Unit 2 – Electrons and Periodic Behavior Cartoon courtesy of NearingZero.net

Period The Periodic Table Group or Family Group or family Period

Periodic Table Periodic table is divided into 3 classes Metals Non metals Metalloids The horizontal rows are called periods while the vertical columns of the periodic table are called Groups or Families

Properties of Metals Metals are good conductors of heat and electricity Metals are malleable Metals are ductile Metals have high tensile strength Metals have luster

Examples of Metals Potassium, K reacts with water and must be stored in kerosene Copper, Cu, is a relatively soft metal, and a very good electrical conductor. Zinc, Zn, is more stable than potassium Mercury, Hg, is the only metal that exists as a liquid at room temperature

Properties of Nonmetals Carbon, the graphite in “pencil lead” is a great example of a nonmetallic element. Nonmetals are poor conductors of heat and electricity Nonmetals tend to be brittle Many nonmetals are gases at room temperature

Examples of Nonmetals Microspheres of phosphorus, P, a reactive nonmetal Sulfur, S, was once known as “brimstone” Graphite is not the only pure form of carbon, C. Diamond is also carbon; the color comes from impurities caught within the crystal structure

Properties of Metalloids Metalloids straddle the border between metals and nonmetals on the periodic table. They have properties of both metals and nonmetals. Metalloids are more brittle than metals, less brittle than most nonmetallic solids Metalloids are semiconductors of electricity Some metalloids possess metallic luster

Silicon, Si – A Metalloid Silicon has metallic luster Silicon is brittle like a nonmetal Silicon is a semiconductor of electricity Other metalloids include: Boron, B Germanium, Ge Arsenic, As Antimony, Sb Tellurium, Te

The Properties of a Group: the Alkali Metals   Easily lose valence electron (Reducing agents)   React violently with water   Large hydration energy   React with halogens to form salts (valence electrons are electrons in the outermost shell of an atom)

Properties of Alkaline earth metals They are the group II A elements Denser, harder and stronger than Group I A elements but less reactive Too reactive to be found pure in nature

Halogens and Noble Gases Halogens are the most reactive of the non metals. They are the group VII A elements The noble gases are the group VIII A elements. They are also called inert gases because they undergo very few reactions.

Periodic Law When elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties.

The Bohr Model of the Atom I pictured electrons orbiting the nucleus much like planets orbiting the sun. But I was wrong! They’re more like bees around a hive. WRONG!!! Neils Bohr

Electron Energy Level (Shell) Generally symbolized by n, it denotes the probable distance of the electron from the nucleus. Number of electrons that can fit in a shell: 2n2

An orbital is a region within an energy level where there is a probability of finding an electron. This is a probability diagram for the s orbital in the first energy level… Orbital shapes are defined as the surface that contains 90% of the total electron probability.

Energy Levels, Sublevels, Electrons Sublevels in main energy level (n sublevels) Number of orbitals per sublevel Electrons per sublevel electrons per level (2n2) 1 s 2 p 3 6 8 d 5 10 18 4 f 7 14 32

Orbital filling table

Irregular conformations of Cr and Cu Chromium steals a 4s electron to half fill its 3d sublevel Copper steals a 4s electron to FILL its 3d sublevel

Periodic Trends How do properties of elements change as you go across a periodic table?

Half of the distance between nuclei in Determination of Atomic Radius: Half of the distance between nuclei in covalently bonded diatomic molecule "covalent atomic radii" Periodic Trends in Atomic Radius   Radius decreases across a period Increased effective nuclear charge due to decreased shielding   Radius increases down a group Addition of principal quantum levels

Table of Atomic Radii

ION An atom or a group of atoms that has a positive or negative charge are called ions. Atoms get a positive charge when they lose electrons Atoms get a negative charge when they gain electrons Ionization is the process that results in the formation of an ion.

Increases for successive electrons taken from the same atom Ionization Energy - the energy required to remove an electron from an atom   Increases for successive electrons taken from the same atom   Tends to increase across a period Electrons in the same quantum level do not shield as effectively as electrons in inner levels     Irregularities at half filled and filled sublevels due to extra repulsion of electrons paired in orbitals, making them easier to remove   Tends to decrease down a group Outer electrons are farther from the nucleus

Table of 1st Ionization Energies

Electronegativity A measure of the ability of an atom in a chemical compound to attract electrons   Electronegativities tend to increase across a period   Electronegativities tend to decrease down a group or remain the same

Periodic Table of Electronegativities

Summation of Periodic Trends

Ionic Radii Cations Anions Positively charged ions formed when an atom of a metal loses one or more electrons Cations   Smaller than the corresponding atom Negatively charged ions formed when nonmetallic atoms gain one or more electrons Anions Larger than the corresponding atom