52
Elements, Compounds & Mixtures How everything is put together.
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, it is the universal solvent.
Examples of solutions
Salt water Clean Air Vinegar
List 3 solutions and name the solute and solvent.
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
List 4 examples of your own
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
What is it?
Trail Mix
Heterogeneous
What is it?
Kool - Aid
Homogeneous
What is it?
Water
Homogeneous
What is it?
White Vinegar
Homogeneous
What is it?
Italian Salad Dressing
Heterogeneous
Try these………..
Raisin Bran
Orange Juice
Air
Chunky Soup
Hamburger
Cake Batter
Paint
Salad
Mineral Rock
Answers: Raisin Bran – heterogeneous Orange Juice – homogeneous Air – heterogeneous Chunky Soup – heterogeneous Hamburger – heterogeneous Cake Batter – homogeneous Paint – homogeneous Salad – heterogeneous Mineral Rock - heterogeneous
