I will know how to classify substances as elements compounds, or mixtures.

I will be able to identify elements, compounds, and mixtures based on their properties.

Today’s Objectives

A pure substance is matter that always has exactly the same fixed and uniform composition.

• Table salt and Helium are two examples of pure substances.

• Substances can be classified into two categories—elements and compounds.

• Table Salt is a compound• Helium is an element

Pure Substances

An element has a fixed composition because it contains only one type of atom.

No two elements are the same. ◦ Hydrogen and Iodine are 2 completely

different substances.◦ In the following weeks we will discuss those

differences more.

Elements

Symbols for ElementsChemists use symbols of one or two letters to represent elements. The first letter is always capitalized. If there is a second letter, it is not capitalized.

• C represents carbon.• Al represents aluminum.• Au represents gold. (The Latin name

for gold is aurum.)

Elements

Symbols for Elements

Co represents CobaltCO would be 2 atoms, 1 Carbon atom & 1 Oxygen atom

Elements

Symbols for Elements

What about those Elements at the bottom with 3 letters?

Due to disputes over the discovery of some of the heavier elements, the International Union for Pure and Applied Chemistry (IUPAC) has devised a systematic naming scheme, based on Greek and Latin roots. When a new element is discovered, it is named by the following procedure:

Elements

Aluminum, carbon, and gold are elements that you can see in common objects, such as cans, pencils, and rings. Mixtures containing iodine are used to prevent and treat infections.

Elements

Aluminum Carbon Gold Iodine

Into what groups do we classify the elements by properties?

Classifying Elements

Into what groups do we classify the elements by properties?

Metals, Metalloids

& Nonmetals

Classifying Elements

MetalsThe majority of the elements on the periodic table are classified as metals. Metals are elements that are good conductors of electric current and heat.

• Except for mercury, metals are solids at room temperature.

• Most metals are malleable. • Many metals are ductile; that is, they can

be drawn into thin wires.

Classes of Elements

Metals

MetalloidsMetalloid elements are located on the periodic table between metals and nonmetals.

• Metalloids are elements with properties that fall between those of metals and nonmetals.

• For example, a metalloid’s ability to conduct electric current varies with temperature. Silicon (Si) and germanium (Ge) are good insulators at low temperatures and good conductors at high temperatures.

Classes of Elements

Metalloids

NonmetalsNonmetals generally have properties opposite to those of metals.

• Nonmetals are elements that are poor conductors of heat and electric current.

• Nonmetals have low boiling points–many nonmetals are gases at room temperature.

• Nonmetals that are solids at room temperature tend to be brittle. If they are hit with a hammer, they shatter or crumble.

Classes of Elements

Nonmetals

Periodic Table of Elements

METALS METALLOIDS NONMETALS

SHINY

DULL

MALLABLE

DUCTILE

BRITTLE

ElectricalConductor

Thermal Conductor

A compound always contains two or more elements joined in a fixed proportion.

Compounds

A compound is a substance that is made from two or more simpler substances and can be broken down into those simpler substances.

The properties of a compound differ from those of the substances from which it is made.

• Water is composed of the elements hydrogen and oxygen. Oxygen and hydrogen are gases at room temperature, but water is a liquid.

• Hydrogen can fuel a fire, and oxygen can keep a fire burning, but water does not burn or help other substances to burn.

Compounds

The properties of a compound differ from those of the substances from which it is made.

• Table Salt, Sodium Chloride (NaCl), is comprised of the elements Sodium (Na) and Chlorine (Cl). At room temperature, Sodium is a solid and Chlorine is a gas produce Table salt a solid.

• Sodium is silvery-white and when expose to water will burn. Chlorine is a greenish-yellow gas that is used to treat drinking water. NaCl is required to sustain life.

Compounds

How do mixtures differ from pure substances?

Mixtures

If you make salsa, a recipe can guide you. You can use exactly the amounts in the recipe, or you can adjust the ingredients to your own taste. Salsa is a mixture. Each batch may be slightly different.

Mixtures

The properties of a mixture can vary because the composition of a mixture is not fixed.• Mixtures can retain some of the properties of their individual substances.

• The properties of a mixture are less constant than the properties of a substance.

Mixtures

Mixtures can be classified by how well the parts of the mixture are distributed throughout the mixture.

Heterogeneous Mixtures In a heterogeneous mixture, the parts of the mixture are noticeably different from one another.

Homogeneous Mixtures In a homogeneous mixture, the substances are so evenly distributed that it is difficult to distinguish one substance in the mixture from another. (similar)

Mixtures

The sand is a heterogeneous mixture of different kinds of grains. The spoon is stainless steel, a homogeneous mixture of iron, chromium, and nickel.

Mixtures

Classifying MixturesHomogeneous Heterogeneous

With your group, identify each substance as an element, mixture, or compound.

EMC Identification Lab

On the back of your data table, list three elements, three compounds, and three mixtures not discussed in class.

On Your Own

Compare and contrast the properties of compounds with the properties of the elements that make up the compounds.

Wrap Up