Unit 1A ACS Chemistry in the Community Sixth Edition

Unit 1A | ACS Chemistry in the Community, Sixth Edition | ©2012 BFW Publishers

Unit 1A

ACSChemistry in the CommunitySixth Edition


Chemical Symbols and Formulas

UNIT 1.A.5-6 AND 7


Mixtures, elements, compounds

Scientists like to classify things.

One way that scientists classify matter is by its composition.

Ultimately, all matter can be classified as mixtures, elements and compounds.


By asking these questions scientists can classify matter into:

Mixtures – two or more substances that are not chemically combined with each other and can be separated by physical means. The substances in a mixture retain their individual properties. Solutions – a special kind of mixture where one

substance dissolves in another. Elements – simplest form of pure substance.

They cannot be broken into anything else by physical or chemical means.

Compounds – pure substances that are the unions of two or more elements. They can be broken into simpler substances by chemical means.


Elements

Elements are the simplest pure substance. An element can not be changed into a simpler

substance by heating or any chemical process. The smallest particle of an element that

has the properties of that element is called an atom. An atom is the basic building block of matter.

There are more than one hundred known elements in the universe listed on the periodic table of elements. These elements combine in such a way to

create millions of compounds.


Elements

All elements are made of atoms.

Atoms of the same element are alike.

Atoms of different elements are different.


Elements

In 1813, a system of representing elements with symbols was introduced. Each symbol consists of

one or two letters. Two letters are needed for

a chemical symbol when the first letter of that element’s name has already been used.


Common Elements

Aluminum Al

Bromine Br

Calcium Ca

Carbon C

Gold Au

Helium He

Hydrogen H

Nitrogen N


Chemical Symbols

All elements in the Periodic Table have symbols that are recognized world wide.

It does not matter which country you are in or the language you speak.

Example: The element Iron is always identified by “Fe” and Oxygen is “O”.

The names are not always the same but the symbols are. “Fe” is iron in Canada, fer in France and fier in Romania.


Chemical Symbols

A Chemical symbol is an abbreviation of a name of an element.

Capital letter if only one letter.

Only first letter capital if more than one letter

Element Chemical Symbol

Oxygen O

Nitrogen N

Hydrogen H

Sodium Na


Sodium comes from the word sodanum, a headache remedy, and it’s symbol (Na) comes from the Latin word Natrium.



Compounds

Compounds are also pure substances.

But compounds are made from more than one element.

Water is a compound.

Water can be broken down into simpler substances – hydrogen and oxygen.



Chemical FormulasA chemical formula is the combination of

symbols that represent a particular compound.

The chemical formula indicates which elements are present in the compound and in what proportions.

Ex. 1: Water molecule

H2O: 2 atoms of hydrogen, 1 atom of oxygen

Ex. 2: Iron Oxide molecule

Fe2O3: 2 atoms of iron, 3 atom of oxygen


Chemical Formulas - Examples

Calcium Carbonate (chalk) – CaCO3

Sodium Chloride (salt) – NaCl Acetysalicylic acid (aspirin) –

C9H4O8

Acetic acid (vinegar) – C2H4O2


Chemical Formulas

NOTES:

- Each symbol in a formula represents an element.

- If only one atom of an element is present in the compound, no subscript is used.

- If more than one atom of an element is used, then the symbol is followed by a number indicating how many atoms are used. This is called the subscript.



I. CHEMICAL EQUATIONSA. Definitions 1. Chemical Equation - represents reactants and products in a reaction using symbols, formulas and coefficients. 2. Subscript - indicate the number of atoms of an element in a chemical reaction. 3. Coefficient - whole number in front of a formula or symbol that indicates the number of atoms, molecules, formula units or moles


Subscripts vs. Coefficients

The subscripts tell you how many atoms of a particular element are in a compound. The coefficient tells you about the quantity, or number, of molecules of the compound.



CHEMICAL REACTIONS

Reactants: Zn + I2 Product: Zn I2


Chemical Reactions

Chemical_Reactions.asf


B. Methods for Writing Equations

1. word equation – reactants and

products are represented by words

2. formula equation- reactants and

products are represented by

element

symbols and formulas

3. balanced chemical equation – a

formula equation using coefficients

to represent the number of atoms,

molecules, or formula units


C. Symbols Used in Writing Equations

1. --------> yields, forms, produces, reacts

to form 2. --------> reversible reaction (products <--------- react to re-form the

reactants)

3. symbols or words written above -----> a. triangle – reaction requires heat b. oC – indicates temperature required c. atm – indicate pressure is required d. symbol for element or formula for compound – catalyst is required


4. letters or symbols next to formula

a. letters

(s) – solid (l) – liquid

(g) – gas (aq) – aqueous solution

b. symbols

arrow point up – gas produced

arrow pointing down–precipitate forms


Chemical EquationsChemical Equations4 Al(s) + 3 O2(g)

---> 2 Al2O3(s)

This equation means

4 Al atoms + 3 O2 molecules ---produces--->

2 molecules of Al2O3

AND/OR

4 moles of Al + 3 moles of O2 ---produces--->

2 moles of Al2O3


http://www.youtube.com/watch?v=d58UcB_Yb2Q

1. Define the terms “reactants” and “products.” Give examples of each from a chemical equation.

2. What do all chemical reactions need?

3. What do you think EA stand for?

4. What role does a catalyst play in a chemical reaction?

http://www.youtube.com/watch?v=d58UcB_Yb2Q



II. CHEMICAL REACTIONS

A. Bonds and Chemical Reactions

1. bonds form, break or both

2. atoms combine, separate, rearrange

A + B A-B C-D C + D

A-B + C C-B + A C-D + B C-B + D

A-B + C-D A-D + C-B

Documents

Unit 1A ACS Chemistry in the Community Sixth Edition