Periodic Table: Patterns

A Few People Dobereiner- organized elements into “triads” Triad – set of 3 elements with similar properties

Newlands Noticed patterns of eight or octaves Arranged elements based on weight

Lothar Meyer Organized elements in a useful way but does not get as much credit as

Mendeleev Organized elements based on atomic weight - no idea of atomic number or number of protons at this time ~1868

Mendeleev’s Table Left “blank spaces” for elements that had not yet been discovered He predicted the chemical and physical properties of elements that had yet to be discovered (quite accurately)

Mosely 1913 - arranged the periodic table by the number of protons (atomic number) We use this version today

Periodic Law Elements are arranged by increasing atomic number ; there is a periodic repetition in their physical and chemical properties. Mendeleev and Mosely understood this Periodic Law

Periodic Law It did not work for 100 % of the elements

Periodic Table Horizontal rows: Vertical columns: Called Periods Show the number of the shell or Energy level Vertical columns: Called groups or Families Show the valence electrons Elements in a group have similar physical and chemical properties

Group A Vs. Group B Group A known as the Representative Elements Includes 1A- 8A Group B known as the Transition Elements Includes elements3B, 4B, 5B, 6B, 7B, 8B, 1B , 2B

Valence Electrons Do you remember how to determine the number of valence electrons? Transition and Inner Transition metals generally have 2 or 1 valence electrons

Classification of Elements Another way to classify (Metals, Nonmetals and Metalloids)

Metals, Nonmetals, and Metalloids There is a zig-zag or staircase line that divides the table. Metals are on the left of the line, in blue. Nonmetals are on the right of the line, in orange.

Metals, Nonmetals,and Metalloids Elements that border the stair case, shown in purple are the metalloids or semi-metals.

Metals Metals lustrous malleable ductile good conductors of heat and electricity Form + ions They are mostly solids at room temp. What is one exception?

Nonmetals Nonmetals Dull Brittle Nonconductors (insulators) Some are solid, but many are gases, and Bromine is a liquid. Form - ions

Metalloids Metalloids (semi-metals) characteristics of both metals and nonmetals shiny but brittle semiconductors

Periodic Trends There are several important atomic characteristics that show predictable trends that you should know. The first and most important is atomic radius. Radius is the distance from the center of the nucleus to the “edge” of the electron cloud.

Atomic Radius Distance from the Nucleus of one atom to the nucleus of the other atom Two Br atoms bonded together are 2.86 angstroms apart. So, the radius of each atom is 1.43 Å. 2.86 Å 1.43 Å

Element Characteristics Atomic radius Radius size increases Radius size decreases

Atomic Radius Vertical Column – size increases With each step down the family, we add an entirely new energy level to the electron cloud, making the atoms larger with each step. Horizontal Row- size decreases (generally) Each step adds a proton and an electron (and 1 or 2 neutrons). Electrons are added to existing sublevels. (They are not getting bigger)

Effective Nuclear Charge The effect is that the more positive nucleus has a greater pull on the electron cloud. The nucleus is more positive and the electron cloud is more negative. The increased attraction pulls the cloud in, making atoms smaller as we move from left to right across a period.

Ionization energy generally decreases Energy required to overcome the attraction of the nuclear charge and remove an electron from an atom to form an ion Easier to remove an electron from group 1 than group 8 Easier to remove electrons that are farther away from the nucleus (elements at the bottom of a group) Ionization energy generally decreases Ionization energy increases

Electronegativity decreases It is the ability for atoms of an element to attract electrons when they are chemically combined with another element Electronegativity decreases Electronegativity increases

Element Characteristics More nonmetallic Liquids Periodic Table More metallic Solids

Periodic Table Trends: Summary Atomic radius decreases Ionization energy and Electronegativity increase