TOPIC ONE

There are only certain regions in the electron cloud where electrons are likely to be found. These regions are called energy levels. The lowest energy level is closest to the nucleus; the highest energy level is farthest away from the nucleus. Electrons will occupy the lowest available energy level(s) before they fill in higher levels.

The outermost electrons in an atom are called valence electrons. The period (row) number on the periodic table corresponds to the highest energy level occupied by the valence electrons in an element.

Elements in the same group (column) on the periodic table have the same number of valence electrons. All of the group 1 elements have one valence electron and group two elements have two. Group 13 elements have three valence electrons, group 14 elements have 4, group 15 have 5 and so on through group 18 elements, which have eight valence electrons.

An ion is an atom that has a charge because it has gained or lost electrons. Positive ions (cations) have lost electrons; negative ions (anions) have gained electrons. The amount of charge is equal to the number of electrons lost or gained.

TOPIC TWO

Elements in groups 1, 2 and 13 (metals) will lose electrons and form positive ions (cations).

Elements in groups 15, 16 and 17 (nonmetals) will gain electrons and form negative ions (anions).

Ionic compounds are formed by the attraction between positive and negative ions. The charges must be balanced, resulting in a compound with no net charge.

When naming ionic compounds formed between group 1& 2 metals and group 15-17 nonmetals, the metal is written first followed by the nonmetal with its ending changed to “ide”  (Ex: MgO, magnesium oxide.)

TOPIC THREE

Phase changes (changes in physical state) occur at constant temperature. For example, water both freezes and melts at 0^oC (273K) and both boils and condenses at 100^oC (373K). Which phase change takes place depends on whether the molecules are speeding up (adding heat) or slowing down (cooling).

Delta H (ΔH) is a change in heat (or enthalpy).

Endothermic phase changes require heat (melting and boiling). ΔH is positive for an endothermic change.

Exothermic phase changes give off heat (freezing and condensing). ΔH is negative for an exothermic change.

The amount of heat needed to melt a specific amount of a solid is called the heat of fusion (ΔH_f).

The amount of heat needed to boil a specific amount of a liquid is called the heat of vaporization (ΔH_v).

Heating and cooling curves show phase changes. The flat part of the curve is when a substance is undergoing a phase change. Freezing and melting occur at the lower plateau temperature, while condensing and boiling occur at the higher plateau temperature. The length of the plateau on a heating curve indicates the relative amount of energy needed for the phase change.

TOPIC FOUR

The molar mass of a compound is the sum of the molar masses of the individual elements in the compound.

**TOPIC FOUR CONTINUED ON NEXT PAGE**

The percent by mass of an element in a compound can be determined:

                                     % by mass of element = total mass of element in compound  X 100

                                                                              total mass of the compound

TOPIC FIVE

A chemical equation is a record of what happens in a chemical reaction. It shows the formulas of all the reactants on the left hand side of the arrow, and the formulas for all the products on the right hand side.

A balanced chemical equation has the same number of atoms of each element on either side of the arrow.  When balanced, the coefficients show the number of moles (mole ratio) of each substance that are required for a complete reaction.

Solid (s), liquid (l), gas (g) and aqueous (aq) are the possible states of matter for a substance in a reaction.

TOPIC SIX

Solubility is defined as the amount of solute that will dissolve in 100 g of solvent.

Dissolving is a physical change that involves a change in heat.       Example: C₆H₁₂O_6(s) à C₆H₁₂O_6(aq)  + heat

Dissociation occurs when ionic substances dissolve. Dissociation can be represented by an equation.

                                             Example: NaCl(s)  ® Na⁺(aq) + Cl^-(aq)  

Note: A compound is breaking up into ions (the elements on the right have charges)! The formation of aqueous ions is how to recognize a dissociation equation.

If a solution gets colder when a solute dissolves, it is an endothermic change and ΔH is positive, and heat is written to the left of the arrow.   NaCl(s) + heat ® Na⁺(aq) + Cl^-(aq)    ΔH is positive

If a solution gets warmer when a solute dissolves, it is an exothermic change and ΔH is negative, and heat is written to the right of the arrow.     CaCl₂(s)  ® Ca²⁺(aq) + 2Cl^-(aq) + heat      ΔH is negative

TOPIC SEVEN

Determine the mean (average) of a set of volume (mL) or mass (g) measurements using the rules for significant digits.

A research question asks about the relationship being investigated.  A hypothesis predicts the answer to a research question based on prior observation. An explanation of a hypothesis justifies the prediction using quantified observations and theoretical background.