1 - 1 Substances A pure substance is an element or a compound. Substances have the same characteristics throughout meaning that all samples have the same characteristics. An element is a substance composed of only one kind of atom. Elements can not be broken down into a simpler substance by ordinary chemical means.

1 - 2 Elements and Compounds Examples of elements:  oxygen, carbon, nitrogen Compounds are homogeneous substances formed by the chemical bonding of two or more different kinds of atoms resulting from a chemical reaction. Compounds have properties uniquely different from the elements making it up.

1 - 3 Compounds Examples of compounds:  water, carbon dioxide, sodium chloride The Law of Definite Proportions states the mass of the constituent elements always remains the same.  In every 100. g sample of NaCl, 39.3 g is sodium and 60.7 g of chlorine.

1 - 4 Compounds and Mixtures When a compound is formed, evidence of a chemical reaction is usually obvious.  Light is given off or heat is either absorbed or liberated. Mixtures are physical combinations of two or more substances.

1 - 5 Mixtures In a mixture, the components can be present in any proportion.  NaCl(aq) – a salt water solution can exist in any proportion. When a mixture is formed, there is no evidence of a chemical reaction taking place. In a mixture, the components do not lose their identity.

1 - 6 Mixtures Mixtures can be either homogeneous or heterogeneous.  Mixtures having uniform characteristics are homogeneous.  Mixtures having varying characteristics throughout the sample are heterogeneous.

1 - 7 Classification of Matter Matter Pure Substance Mixture Element Compound Homogeneous Heterogeneous Matter

1 - 8 Physical Properties Characteristics that can be observed without producing a new substance.Examples colordensity odormelting point volumeboiling point compressibilitymass

1 - 9 Chemical Properties Characteristics that describe how a substance reacts with another substance to form a new substance. 2H 2 (g) + O 2 (g) 2H 2 O(l) The reactants hydrogen and oxygen have much different characteristics than the product water.

Physical Changes No new substances are formed as a result of a physical change. In a physical change, one or more physical properties are changed. Changes of state or phase such as condensation or vaporization and changes in size by tearing, breaking, grinding are examples of physical changes.

Chemical Changes A chemical change results in the formation of one or more new substances. The new substances differ in chemical properties and composition from the original substance. Examples of Chemical Changes  rusting of iron  burning of paper

Chemical Changes When the following are not associated with a change of phase (state), they represent a chemical change.  formation of a gas (bubbles)  formation of a solid (precipitate)  absorbing (endothermic) or giving (exothermic) off heat

Properties Properties are characteristics that used to describe substances. Properties can be either extensive or intensive. Extensive properties depend on the amount of substance present.  Examples are weight, mass, volume, and length.

Properties Intensive properties are independent of the amount of substance present.  Examples are density, temperature, and boiling point.

Law of Definite Proportions Once a given compound is formed, its chemical composition is always constant. 2C(s) + O 2 (g) → 2CO(g) The mass ratio is:C:O12 g:16 g The atom ratio is:C:O 1 C:1 O

Law of Multiple Proportions Two elements combining with each other may join in varying ratios to form different compounds (compare to the product formed in previous slide). C(s) + O 2 (g) → CO 2 (g) The mass ratio is:C:O12 g:32 g The atom ratio is: C:O 1 C:2 O

Dalton’s Atomic Theory All matter is composed of atoms and an atom is the smallest particle of an element that takes part in a chemical reaction. All atoms of an element are alike. Compounds are combinations of atoms of one or more elements. The relative number of atoms for each element is always the same.

Dalton’s Atomic Theory Atoms can not be created or destroyed in a chemical reaction. Atoms can only change how they combine with each other.