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 – CO 2 Carbon monoxide -CO - (no subscripts since only one atom is present) Hydrogen peroxide –H2O2–H2O2 Methane – CH 4

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. Cl 2, C 3. – Molecules of compounds: (Different atoms in the molecule) e.g. H 2 O, HCl, H 2 SO 4.

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 compounds NaCl 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 Sodium Chlorine H 2 SO 4 3 Hydrogen Sulfur Oxygen = 7 NaOH CHCl 3 CaCO 3

Element or Compound? Copper

Element or Compound? Copper

Element or Compound? Table Sugar

Element or Compound? Table Sugar

Element or Compound? Diamond

Element or Compound? Diamond

Element or Compound? Salt

Element or Compound? Salt

Element or Compound? Neon Gas

Element or Compound? Neon Gas

Element or Compound? Pure Water

Element or Compound? Pure Water

Element or Compound? Aluminum

Element or Compound? Aluminum

Element or Compound? Silver

Element or Compound? Silver

Element or Compound? Oxygen

Element or Compound? Even Ozone (O 3 ) is an element, it only has one type of atom (O)!

Element or Compound? Chocolate

Element or Compound? Chocolate