Changes in Matter
Elements are substances
that cannot be broken down into other substances by chemical or physical
means. They are pure substances made of only one kind of atom. Everything,
all matter, is made up of a small number of existing elements. The known
elements have been arranged and organized on a chart called The Periodic
Table.
Elements are chemically combined
in ways to create new substances. This somewhat like the alphabet, 26 known
letters. These letters can be joined to one another to produce an almost
infinite number of words.
Compounds are considered pure substances
made of two or more elements that have been chemically combined.
They are not easily taken apart by nomal means. When two elements
chemically combine the result or offspring of the combing may be vastly
different from its parent elements. Example: Hydrogen and fire = Explosion.
Oxygen and fire =Explosion. Two hydrogen atoms chemically combined to one
oxygen atom = water. Water plus fire results in no explosion. The fire
is either put out or the water turns to steam. This happens by two
types of bonding.
http://www.accessexcellence.org/RC/VL/GG/cov_IonicBs.html
Atoms can attain a more stable arrangement of electrons in their outermost
shell (valence electrons) by interacting with one another. An ionic
bond is formed when electrons are transferred from one atom to the
other. A covalent bond is formed when electrons
are shared between atoms. The two cases shown represent extremes; often,
covalent bonds form with a partial transfer (unequal sharing of electrons),
resulting in a polar covalent bond.
This bonding is the result of chemical changes.
A chemical change is a change which produces
a new substance. The new substance will have properties that are different
from the original substances. Burning is an example of a chemical change.
The gases and ashes have different properties from the original substance
before burning. The original substance cannot be restored from the gases
and ashes.
Chemical reactions are classified by the energy changes which accompany
them:
exothermic reaction-any chemical
change which releases energy (heat), or gives off more energy than it absorbs.
endothermic reaction-any chemical
change which absorbs energy
(heat). Chemical reactions involve the forming or breaking of chemical
bonds. The two primary types of chemical bonds are:
ionic bonds-the attraction of two
oppositely charged ions.
covalent bonds-bonds which form when two
or more atoms share electrons.
Electron Dot Diagrams, which are also
called Lewis dot diagrams, are very useful tools in Chemistry. They
will give you the ability to determine the type(s) of covalent bonds that
an element may make in certain situations. They can also be used
to predict the type of ion that an atom might make when it forms an ion.
Each dot diagram consists of; an elemental symbol, which represents the
kernel of the atom, and a group of 1-8 dots which shows the configuration
of the outer-most electron shell of the atom, also called the valence shell.
Below is an example of the proper Lewis dot
diagram for the element oxygen.
Electron dot diagrams, which are also called Lewis dot diagrams, are
very useful tools in Chemistry. They will give you the ability to
determine the type(s) of covalent bonds that an element may make in certain
situations. They can also be used to predict the type of ion that
an atom might make when it forms an ion. Each dot diagram consists
of; an elemental symbol, which represents the kernel of the atom, and a
group of 1-8 dots which shows the configuration of the outer-most electron
shell of the atom, also called the valence shell.
for more (http://www.fordhamprep.com/gcurran/sho/sho/lessons/lesson38.htm)
The original substances in a chemical reaction are called reactants.
The new substance is called the product.
Another way to classify chemical reactions is as: synthesis, decomposition,
single replacement, or double replacement.
Synthesis reaction-any chemical
reaction in which a single compound is formed from a combination of two
or more elements or compounds.
Middle grades explanation- Mr. Blue went to the dance. Ms. Red went
to the dance. They left as a couple.
Decompositionreaction-any reaction
in which a compound is broken down into two or more elements or compounds.
Decomposition reactions usually require the input of energy. Therefore,
they are usually endothermic.
Middle grades explanation- The couple of Blue Red went to the dance
together.Something happened at the dance and they left as 2 indivisuals.
Single replacement reaction-a reaction
in which an element in a compound is replaced by another element. 
