elements and compounds middle school

Elements and CompoundsNotes 1/20/10

Elements

Atoms are the smallest parts of

Everything that exists is made up of different combinations of elements. All of the elements that are known are listed by their properties on the periodic table.The smallest little piece of any element that you can have is called an ATOM.Metals on the left, nonmetals on the right, similar properties

All atoms of an element have the same # of protons

The # of protons in the atoms of a substance is what makes it different and unique.That is why it is used as the atomic number to identify an element on the periodic table. Ex: The only difference between Fluorine and Neon is 1 proton.

Atoms like to share electrons

This takes energy

This bonds them together

This creates a new substance called a molecule

Some atoms like to pair up with other atoms. Some atoms do this easily (like Na) and others don’t (C). This depends on their reactivity. Other atoms don’t do it at all (noble gases).When they pair up, it has to do with giving each other electrons. When they do that, it creates a CHEMICAL BOND that makes them stick together.

You cannot separate atoms that have been bonded together by physical means (like separating a mixture). In order to separate atoms, or bond them together, or make them rearrange, they have to go through a chemical reaction. It takes energy, sometimes a lot of it, to separate atoms that are sharing electrons.

New Substance = New Properties

+

Sodium(Na)

Chlorine(Cl)

Sodium Chloride(NaCl)

A chemical reaction is when a chemical change takes place and there are new chemical bonds formed. When this happens, the new compound has totally different physical and chemical properties, because it has been changed (that’s why a change in properties indicates a chemical change).

+

Sodium Atoms Chlorine AtomsSodium Chloride

Molecules

A chemical reaction is when a chemical change takes place and there are new chemical bonds formed. When this happens, the new compound has totally different physical and chemical properties, because it has been changed (that’s why a change in properties indicates a chemical change).

Molecules are the smallest parts of

COMPOUNDS

Pure SubstancesElements OR compounds have only one type of component

SugarC6H12O6

GoldAu

That’s what makes them PURE SUBSTANCES

Has only one type of component (atom)

Mixture Pure Substance

Chemical Reactions...

Reactants

Yields

Products

This is an example of how a chemical reaction works. Imagine each person is a type of atom. They break up with whatever partner they are bonded with and reorganize with new partners. Are there the same total number of people (atoms) at the beginning and the end? YES They have just changed places. This is how the conservation of mass is. You aren’t destroying anything during a chemical reaction, you are just changing the properties of the substances by arranging the atoms differently.

Chemical Reactions...

ENERGYADDED

ENERGYRELEASE

Start with3 total people

(3 atoms)

End with3 total people

(3 atoms)

This is an example of how a chemical reaction (change) works. Imagine each person is a type of atom. They break up with whatever partner they are bonded with and reorganize with new partners. Are there the same total # of people (atoms) at the beginning and at the end? YES They have just changed places. This is how the conservation of mass is. You aren’t destroying anything during a chemical reaction, you are just changing the properties of the substances by arranging the atoms differently.

Chemical Reactions...

ENERGYADDED

ENERGYRELEASE

It takes energy to start a chemical reaction, because it requires energy to break bonds (you are doing work on the bonds). When the bonds reform to make new substances, it releases chemical energy stored in the compounds.If it absorbs more energy than it releases, the temperature drops because it is using more energy than it is releasing (endothermic)If breaking the bonds doesn’t require much energy, but it releases more, then the temperature raises (exothermic)

Think back...How does what we have talked about relate to the chemical reaction you researched?

Vinegar + Baking SodaWhat elements make up the molecules of vinegar and baking soda?

How were the water, carbon dioxide, and sodium acetate made?

How many reactants and products did you have?

Was this reaction endothermic or exothermic?

When the new substances were made, did it create or destroy the matter?

WHAT FACTORS DO YOU THINK COULD EFFECT HOW FAST THE CHEMICAL REACTION TOOK PLACE?