Unit 3 EMR, Orbitals, and Periodic Trends

Electromagnetic Radiation  EMR- energy being transmitted from one place to another by light

Light as a Wave  Scientists discovered early on that light travels through space exhibiting wave-like behavior  Wavelength (λ)– the distance between two consecutive wave peaks  Frequency (v) – how many wave peaks pass a certain point per given period of time  Shorter waves have a higher amount of energy, Longer waves have a lower amount of energy

Light as a Particle  Scientists later found that light also exhibited particle-like behavior.  Light travels through space as photons.  Photons – tiny packets of energy  Dual nature of light -Scientists have concluded that light behaves as both a wave and a particle.

EMR Calculations  The following formula is used to calculate the frequency or wavelength of a wave: c = λ v c = speed of light, always 3x10 8 m/s λ= wavelength, units: m v = frequency, Units Hz (1/s)

EMR Calculations  The following formula is used to calculate the energy of a wave: E = h v E = energy, units: Joules (J) h = Planck’s constant, always 6.626x m 2 kg/s v = frequency, Units Hz (1/s)

Examples  What is the frequency of a wave with a wavelength of 789 nanometers?

Example  How much energy does a wave with a frequency of 8.23 x Hz have?

Example  What is the wavelength of a wave that has an energy of 9.89 x J

Periodic Trends  We have seen many periodic trends so far during our studies in chemistry including reactivity amongst groups, valence electrons, and ion charges when atoms have gained/lost electrons  We are about to examine more periodic trends that have been found in chemistry including reactivity among metals/non- metals, electronegativity, ionization energy, and atomic radius.

Reactivity - Metals  Scientists have found through experiments that reactivity among the metals on the periodic table increases as you go right to left in the periods and top to bottom in the groups of the periodic table.  The increase from right to left is due to the lower amount of valence electrons which make it easier to attain noble gas electron configuration.  The increase from top to bottom is because the valence electrons of elements towards the bottom are farther away from the nucleus so there is less attractive force keeping them near the atom.

Reactivity - Nonmetals  Scientists have found through experiments that reactivity among the nonmetals on the periodic table increases as you go left to right in the periods and bottom to top in the groups of the periodic table.  The increase from left to right is due to the increase in valence electrons which causes the atom to pull in electons stronger to achieve noble gas configuration.  The increase from bottom to top is due to the valence electrons being closer to the nucleus and therefore a stronger attractive force would pull other electrons to the atom.

Electronegativity  Electronegativity is how strongly an atom pulls electrons to itself when it is bonded to other atoms.  Electronegativity increases from left to right and bottom to top on the periodic table. Why?  Fluorine is the most electronegative element. Why is Helium not the most electronegative?

Ionization Energy  Ionization Energy is the amount of energy needed to take an electron away from an atom  Ionization Energy increases from left to right and bottom to top on the periodic table. Why?  Helium has the Highest Ionization Energy

Atomic Radius/Atomic Size  Atomic Radius/Atomic size is simply how large an atom is compared to other atoms  Atomic Radius increases as you go right to left and top to bottom on the periodic table. Why?  Francium has the largest atomic radius

Summary  Reactivity: Metals increasesand  Reactivity: Nonmetals increasesand  Electronegativity and ionization energy increaseand  Atomic Radius/Atomic Size increases and

Summary  Remember that Noble Gases do not count when looking at the following periodic trends: Reactivity and Electronegativity. This is because they are stable and unreactive.

Practice  Rank the following elements from lowest to highest reactivity based on the periodic trend for reactivity:  Ca, Zn, Cr  K, Rb, Na  Br, I, Cl  F, C, N

Practice  Rank the following elements from lowest to highest electronegativity based on the periodic trend:  As, Sn, S  Mo, N, Ba

Practice  Rank the following elements from lowest to highest ionization energy based on periodic trends:  Hg, Ta, Os  Ag, Au, Cu

Practice  Rank the following elements from lowest to highest atomic radius/atomic size based on the periodic trends.  Al, B, Na  K, H, Cs