1. Mixtures, Compounds, and Elements

2. Introduction
We classify all types of things. Library books are classified according to the Dewey decimal system, department stores classify their clothing by size, and grocery stores classify their food according to the type of food.
We classify matter according to makeup.

3. Mixtures
Matter that consists of 2 or more substances mixed together but not chemically combined.
Examples: sand, granite, concrete, and salads

4. Four Properties of Mixtures
The key characteristic is that each kind of molecule in the mixture keeps its own identity.
A mixture of salt and pepper has particles of salt that keep salt properties and particles of pepper that keep pepper properties.

5. Four Properties of Mixtures
A second property is that substances in a mixture may change in physical appearance.
Some physical properties may change, but the substances do not change in chemical composition
Examples: boiling point may change, melting point may change

6. Four Properties of Mixtures
Substances that make up a mixture can be present in any amount.
In a breakfast cereal:
You put in cereal, milk, and fruit
However, you don’t always put in the same amount of each in your bowl.

7. Four Properties of Mixtures
Mixtures can be separated into their parts by using physical means.
We can use a filter to separate solids and liquids (coffee maker)
We can use a magnet to separate iron filings from sulfur
We can use a fork to separate the parts of a pizza

8. Types of Mixtures Mixtures are classified by how well mixed they are.
Heterogeneous mixtures are mixtures that do not appear to be the same throughout.
Examples are salt & pepper, cheeseburgers, sand & water, oil & vinegar

9. Types of Mixtures
Suspensions are mixtures in which the particles of one substance become scattered throughout another w/o dissolving. After a while the particles separate because of their large size.
Examples: solid/liquid-sand & water solid/gas-smoke, gas/liquid-shaving cream

10. Types of Mixtures
Homogeneous mixtures are mixtures that appear to be the same throughout. They are “well mixed”.
Colloids and solutions are homogeneous mixtures

11. Types of Mixtures
Colloids are homogeneous mixtures with particles smaller than suspensions (too small to be seen) but still relatively large. The particles are permanently suspended
Examples are milk-fat&water, blood-cells &water, fog-water&air
Colloids often appear cloudy

12. Types of Mixtures
Colloids are cloudy because the particles are large enough to scatter or bend light.
Emulsions are colloids of one liquid suspended in another.
An example is mayonnaise which is an emulsion of vinegar, oil and egg yolk. The egg is an emulsifier.

13. Types of Mixtures
Solutions are a special kind of homogeneous mixture. They are the “best mixed” of all mixtures.
In a solution one substance dissolves in another, and the particles spread out evenly.

14. Types of Mixtures
The particles cannot be seen because they have broken down into very small particles.
Examples of solutions are air, lemonade, tea, ocean water.

15. Properties of Solutions
If one substance dissolves in another it is said to be soluble. The substance that is being dissolved is the solute, and the substance that does the dissolving is the solvent. Water is the universal solvent.

16. Properties of Solutions
Most solutions cannot be separated by simple physical means. This is because of the very small size of the particles. We can separate solutions by more complex physical means such as distillation.

17. Properties of Solutions
Many solutions appear clear and solutions.
In a solution the particles are evenly spread out. A solution looks the same in the first drop as the last drop.

18. Describing Solutions A solution can contain varying amounts of solute.
A solution with a small amount of solute is dilute.
A solution with a large amount of solute is concentrated.

19. Describing Solutions
When no more solute can be dissolved at that temperature and pressure, the solution is saturated.
Usually as the temp increases, more solid solute can dissolve in a liquid solvent.
Usually as the temp increases, less gas solute can dissolve in a liquid solvent.

20. Determining Solubility
The amount of a solute that can dissolve in a given amount of a solvent at a specific temperature is called the solubility.
Graphs showing the amount of solute that will dissolve at a given temperature are called solubility curves.

21. Elements Pure substances are made of particles that are all alike.
The simplest pure substances are elements.
An element cannot be changed into simpler substances by heat, light, or electricity.

22. Elements Elements contain only one kind of atom.
An atom is the smallest particle of an element that has all the properties of that element.
Atoms of the same element are alike, the atoms of different element are different.

23. Chemical Symbols
Chemical symbols are a shorthand form of the elements name.
Symbols consist of one or two letters.
The first letter is always capitalized.
The second letter is never capitalized.

24. Chemical Symbols
Two letters are needed when the first letter of that element has already been used. C, Ca, Cu
We often use the Latin name of an element as its symbol. Au-aurum, Ag- argentum, Pb-plumbum.
Elements don’t have names yet.

25. Compounds Not all pure substances are elements.
Water and salt are not elements. They can be broken down.
Compounds are pure substances that are made of more than one element. The scientific definition is a substance formed by the chemical combination of elements.

26. Compounds
Compounds can be broken down into simpler substances (elements) by chemical means (heating, electrolysis).
The properties of compounds are quite different from the properties of the elements that make up the compound. Sodium-poisonous,chlorine-poisonous

27. Compounds Sodium chloride is not poisonous. Your body needs it.
When a particular compound forms, it always contains the same elements and the atoms of the elements are always in the same ratio. Water forms from 2 atoms of hydrogen and 1 atom of oxygen

28. Compounds
When two or more atoms are chemically joined a molecule is formed.
A molecule is the smallest part of a compound that has all the properties of that compound.

29. Chemical Formulas
We can think of chemical symbols as the letters of the alphabet.
Chemical symbols can be put together to form chemical “words”.
A combination of chemical symbols are called chemical formulas.

30. Chemical Formulas
Chemical formulas are a shorthand way of representing chemical substances.
A formula includes symbols of elements and numbers to show the ratios of atoms.
Usually formulas represent compounds. H2O

31. Chemical Formulas
Sometimes chemical formulas represent a molecule of an element. F2, Cl2, H2, O2.
Elements that occur in nature as two atoms bonded together are called diatomic molecules.

32. Chemical Formulas
Numbers written to the right of and below the symbol of an element are called subscripts. Subscripts tell the number of atoms of a particular element that are present in a compound. H2SO4
We never write a 0 or 1 as a subscript. If no subscript is written, it is understood to be 1.

33. Chemical Equations
If chem symbols are letter, and chem formulas are words, then we can write chemical sentences. Chem sentences are a way to describe a chemical process. During a chemical rex’n, substances are changed into new and different substances through the rearrangement of atoms.

34. Chemical Equations
A chemical equation describes a chemical reaction using symbols and formulas.
Hydrogen combines with oxygen to form water. H2 + O H2O

35. Chemical Equations
You must have the same number of atoms coming out of a reaction as you had going in-Law of Conservation of Matter.
To account for this we balance equations

36. Chemical Equations
Never touch a subscript. If you do you change the compound and that would not describe the reaction you have witnessed.
Add coefficients-whole numbers in front of a chemical formula.
2H2 + O H2O

37. Chemical Equations
To balance the number of atoms, multiply the coefficients times the subscript.
Remember the order of operations with parentheses. Multiply subscript inside X subscript outside X coefficient.