounts for first 10 electrons

                                                          34
                 Examples
• Write the electron configuration and the
  abbreviated electron configuration for the
  following elements
• P
• O
• Br
• Ca
• Fe
                                               35
Trends in Periodic Properties – 3.8
• Valence Electrons = electrons in the outermost energy
  level of an element
    – are responsible for the chemical properties of an element
    – Group number w/ A in it = number of valence electrons for
      that column.

 Group      1    2      13     14     15      16     17     18
Number
 Group      1A   2A     3A     4A     5A      6A     7A     8A
Number
  w/ A
Number      1    2      3       4      5      6       7      8
    of
 Valence
Electrons
                                                              36
                 Examples
• How many valence electrons do the following
  atoms have?
• Chlorine
• Boron
• Calcium
• Hydrogen
• Carbon
• Phosphorous
• Selenium
                                                37
                   Atomic Size
• Atomic size is determined by its atomic radius
• Atomic radius = distance between valence
  electrons and the nucleus
  – Increases going down a column (group or family)
     • valence electrons get farther from nucleus
  – Decreases going across a row L to R (period)
     • number of protons increases (positive charge
       increases) pulls on negatively charged electrons more


                                                               38
Atomic Size/Radius Trend




                           39
                 Examples
• Which has a larger atomic radius?

• Aluminum or Calcium

• Phosphorous or Silver (Ag)

• Iron or Nitrogen

                                      40
        Ionization Energy Trend
• Ionization Energy – Energy needed to remove
  the LEAST tightly bound electron from the
  atom
  – decreases going down a column (group/family)
     • outer electrons are farther from nucleus, less tightly
       held
  – increases going across a row L to R (period)
     • positive charge in nucleus increases because of extra
       protons; more tightly holds negatively charged
       electrons


                                                                41
Ionization Energy Trend




                          42
                 Examples
• Which has the larger ionization energy?

• Potassium or Oxygen

• Cobalt (Co) or Chlorine

• Barium or Fluorine

                                            43
             Metallic Character
• Metals tend to lose electrons and make cations
  – cations = positive ion

• Nonmetals tend to gain electrons and make
  anions
  – anions = negative ion

• Metals are on Left of periodic table
• Non metals on Right of periodic table

                                                   44
                 Examples
• Label each of the elements as metals,
  metalloids, or nonmetals
• Sodium
• Sulfur
• Boron
• Oxygen
• Iron
• Selenium

                                          45

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:1
posted:7/9/2013
language:English
pages:45