What was an element?  An element contains ONE KIND OF ATOM. One kind of atom only!

What was a compound?  A compound is made of different atoms that are CHEMICALLY BONDED together. More than one kind of atom!

Examples of compounds?  Water

Examples of compounds?  Carbon dioxide

Examples of compounds?  NaCl

What if we have a mixture?  How would you define a mixture? - A mixture contains different substances that are NOT BONDED together.

Examples of mixtures:          

ALLOYS ARE MIXTURES as well…  Mixture of two or more metals is called an alloy.

 Stainless steel is an alloy:  Fe 85%, Cr 14%, Ni 1% Some uses: Domestic appliances, furnace parts, valves, nuclear reactors

 Bronze is an alloy: Zn 85%, Sn 15% Some uses: Weapons and tools, decorations

 Solder is an alloy: Pb 67%, Sn 33% Some uses: to hold other materials together

 Brass is an alloy: Cu 60%, Zn 40% Some uses: Jewellery, household items, doorknobs

Alloys are…  are harder  are generally more resistant to chemicals than those of their component metals and that is why they are industrially preferred.

What are the differences between mixtures and compounds?

Formation of NaCl Na Cl 2

(bubbles seen)

 The chemical changes are usually called as “chemical reactions.”

Physical vs. Chemical change Physical ChangeChemical Change The material itself is the same before and after the change. New substances are formed. Usually easy to reverse.Usually difficult to reverse. Examples: Phase changes -melting, freezing, condensing,sublimation-, breaking, crushing, cutting, and bending. Examples: Burning, rusting,electrolysis, photosynthesis, explosions, respiration, rising of cakes, milk souring, cooking and food spoiling.