Elements, Compounds & Mixtures

How everything is put together.

Classification of Matter

Elements

Matter that has the same composition and properties throughout is called an element.

• When different elements combine, other substances are formed.

Elements

Contains only one particle

Can exist in 3 states of matter solid, liquid, and gas

Picture from http://www.ilpi.com/msds/ref/gifs/statesofmatter.gif

Compounds Ban DHMO? DHMO is dihydrogen monoxide. Evaluate the following link and decide

if this potentially dangerous chemical should be prohibited.

www.dhmo.org

Compounds A compound is a substance

whose smallest unit is made up of atoms of more than one element bonded together.

• Compounds often have properties that are different from the elements that make them up.

• Examples: Water, salt, sugar

CompoundsGeneral Rules:

- Only write the name of the metallic element first

- Write the number of atoms of any element in the compound in subscript (applies to only 2 or more atoms)

- “ide” will always be written at the end of the non metal element

Compound Properties

Compounds are formed by atoms of different elements. However, they do not have the properties as them.

Because of chemical bonds, compounds cannot be broken down by physical means. They can only be broken down by chemical reaction or electricity.

How do we name compounds? Rule 1

A compound made up of two elements has a name that ends in -ide.

• Sodium chloride — made up of the elements sodium and chlorine • Zinc oxide — made up of the elements zinc and oxygen • Carbon dioxide — made up of the elements carbon and oxygen

Fixed Composition of Compounds

For example, water (H2O) is a compound made

only by joining together two atoms of hydrogen

to one atom of oxygen.

That is, the ratio of hydrogen atoms to oxygen

atoms in water is always 2 : 1.

A compound is made up of different elements

chemically combined in a fixed ratio.

Chemical Formula of a CompoundA compound can be represented by a chemical formula.

The chemical formula states • the types of atoms (i.e. elements) in the compound, • the ratio of the different atoms in the compound.

Types of atoms: hydrogen, oxygen

Ratio of H to O = 2:1

How do we write chemical formula?Rule 1

For many compounds that contain both metallic and non-metallic elements, the symbol of the metallic element is written first.

• calcium oxide (CaO) • sodium chloride (NaCl) • magnesium carbonate (MgCO3)

How do we write chemical formula?Rule 2

The number of atoms is written as a subscript, to the right of the atom’s symbol.

• water (H2O, not H2O or 2HO)

• magnesium carbonate (MgCO3, not MgCO3 or MgC3O)

How do we write chemical formula?Rule 3

It is not necessary to write the subscript ‘1’.

• water (H2O, not H2O1) • calcium oxide (CaO, not Ca1O1)

How do we write chemical formula?Rule 4

The oxygen atom is usually written at the end of the formula.

• water (H2O, not OH2) • carbon dioxide (CO2, not O2C) • nitric acid (HNO3, not O3NH)

Let’s try it… How many atoms of each element are there in the compound? Sulfuric Acid H2SO4

__ Hydrogen __ Sulfur __ Oxygen

Hydrogen Peroxide H2O2

__ Hydrogen __ Oxygen

And some more formulas… Carbon Dioxide COCarbon Dioxide CO22

__ Carbon __ Oxygen

Carbon Monoxide COCarbon Monoxide CO __ Carbon __ Oxygen

Calcium Carbonate CaCOCalcium Carbonate CaCO33

__ Calcium __ Carbon __ Oxygen

Compound Review  A pure compound has the same elements

and the same amount of elements all of the time

Elements are chemically combined

Compound properties are different from the properties of the elements

They cannot be separated physically

Physical properties such as boiling point or melting point of pure substances are do not change

Mixtures

A mixture is a combination of two or more substances where there is no chemical combination or reaction.

Mixtures combine physically in no specific proportions. They just mix.

Solids, liquids and gases can be combined to

create a mixture.

Mixture Types

MIXTURES MAY BE HOMOGENEOUS OR HETEROGENEOUS

Homogeneous Mixtures

Homogeneous Mixtures:

The prefix: "homo"- indicates the same

Have the same uniform appearance and composition throughout

Solutions

SOLUTIONS- are homogeneous

mixtures

What is a solution? A solution is a

mixture of two or more substances.

At least two substances must be mixed in order to have a solution

A solution has two parts The

substance in the smallest amount and the one that DISSOLVES is called the SOLUTE

The substance in the larger amount is called the SOLVENT - it does the dissolving

IN most common instances water is the solvent

                        

Examples of solutions

Salt water Clean Air Vinegar

Heterogeneous Mixtures:

The prefix: "hetero"- indicates difference

A heterogeneous mixture consists of visibly different substances or phases

Two or more parts can be seen

Examples:

Pizza Sandwich Chex Mix

Suspensions A SUSPENSION is a

heterogeneous mixture of large particles

These particles are visible and will settle out on standing

Examples of suspensions are: fine sand or silt in water or Italian salad dressing

Classification of Matter

Compounds vs Mixtures

CompoundsCompounds MixturesMixtures

•Combine chemically

forming molecules

•Not chemically Not chemically combinedcombined

•Combine in set proportions

•Can combine Can combine in any in any

proportionproportion

•Separated chemically

•Separated Separated physicallyphysically