Middle grade explanation- Single Ms. Blue went to the dance and
couple Red Yellow did also. However Ms.Blue prefered Red. They left as
a couple and Yellow left the dance alone. (skank or boyfriend stealer reaction)
D. double replacement reaction--a reaction is which an element in one
compound is exchanged with an element in another compound.
Middle grades explanation-Two couples go to the dance. They swap partners.(Jerry Springer or
Redneck reaction)
Chemical equations a
stament that uses symbols, formulas,and numbers to stand for a chemical
reaction. A chemical formula
is the way to write the kinds and numbers of atoms in a compound. The amount
of stuff you start with is the amount that you will end up with. This is
The Law of Conservation of Matter. It states that matter is neither created nor destroyed. The mass of the product is always equal to the mass of the reactants. This law causes chemical equations to be balanced.
A balanced equation is like a recipe. It tells you the proportional
quantities of each substance involved. The coefficients that appear to
the left of each formula can be interpreted as molecules. The following
rules should be used when balancing a Chemical Equation by inspection:
1.Never touch subscripts when balancing equations since that will change
the composition and therefore the substance itself.
2.Write all reactants on the left and all products on the right side
of the equation arrow. Make sure you write the correct formula for each
element.
3.Use coefficients in front of each formula to balance the number of
atoms on each side.
4.Multiply the coefficient of each element by the subscript of the
element to count the atoms. Then list the number of atoms of each element
on each side.
It is often easiest to start balancing with an element that appears
only once on each side of the arrow. These elements must have the same
coefficient. Next balance elements that appear only once on each side but
have different numbers of atoms. Finally balance elements that are in two
formulas in the same side.
Example
NH3 + O2 yields NO + H2O
N appears once on both sides in equal numbers, so the coeficient for
NH3 is the same as for NO.
Next look at H which appears only once on each side but has different
numbers of atoms, 3 on the left and 2 on the right. The least common multiple
of 3 and 2 is 6, so rewrite the equation to get 6 atoms of H on both sides:
2NH3 + O2 yields NO + 3H2O
There are 2 oxygen atoms on the left and 5 on the right — the least
common multiple of 2 and r is 10, so rewrite the equation as:
2NH3 + 5O2 yields 4NO + 6H2O
Now count the atoms on each side:
2 N yields 4 N
6 H yields 12 H
10 O yields 10 O
If you double the N and H on the left the equation will be balanced:
4NH3 + 5O2 yields 4NO + 6H2O
Double-check:
4 N yields 4 N
12 H yields 12 H
10 O yields 10 O
Mixtures-are two or more substances that
are not chemically combined (Example- trailmix). In a mixture all the parts
keep their properties. (Example -In trailmix the peanuts stay peanuts and
the M&Ms stay M&Ms).
Types of Mixtures
Mixtures can be divided into two main subsets:
Heterogenous and Homogenous
Heterogenous mixtures do not appear to
be the same throughout. fruitcake, trailmix, as well as oil and vinegar
are all heterogeneous mixtures. The particles are large enough to be seen
and can be separated from the mixture.
Homogenous mixtures are very well mixed.
Solutions are homogeneous mixtures. In a solution
one substance is dissolved in another. The particles in a solution are
atoms, ions, or molecules. The particles are obviously too small to be
seen and will not separate out on standing. Solutions have two parts.
SOLVENT- THE SUBSTANCE WHICH DOES THE DISSOLVING SOLUTE- THE SUBSTANCE
WHICH GETS DISSOLVED
(Example- coolaid- the water is the solvent the coolaid power and sugar
are the solutes)
Water is often called the universal solvent because it dissolves so
many materials. Substances (like oil) which do not dissolve in water are
called insoluble.
Suspension- a heterogeneous mixture in which the particles are large
enough to be seen by a microscope or the unaided eye (eventually, they
settle out of the mixture). Example: stirring a teaspoon of dirt in a glass
of water.
Colloid- a mixture where the size of particles in the mixture are between
those of a solution and a suspension. NOTE: The particles appear evenly
distributed. Examples: fog, cheese, butter, jellies, whipped cream.
Often scatter light and are milky and translucent
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