Post on 17-Dec-2015
transcript
= anything that occupies space and has mass
= may exist as a - pure substance (only one kind of
matter) either an element or compound - mixture (two or more kinds of
matter)
The study of matter– Its composition and properties– How it can be changed into something
new
is called CHEMISTRY!!
SO….To gain an understanding of the how some
things work, why oil and water don’t mix, why salt and sugar dissolve in water, how solutions are made or how pH is measured a basic understanding of some the basic
principles of chemistry is necessary
Areas of Chemistry
• General Chemistry• Organic Chemistry• Biochemistry• Inorganic Chemistry• Environmental Chemistry• Physical Chemistry• Nuclear Chemistry
Pure Substance = sample of matter with only one component
• Elements = pure substances that cannot be broken down into simper substances with different properties
• Compounds = a pure substance made up of two or more elements that are chemically combined in a fixed proportion by mass
What are Elements Made Of?
• Atoms are the basic structural unit– Are the smallest particle of an
element – Are so small that they cannot
be visualized even w/sophisticated microscopes
– About 2 billion atoms will fit on a period.
• All the atoms of given element are essentially the same
Elements – Building blocks of matter– Simplest type of pure substances from
which more complex matters are built– Presently 114 known elements– 90 of them are naturally occurring, rest
are man-made– Every element has its own unique set of
physical and chemical properties– 90% of the universe is hydrogen and 70%
of the earth’s crust is made up of oxygen and silicon
– Many are necessary in biological systems
Elements in percent by mass in (a) Earth's crust (including oceans and atmosphere) and (b) the
human body.
Elements on the Periodic Table
• What is the periodic table?-a chart that shows all of the known elements-give information about each element
Periodic Table
Why Know About the Periodic Table??
• The periodic table is the most important chemistry reference there is.
• It arranges all the known elements in an informative array.
• Its main use is to predict the chemical properties of an element based on where it is located on the table.
• People familiar with how the table is put together can quickly determine a significant amount of information about an element.
Some Common Elements & Their SymbolsCarbon C Aluminum Al Copper Cu (cuprum)
Fluorine F Barium Ba Iron Fe (ferrum)
Hydrogen H Calcium Ca Lead Pb (plumbum)
Iodine I Chlorine Cl Mercury Hg (hydragyrum)
Nitrogen N Helium He Potassium K (kalium)
Oxygen O Magnesium Mg Silver Ag (argentium)
Sulfur S Silicon Si Tin Sn (stannum)
Think Inside the Box
When you look at the periodic table, you should notice that each box represents a different element, and each box contains vital information about the element, – Name– symbol– atomic number– atomic mass
6C
Carbon
12.011
• The top number is the atomic number.• Every element has its own unique atomic
number.
• The large letter is the element's symbol
• Just below that is the element's name.
• Each element has its own unique symbol and name.
• Below the name is the element's atomic mass.
• The atomic mass essentially gives you an estimate of how massive one atom of that element is
3 Main Categories of Elements
• Metals• Non-Metals• Metalloids
Metals
• On the left side of the table• All are solid except for mercury• Described as shiny, ductile (most
metals can be drawn out into thin wires), malleable (most metals can be hammered into thin sheets )
• All are good conductors of electricity• All are good conductors of heat
Non-metals
• On the right side of the periodic table• Some are solid, some are gases.• Bromine is a liquid• Under most conditions are not good
conductors of heat or electricity
Metalloids (semi-metals)
• Elements along the stair-step line• These elements display the
properties of metals and non-metals, depending upon the conditions.
Compounds• Compounds are pure
substances made up of 2 or more different elements in a different proportion.
• Each is put together so that every unit of that compound is identical to every other unit
• They are different from every other compound
Units of a Compound – they are all the same
Examples of Compounds
• Water - made up of hydrogen and oxygen
• Carbon dioxide – made up of carbon and oxygen
• Rust – made up of iron and oxygen• Sugar – Made up of carbon, hydrogen
and oxygen
Naming Compounds
• Chemical formula – describes exactly what elements and the number of atoms of each element occurs in the smallest particle of that compound.
• We identify what elements are present by their symbol
• How many of those elements present are indicated by the subscript following the symbol.
Chemical Formulas
• Water = H20
means that each unit of water contains 2 atoms of hydrogen and one atom of oxygen
• Sugar (sucrose)= C12H22011
How many atoms of each element are in a unit of sugar?
C12H22011
Mixtures
= a combination of two or more substances in which each retains its own identity
- May be a homogenous mixture OR- May be a heterogeneous mixture
Mixtures• Homogeneous mixtures -
– A mixture of two or more components that is uniform throughout.
