Chemical Formula Notes TEKS 8.5D recognize that chemical formulas are used to identify substances and determine the number of atoms of each element in chemical formulas containing subscripts TEKS 8.5F recognize whether a chemical equation containing coefficients is balanced or not and how that relates to the law of conservation of mass

Elements = pure substances = 1 type of atom (Example: H or H 2 )

Each elements has a chemical symbol represented with 1-2 letters. Si Na Fe O C He

Molecule = 2 or more atoms that are bonded Examples: O 2 (2 Oxygen) H 2 O (2 Hydrogen and 1 Oxygen)

Compound = 2 or more different atoms that are bonded Examples: H 2 O (2 Hydrogen and 1 Oxygen) CO 2 (1 Carbon and 2 Oxygen) NaCl (1 Sodium and 1 Clorine)

Why do element’s bond? To be happy! Atoms are not happy when their outer energy level is not full. When atoms bond they share electrons and get a full outer energy level.

8 O 15.9 Oxygen One Atom of O (Element) Not Happy  One Atom of O (Element) Not Happy 

O₂ 2 Atoms of Oxygen (Molecule) It’s happy! It’s full! It’s happy! It’s full!

Let’s Practice

Is Fe…… just an Element? – Yes (It has only 1 type of atom.) a molecule? – No (It doesn’t have 2 or more atoms.) a compound? – No (It doesn’t have different atoms.)

Is H 2 …… just an Element? – Yes (It has only 1 type of atom.) a molecule? – Yes (It has 2 or more atoms.) a compound? – No (It doesn’t have different atoms.)

Is CO₂ …… just an Element? – No (It has more than 1 type of atom.) a molecule? – Yes (It has 2 or more atoms.) a compound? – Yes (The atoms are different.)

Is NaCl …… just an Element? – No (It has more than 1 type of atom.) a molecule? – Yes (It has 2 or more atoms.) a compound? – Yes (The atoms are different.)

Is C 6 H 12 O 6 …… just an Element? – No (It has more than 1 type of atom.) a molecule? – Yes (It has 2 or more atoms.) a compound? – Yes (The atoms are different.)

Is B…… just an Element? – Yes (It has only 1 type of atom.) a molecule? – No (It doesn’t have 2 or more atoms.) a compound? – No (It doesn’t have different atoms.)

Is F 2 …… just an Element? – Yes (It has only 1 type of atom.) a molecule? – Yes (It has 2 or more atoms.) a compound? – No (It doesn’t have different atoms.)

A chemical bond, or electric force, holds the atoms together in a molecule.

The properties of a compound are totally different from the elements that make up the molecule. += carbonoxygen carbon dioxide

For example: Salt is composed of…. sodium (Na); a silvery metal; and chlorine (Cl); a stinky, green gas.

Salt=> (1 sodium, 1 chlorine) When the two elements bond to form NaCl, they form solid white crystals which you can eat! Na= poisonNaCl= yummy Cl= poison

Chemical formulas are used to show the ratio of elements in a compound. H 2 O 2:1 NaCl HCl

If more than 1 atom of an element is in the compound, it is shown with a subscript. O 2

H 2 O (Water) Has 2 atoms of hydrogen. Since oxygen has no subscript, there is only 1 atom of oxygen

Sometimes, substances contain more than 1 molecule of a compound.

Coefficients are written in front of the compounds IF there is more than 1 compound. 2H 2 O4H 2

2SO 3 means SO 3 + SO 3 2 molecules of sulfur oxide How many S atoms? –2–2 How many O atoms? –6–6

2SO 3 1. Add subscripts to elements without one. (If needed) 2. Multiple the Coefficient X Subscript S = 2 x 1 S = 2 O = 2 x 3 O = Sulfur Atoms + 6 Oxygen Atoms 8 TOTAL atoms