The properties of compounds are often very different from the properties of the elements that make them up.
The following table compares the properties of two elements and the compound they make up when they are chemically combined. Element
Element z Fig. 11.1.2
Table salt (sodium chloride) on chips
Using models
Using building blocks, create models to represent the following: zz zz zz zz zz zz zz z z
An element containing five atoms. A mixture of three different elements.
A compound made of two different elements. A compound made of three different elements. A mixture of two different compounds. A mixture of an element and a compound. A mixture of two elements and a compound.
The following substances: water (H2O) and carbon dioxide (CO2).
Hints zz
z z zz zz
Each block represents an atom. An element contains just one type of atom.
A compound contains two or more types of atoms joined together. A mixture is two or more substances not joined together.
Molecules
Oxygen molecule
molecule Water
Carbon dioxide molecule
Atoms are nature’s building blocks. When atoms are joined together by bonds they make molecules.
Molecules are groups of two or more atoms bonded together. They are the smallest part of an element or compound that has the chemical properties of that element or compound.
molecule
Water olecule
Carbon dioxide molecule
Oxygen molecule
190
Oxygen: two oxygen atoms bonded together. We will look at how and why molecules bond later. Water
Familiar molecules include: zz zz zz
molecule z molecule Fig. 11.1.4 Examples of molecules
Carbon dioxide molecule
molecule Sulfur Sulfur
Water: two hydrogen atoms bonded to one oxygen atom. Sulfur
Carbon dioxide: one carbon atom bonded to two oxygen atoms. z
Sodium: very reactive with water. Stored in oil
Hydrogen: explosive gas, burns with a pop
Chlorine: a poisonous green gas
Oxygen: a gas needed to support combustion (burning)
Compound
Sodium chloride: a white crystal used to flavour food
Dihydrogen monoxide (water): a very important liquid needed to support life
