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Periodic trends detailed edit
 

Periodic trends detailed edit

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    Periodic trends detailed edit Periodic trends detailed edit Presentation Transcript

    • Periodic Trends
      Chapter 6 Section 3
      pp.163-169
    • What is a trend?
      1. The general direction in which something tends to move.
      2. A general tendency or inclination. See Synonyms at tendency.
    • Things to remember…
      An element’s # of protons does not change
      Isotopes- atoms of an element with different masses.
      Different number of neutrons
      Nuclear charge- over all charge obtained from the attraction of all the protons and all e- in an atom
      Positively charged nucleus pulls electrons towards it
    • Ions
      An atom or bonded group of atoms that has a positive or negative charge
      Occurs when an atom gains or loses an electron
      Atoms that gain e- have a negative overall charge (anion)
      Atoms that lose e- have a positive overall charge (cation)
      Electrostatic repulsion
      Remember like charges repel each other…electrons in orbitals repel/push each other away
    • Ionization Energy
      Ionization energy (IE) is the energy required to remove an electron from a gaseous atom (kJ/mol)
      Energy is needed to overcome the attraction between the positive protons and negative electrons
      IE indicates how strongly a nucleus can hold onto its valence e-
      High IE= strong hold on e-; less likely to make positive ions
      Low IE= atom can lose valence e- easily; likely to make positive ions
    • Octet Rule
      What is the electron configuration for sodium?
      What is the new configuration when a sodium atom becomes a +1 sodium atom?
      What noble gas does this configuration look like?
      OCTET RULE:
      Atoms tend to gain, lose, or share electrons in an order to acquire a full set of 8 valence electrons
      First period elements are en exception to the rule (2Ve-)
      This rule helps to determine what kind of ions will form
    • More about ionization energy…
      1st Ionization Energy (1st e-)
      After removing the 1st e- it is still possible to remove additional electrons
      Second ionization energy:
      The IE needed to remove a second electron from a +1 ion
      For sodium IE will be high since it does not want to lose anymore e-, reached 8 valence e-
      Third ionization energy:
      The IE needed to remove a third electron from a +2 ion
      1e-
      8e-
      11p+
      12n
      2e-
      Sodium
    • Ionization Energy
      What type of IE does group 1A have? High or low?
      Low IE
      Likely to form + cations
      What type of IE does group 8A have?
      High IE
      Unlikely to form cations
      From left to right, the IE to remove successive electrons always increases
      Does not happen smoothly…requires large jump of energy
    • IE continued….
      Trends in periods:
      First IE generally increases as you move left-to-right
      The nuclear charge increases (greater attraction) with each successive element…
      What does this have to do valence electrons?
      Increase the nuclear charge=stronger hold on valence electrons
    • IE continued…
      Trends within groups…
      First IE generally decrease as you move down a group
      What happens to the size of an atom as you move down a group?
      Increases
      This cause decrease in IE
      Valence electrons are farther from the nucleus
      Easier to remove
    • Electronegativity
      The ability of atoms of an element to attract electrons in a chemical bond
      Fluorine is the most electronegative element
      Value: 3.98
      Cesium and Francium are the least electronegative
      Values: 0.79 and 0.7
      Atom with greater electronegativity attracts electrons in a chemical bond the strongest
      Leave out noble gases (they really don’t react)
    • Electronegativity (EN)
      Trends in periods and groups:
      EN decreases as you move down a group
      Increases as you move left to right on table
      Where are the lowest electronegatives found?
      Lower left side of the periodic table
      Where are the highest electronegatives found?
      Upper right side of the periodic table
    • Electron Affinity
      The energy change that occurs when an electron is acquired by a neutral atom
      Measure in kJ/mol
      High Eaffinity = more negative the nrg, easier to gain e-
      Low Eaffinity = more positive the nrg, easier to lose e-
      Noble gases have “zero” Eaffinity
    • Electron Affinity
      Many atoms release energy when they gain an electron
      A + e-  A- + energy
      A + e- + energy  A-
      Some atoms need energy to be “forced” to gain an electron
      Produces unstable ions that lose electron quickly
    • Food for thought….
      Do atoms on the right side of the periodic table tend to gain or lose electrons?
      Gain electrons
      What type of ions are they likely to form?
      Negative ions
      Do atoms on the left side of the periodic table tend to gain or lose electrons?
      lose e-
      What type of ions do they form?
      Positive ions
    • Atomic Radius
      Electron cloud
      Spherical surface in which there is a 90% probability of finding an e-
      Not physical
      Atomic size is defined by how closely an atom lies to its neighboring atom
      Each atom has different properties so there are going to be different sizes…
      Different sizes in different blocks…
    • Atomic Radius of a Metal
      Metals
      Atomic radius
      half the distance between adjacent nuclei in a crystal of that element
    • Atomic Radius of a Nonmetal
      Usually occur as molecules
      Atomic radius:
      Half the distance between nuclei of identical atoms that are chemically bonded together
      Diatomic molecules
      Hydrogen
      Bromine
      Iodine
      Oxygen
    • Atomic Radius: Trends in Periods
      DECREASE in atomic radii left-to-right
      Increasing positive charge in the nucleus
      Principle energy level (n) remains the same throughout the period
      Each successive element the atomic # Increase
      Add proton and electron
      Electron gets added to same Prin. E level (n)
      No additional electrons come across valence electrons and nucleus
      Val. E- are not shielded from increased nuclear charge
      Therefore the increased nuclear charge brings the outermost electrons closer to the nucleus …which means…
      Smaller atomic radii going   
    • Atomic Radius: Trends within Groups
      INCREASE as you move down a group
      Nuclear charge increases
      What happens to your principle energy level as you move down a group?
      Therefore…Electrons added to higher principle energy levels
      Although nuclear charge increased, other factors in play to overpower increased nuclear charge...
      Outermost orbital increases in size
      Electrons are farther from the nucleus b/c of bigger orbital
      More resistant to higher nuclear charge b/c of increased distance
      Principle energy level increased
      Puts more orbital with electrons between the nucleus and the outermost electrons
      These electrons in between shield the outermost electrons from the pull of the nucleus
    • Solve…
      Which has the largest radius?
      Magnesium (Mg)
      Silicon (Si)
      Sulfur (S)
      Sodium (Na)
      Which has the smallest radius?
    • And the answer is…
      Largest: Na (sodium)
      Smallest: S (sulfur)
    • Ionic Radius
      Losing/gaining electrons affects size of an atom
      Gain an electron atom becomes negative atom becomes larger
      Electrostatic repulsion between atom’s outer electrons increase
      Forces outer electrons to move further apart
      Makes radius bigger
      Lose an electron atom becomes positive atom becomes smaller
      Electron lost is valence electron
      Can lead to completely empty orbital=smaller radius
      Electrostatic repulsion between atoms decrease so they can be pulled closer to nucleus
    • Ionic Radius: Trends in Period
      What type of ions do you think will be formed on the left side of the table?
      Smaller positive ions
      What type of ions do you think will be formed on the right side of the table?
      Larger negative ions
      General Rule:
      Left-to-right across a period, the size of positive ions gradually decreases
      Around 5A and 6A, the size of much larger negative ions gradually decreases
    • Ionic Radius: Trends in Group
      What happens to the principle energy level as we move down a group?
      Increases
      Ion’s outer electrons are in a higher principle level
      This means an increase in ionic size
      Ionic radii increases as we move down a group for both positive and negative ions