Periodic Trends. Organization of the Periodic Table. GROUPS. Columns of the periodic table Atoms of elements in the same group have the same # of valence electrons and therefore behave similarly. PERIODS. Rows of the periodic table All elements in a period have
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GROUPS • Columns of the periodic table • Atoms of elements in the same group have the same # of valence electrons and therefore behave similarly PERIODS • Rows of the periodic table • All elements in a period have • their valence electrons in the same energy level.
Valence Electrons • Valence Electrons are electrons in the outermost energy level. • - s or p electrons only (even when d and f electrons are present they are not in the outermost energy level)
Electron Dot Diagrams • Electron Dot Diagrams show the valence electrons of an element. • Draw the electron dot diagrams for the following: • Mg N F
Size of the Atom • Think of a ball of an onion. What happens with each layer? • As you go down the periodic table, the energy levels increase and the size of the radius of the atom increases. (each energy level is like another layer of the onion)
Atomic Radius cont. • As you move from left to right in the periodic table, what happens to the number of protons in the nucleus? • What effect do these protons have on the electrons? • What effect do the electrons have on each other?
Electron Shielding • Electron Shielding (or Screening) – These inner electrons shield the valence electrons from receiving the entire attractive nuclear charge because they repel the valence electrons.
Nuclear Charge and Atomic Radius • Within a period, as you go from left to right, the positive nuclear charge increases, and attracts the electrons more strongly. • As the electrons are more attracted to the nucleus, the atomic radius decreases. • Summary: as you go from left to right, the atomic radius generally decreases.
Octet Rule • The octet rule states that all atoms attempt to become stable by having a full valence electron shell (generally 8 electrons, hence octet rule). • Atoms will gain, lose, or share electrons in order to attain this stability.
Which group is one electron away from a full octet? • Alkali metals • Transition metals • Halogens • Alkaline earth metals • Both alkali metals and halogens • Noble gases • Both alkali metals and alkaline earth metals
Ionization Energy • Electrons are held in atoms by their attraction to the positively charged nucleus. • To remove an electron requires energy. • Ionization energy is the energy required to remove the least tightly bound (or outermost) electron from an atom.
Ionization Energy cont. • Compare Li and K. • How many valence electrons? • What is the relative size of the atoms? • Which has a higher ionization energy?
Ionization Energy • As you go down a group, the ionization energy decreases because it takes less energy to remove an electron. • The least tightly bound electrons are further from the positive nucleus, and can therefore be removed more easily.
Second, Third, etc. Ionization Energy • Second ionization is the energy required to remove a second electron. • Ex. Sodium has a lower (first) ionization energy than Magnesium but Mg has a lower second ionization energy than Na. • Why?
Electronegativity • Electronegativityis the tendency of an element to attract electrons in a bond. • Therefore, elements that want to gain electrons will have higher electronegativity. attractive
