ELECTRON CONFIGURATION REVIEW FROM UNIT 6 CHAPTER 18.3

Electron Configuration Electrons are organized on the outside of the atom in orbitals. An orbital is a region of space around the nucleus of an atom where an electron is likely to be located. They move like planets around the sun. Each electron in an atom has a specific amount of energy and the energy of an electron can change.

Energy Levels The possible energies an atom can have are called energy levels. An electron in an atom can move from one energy level to another when the atom gains or loses energy. Staircase analogy The level closest to the nucleus that has the least energy has the lowest number of electrons, 2.

Energy Levels An electron configuration is the arrangement of electrons in the orbital of an atom. The most stable electron configuration is the one in which the electrons are in orbits with the lowest possible energy.

Valence Energy Level A valence electron is an electron that is in the highest occupied energy level of an atom. These electrons play a key role in chemical reactions. Elements in a group have similar properties because they have the same number of valence electrons. (Hydrogen location on periodic table) When the highest occupied energy level is full an atom is stable. (HAPPY.)

BONDING AND DOT DIAGRAMS CHAPTER 19.1

Electron Dot Diagram An electron dot diagram is a model of an atom in which each dot represents a valence electron. The symbol in the center represents the nucleus of and all other electrons in an atom.

Stable Electron Configurations When the highest occupied energy level of an atom is filled with electrons, the atom is stable and not likely to react. Noble gases

Chemical Bond Elements that do not have a complete set of valence electrons tend to react with another element to achieve complete electron configurations. They do this by “bonding”. A process of sharing or giving/taking electrons. A chemical bond is the force that holds atoms together as a unit.

Octet Rule You have a complete set of valence electrons when you fulfill the Octet rule. The octet rule states that the element has eight valence electrons. In other words the valence is FULL! Sometimes this can only happen if two elements bond together.

Ionic Bonds An ionic bond is a type of bond created with electrons are transferred from one atom to another. Give and Take Usually metal to non-metal This process can create IONS. Bond is possible because opposite ions attract

Covalent Bond A covalent bond is a bond where two atoms share a pair of valence electrons Polar - has oppositely charged ends Non-polar – ends are charged the same Bond is possible b/c protons attract to shared electrons

CHEMICAL FORMULAS Notes 19.2 and 19.3

Chemical Formula The short-cut way of writing a compounds name. Chemical formula shows the symbol and the ratio of atoms by using subscripts. For Example:H2O

Oxidation Numbers An oxidation number indicates how many electrons are lost, gained or shared when bonding occurs. When writing the oxidation number the charge symbol is written after the number. For Example: 3+

Groups 3-12 Are special. They have many different oxidation numbers.

Writing Chemical Formulas for Ionic Compounds Use the name of the compound to identify the symbols of the elements. Using the periodic table, assign oxidation numbers to each element or group. Put the ions in the correct order. Cation first, Anion second. Criss Cross the oxidation numbers to identify how many atoms of each element are needed to make a neutral compound.

Ion An Ion is an atom that has a net positive or negative electric charge Anion – An ion with a negative charge Cation – An ion with a positive charge

Writing a Chemical Formula for Covalent Compounds Use the same procedure. Only change Metal is written first (least electronegative), Nonmetal is written second (more electronegative). Identify the type of covalent compound. Polar - has oppositely charged ends Non-polar – ends are charged the same

Transition Metals (Group 3-12) When writing a chemical formula that includes a transition metal, you must use a reference table. The oxidation number of the transition metal is represented in the name of the compound using roman numerals.

Polyatomic Ions Sometimes a group of ions act as one atom. They have only one charge for their group. You do not need to memorize these special ions, they will always be available for you in a reference table.

Polyatomic Ions

Writing a Chemical Formulas for Ionic Compounds with Polyatomic Ions! The same process applies as writing an ionic compound. Use the criss-cross method for ease. Keep the polyatomic ion together, using parenthesis if necessary.

Formula Mass The mass of one molecule of a compound relative to the mass of other compounds. Add up the mass of all the atoms in a chemical formula for a total mass.

HOW TO NAME A COMPOUND Notes 19.2

Naming Ionic Compounds Identify the formula of the compound. Identify which element is written 1st / 2nd. Write the full name of the first ion. Exception: Transition Metals Write the name for the second ion. Element- Change ending of element to –ide. Polyatomic Ion- Write full name.

CHEMICAL CHANGES Notes 20.1

Comparison of Physical and Chemical Properties

Physical Property Any characteristic of a material that can be observed or measured without change in the composition of the substances in the material. Properties include: Size Shape State Ex. Braiding Hair / Cutting Hair

Examples of Physical Properties

Using Physical Properties to Separate Mixtures Filtration: a process that separates materials based on the size of their particles. Distillation: A process that separates materials based on their boiling points.

Chemical Properties Can be observed only when the substances in a sample of matter are changing into different substances.

Is a Change Chemical or Physical? When matter undergoes a chemical change, the composition of the matter changes. When matter undergoes a physical change, the composition of the matter remains the same.

Changes… Physical Ice to Water to Steam Chemical Flammability, Reactivity Change in color Production of a gas Formation of a precipitate

CHEMICAL EQUATIONS Notes 20.2 and 20.3

Chemical Equations A short hand method of representing a chemical reaction. REACTANTS: The materials with which you start the reaction. PRODUCTS: The materials that are created by the reaction.

Symbols Symbol Meaning  Produces + Plus (cr) Crystalline solid (l) Liquid (g) Gas (s) solid

Conservation of Atoms The quantity of each type of atom you start a reaction with must be equal to the quantity and type of atoms you have when the reaction is over. Reactants = Products

Balancing Equations If this principle is not met in an equation, the equation must be balanced. You can add a coefficient to formula’s in the equation to help achieve conservation of atoms.

Coefficients Coefficients are numbers that represent the quantity of each substance taking part in the reaction. You only show a coefficient in an equation if the number is greater than 1.

Law of Conservation of Mass Not only do the quantity of atoms before and after a reaction have to be equal, but also the mass of the products must be equal to the mass of the reactants!

BALANCING EQUATIONS Notes 20.2

Examples on Overhead Projector…..