Periodic Table

  • Henry Mosely created the periodic table we use today, organizing it by atomic number. He found out the number of protons is equal to the atomic number.

  • Element:

    • Pure substances that cannot be broken down into simpler substances

    • 90 are naturally occurring, 25 synthesized and made by scientists

  • Periods: Horizontal Rows on the Periodic Table

    • There are 7 periods

    • Each element in a period has the same number of energy levels

  • Groups/Families: Columns in the Periodic Table

    • 18 groups, numbered left to right

    • Have similar chemical and physical properties because they all have same number of valence electrons

  • Metals:

    • Chemical Properties

      • Few electrons in the valence shell

      • Easily lose electrons

      • Have positive charges and make cations

    • Physical Properties

      • Ductile, can be drawn into wires

      • Malleable, can be shaped pretty easily

      • Good conductors

      • Shiny

      • Solid at room temperature, besides He (Mercury)

  • Nonmetals

    • Chemical Properties

      • Almost full valence shell

      • Tend to gain electrons

      • Negative Charge

      • Makes anions

    • Physical Properties

      • Not ductile or malleable

      • Poor conductors

      • Mostly solid, but some are gaseous at room temperature

    • Metalloids/Semi-metals

      • Chemical Properties

        • Most have half full valence shells

        • Make anions or cations depending on environment

      • Physical Properties

        • Have properties of metals and nonmetals

          • Hard to know properties of each one

  • Shielding Effect: Inner shell electrons repel outer valence electrons, keeping the valence from feeling the full attractive force of the nucleus.

  • Effective Nuclear Charge (Zeff)

    • Is the relative attraction the valence electrons have for the protons in the nucleus.

      • Adding protons have greater effect than adding electrons

    • Zeff = Z - S

      • Z = Nuclear attraction (number of protons)

      • S = Inner electrons shielding the valence electrons. Is the total number of electrons minus the electrons in the highest occupied s and p energy levels.

  • Atomic radius is half the distance between two bonded nuclei and cannot be measured because orbitals are not tangible.

    • Increases when going down because of increased shielding, meaning:

      • More energy levels

      • Valence electrons further from nucleus

      • Increased shielding

      • Less attraction increases radius

    • Decreases when going right because more protons and increased nuclear charge, meaning:

      • More protons

      • Shielding does not increase because energy levels is constant

      • Stronger nuclear attraction so radius is smaller

  • Ionic Radius

    • Cations

      • Lose electrons

      • Always smaller than their neutral atoms

      • Reduced electron repulsion

      • Nucleus pulls on less electrons

      • Energy level might drop

    • Anion

      • Gain electrons

      • Larger than their neutral atoms

      • Extra valence electrons

        • more repulsions make it bigger

  • Isoelectric species: atoms/ions with the same number of electrons. Ex: O2- , F- , Ne

  • Ionization Energy

    • Energy required to remove an electron from a neutral atom

    • Noble gases have the highest ionization energy

    • Decreases down because further energy levels and increased shielding

    • Increases to the right because closer to full valence shell, increased effective nuclear charge pulls harder on valence electrons

    • Subsequent ionizations create a huge leap in ionization energy

  • Electronegativity

    • Electron affinity has same pattern as electronegativity

    • Measure of an atom in a chemical compound to attract electrons from another atom

    • Noble gases lowest because they do not care about attracting electrons

    • Decreases going down periodic table because electrons further away, increased shielding reduces nucleus pull on valence electrons as well as electrons from other atoms.

    • Increases to the right because of smaller radius, increased nuclear charge means nucleus is pulling harder on valence electrons where the bonds are occurring.

  • Reactivity

    • Metals and nonmetals have opposite trends, metals reactivity increases going down the periodic table while nonmetals more reactive going up the periodic table

      • Metals want to get rid of electrons and that is more effective when larger radius

      • Non-metals want to be highly electronegative to

    • Noble gases are inert and non-reactive