• What Is the World Made Of?

Examples:
Gold, water, oxygen, table salt

Distinguishing Substances and Mixtures

• If the composition of a material is fixed,

and if its constituents are chemcially combined, it is a substance;
 
• if the composition of a material can be variable,

and if its constituents are only physically combined, it is a mixture.

Substances can be either elements or compounds.

Distinguishing Elements and Compounds

• Elements are pure substances that cannot be broken down into simpler components through chemical processes; compounds are pure substances that can be broken down.

Atoms
The smallest unit of an element that maintains the chemical identity of the element

Each element is composed of only one kind of atom;
the atoms of different elements are all different.

Examples
The Five Most Common Elements in Living Things (& their Chemical Symbols)
 

carbon C

hydrogen H

oxygen O

nitrogen N

phosphorus P

Organic Compounds
Compounds containing carbon found in or produced by living things

Five Most Important Classes of Organic Biomolecules

Class	Common Name(s)	Examples
Carbohydrates	Sugars	glucose, sucrose, cellulose
Lipids	fats, oils, waxes, steroids	triglycerides, estrogen
Proteins	proteins & enzymes	Keratin, lactase
Nucleic Acids	genetic material	DNA & RNA

Example:
    sodium, a soft, silvery metal that reacts vigorously with water;

    chlorine, a poisonous yellow gas;

    When they are combined as ionic compound sodium chloride—also known as salt—
          the compound is a crystalline solid used to season food.

Symbols and Formulas

• Chemists use chemical symbols to represent elements and
• chemical formulas to represent compounds.

Examples:

Chemical Formula
A representation of a compound using chemical symbols to represent the elements present, with subscript numbers to represent their relative proportions

Example:
Water, H₂O —
2 hydrogen for every oxygen

oxygen gas, O₂ —
2 oxygen atoms bonded together

carbon dioxide, CO₂ —
2 oxygen for every carbon

glucose (blood sugar) C₆H₁₂O₆ —
a ring of six carbon atoms, with 2 hydrogens or a hydrogen and a hydroxyl group (-OH) attached to each of the carbons

Chemical Change
A change that produces matter with a different composition than the original matter by breaking down and recombining the constituents of other compounds

Examples:
Hydrogen gas and oxygen gas combine to form water:

2 H₂ (g) + O₂ (g) —> 2 H₂O (l)

The combustion of glucose in the presence of oxygen produces carbon dioxide and water:

C₆H₁₂O₆ (s) + 6 O₂ (g)—> 6 CO₂ (g) + 6 H₂O (l)

What is the world made of?
 

Practice Problems Answer the following questions:

1. What is a substance? a)  Give an example of a substance. . b)  Is salt water a substance?  Why or why not? .

2. What are compounds?

3. What are elements?

4. Distinguish between an element and a compound.

5. What are atoms?

6. What are the five most common elements in living things?

7. What are organic compounds?

8. What are the four most important classes of organic compounds?

9. What are the chemical symbols for the following elements? . a)  carbon b)  nitrogen c)  copper . d)  oxygen e)  lead f)  tin

10. What are the elements represented by the following chemical symbols? . a)  P b)  K c)  H . d)  Fe e)  Au f)  Sb . g)  Ar h)  Hg

11. What are the elements in the following substances and how many of each are there? a)  potassium phosphate, KH2PO4 . b)  the amino acid tryptophan, C11H12N2O2 . c)  the estrogen steroid hormone, estradiol, C18H24O2 .