Elements and Compounds

Matter

• Any thing with mass and volume

Matter can be classified based on what it is made of and how it behaves

Element

• A substance that cannot be broken down into simpler substances

• It contains only one kind of atom

There are about 118 known elements, but there are many

millions of chemical compounds.

Each element is represented by a Symbol

• The first letter is capitalized

• The second letter (if present) is lower case

• C- carbon• O- oxygen• Co- cobalt

Each element has unique characteristics

But when elements combine, they lose their unique characteristics and form a new substance with different

characteristics

= ?

Hydrogen + Oxygen = Water

We call this new substance a compound

• Compound- – a type of

substance made of atoms of two or more elements joined by chemical bonds

Compounds are represented by chemical formulas

• It will tell you:A. the elements in that compound

B. the number of atoms of that element

Writing a chemical formula for a compound

1. Write the symbol of the elements in that compound (H and O)

2. Use a subscript to identify how many atoms of each element are in the compound. (no subscript for a single atom)

Common Compound Formulas• Carbon Dioxide–CO2

• Carbon monoxide-CO - (no subscripts since only

one atom is present)• Hydrogen peroxide–H2O2

• Methane–CH4

Compounds can only be changed back into individual elements through a chemical reaction

Compounds usually form when a metal (green)and a non-metal (yellow) combine

Unit 7, 16

Molecules

• A molecule is a group of atoms joined together. • It is the smallest part of an element or

compound that can exist independently.

• There are two types of molecules:–Molecules of elements:

(All the same atoms in the molecule) e.g. Cl2, C3.–Molecules of compounds:

(Different atoms in the molecule) e.g. H2O, HCl, H2SO4.

Molecule examples

• Molecules of elements (top row)• Molecules of compounds (bottom row)

Unit 7, 19

Elements which form molecules• Elements that end in –ine and –gen exist as

diatomic (2 atom) molecules in their natural form.

Counting atoms in compoundsNaCl

• First identify which how many different elements are in the compound (2)

• Name those elements (Na- sodium, Cl- Chlorine)• Count how many atoms of each element are

present by looking at the subscript (1 of each)• Add up the atoms to determine the total

number of atoms in that molecule (2)

Formula # of elements

Name of elements

# of atoms of each element

Total # of atoms

 NaCl

 

 2

SodiumChlorine

11

 2

 H2SO4

 

 3

 HydrogenSulfur

Oxygen

 214

 2+1+4 =7

 NaOH

 

       

 CHCl3

 

  

     

 CaCO3

 

  

     

Element or Compound?

Copper

Element or Compound?

CopperCu

Element or Compound?

Table Sugar

Element or Compound?

Table Sugar

C 12H 22

O 11

Element or Compound?

Diamond

Element or Compound?

DiamondC

Element or Compound?

Salt

Element or Compound?

SaltNaCl

Element or Compound?

Neon Gas

Element or Compound?

Neon GasNe

Element or Compound?

Pure Water

Element or Compound?

Pure WaterH 2O

Element or Compound?

Aluminum

Element or Compound?

AluminumAl

Element or Compound?

Silver

Element or Compound?

SilverAg

Element or Compound?

Oxygen

Element or Compound?

O 2

Even Ozone (O3) is an element, it only has

one type of atom (O)!

Element or Compound?

Chocolate

Element or Compound?

Chocolate

C 7H 8N 4O 2