– Every portion of the sample is identical- Components cannot be filtered out or separated
out or will not settle out- Can exist as a solid, liquid or gas– For example
• brass (a mixture of zinc & copper.)• Salt water (Sodium chloride dissolved in water)• air (a uniform mixture of N2, O2, CO2 and trace gases)
Mixtures• Heterogeneous mixtures – have 2 or more components- components have distinct regions with
definite boundaries- can be separated by some physical
property- can exist as liquids or solids
For example:• Soil – bits of sand, black soil, organic matter• Blood - appears homogeneous but it is actually
a heterogeneous mixture of red and white blood cells that are visible under a microscope.
In-between Classification
• Colloid or colloidal dispersion - mixture that is not quite heterogeneous and not quite homogeneous
• Example – milk is a colloid. The particles are too small to be seen unaided but are small enough that they will not settle out
• Others = fog, smoke, whipped cream, mayonnaise, marshmallows
Fat In Milk (Globules Magnified)
Skim-milk Whole Milk
Cream
Another type of Mixture• Suspension – where
particles are large enough that they will eventually settle out
• mixture in which the particles of one substance are scattered in another without dissolving
• Example – making a clay pot. The clay particles in the mixture eventually settle out.
Differentiating between mixtures
A true solution, will appear clear when a light is shown through it.
Differentiating between mixtures
Colloidal dispersion - very small particles spread throughout the liquid which are large enough to reflect light, but not large enough to be seen individually. -may look either clear or cloudy in ordinary room light. -particles in remain dispersed in the liquid and will not settle out.
=easiest categorized by it’s physical states either a solid, liquid or gas
States of Matter• Solids – have a definite shape and
volume• Individual particles are arranged very
close together so that there is very little motion and no room for compression
• Crystalline solids – particles arranged in regular, systematic patterns (sugar, salt)
• Amorphous solids – some freedom of motion of the particles ( glass, rubber, wax)
Physical States of Matter
• Liquids – have fixed volume but variable in shape.
• Particles are not held together as rigidly as the solid state
• They can slide past one another so the sample is said to flow or be fluid
• They take on the shape of the container
• Volume of sample remains constant
Physical States of Matter
• Gases – have no volume or fixed shape• Particles are not attracted to each other
but rather expand to fill any conatiner• Particles are in constant random motion
and move about independently• Distance between them is greater than
in a solid or liquid.• Can be compressed into a smaller
space, within limits
• All types of matter contain energy.• More specifically kinetic energy = the
energy of motion• How much kinetic energy is dependent on
the mass of the individual particles and the velocity at which they are moving.
The Amount of Kinetic Energy
• Solid – very little kinetic energy
• Liquid - more random movement of particles so there is more energy
• Gas – particles move constantly and independently. Generally – has more energy than a solid or liquid
Conversion From One Physical State to Another
Ice to Water to Gas
Solid - below 0ºC (freezing point)Liquid – between 0ºC and 100ºC
(melting point)Gas (steam) – converted to once
it reaches 100ºC (boiling point)
Phase Changes as Temperature Increases
Temperature
• Is the measure of the average Kinetic Energy of the particles in a particular sample
• Temperature rises when energy is added.
• When energy leaves, temperature decreases
Properties Of Matter
• Physical properties– those that can be observed or measured without changing the composition of the sample of matter.
• When a physical property is changed we say it is a physical change
A physical change is a change in the form of matter but not in its chemical identity. No new compounds are formed during a physical change.
What is a Physical change?
• Melting is a physical property
• When ice melts and becomes water this is a physical change.
• What about tearing a big piece of paper into smaller pieces or chopping wood into smaller pieces?
Physical change
• Have only made the size of the sample smaller
Chemical properties – describes the ability of a sample of matter to be converted into a different sample of matter
All of the original substance must be accounted forLaw of Conservation of Matter – matter may not be
created or destroyed in a chemical transformation.
This chemical change (transformation) involves the rearrangement of the atoms to form some new type(s) of matter.
Chemical Changes
• Involve energy• The energy holds all the parts of the
substance together like glue• Before they are changed into
something new the pieces have to be pulled apart – this requires energy
• When they are reassembled again into a new substance the “glue” or energy holds them together
Questions to ask – 1. Does it burn in air?2. Does it decompose when heated?3. What happens when it is placed in acid?4. What other chemicals will the sample of
matter react with and what is produced?
• Chemical changes are usually irreversible.New compounds are formed during a chemical change
Physical and chemical properties…
• Describe a sample of matter• In most cases is does not matter
what the size of the matter is it will still have the same properties
• These properties are called intensive properties
.
Physical Properties = heavy, malleable, ductile, silvery-white color and can take and retain a magnetic fieldChemical Properties =
The rusting of iron is an example of a chemical change.Reaction = moisture and oxygen in
the air forms a compound called an oxideThe rust has a different chemical
composition than the initial iron
Describing an Iron Nail
Burning CandleChemical or Physical Change?
Bolt in Strong AcidChemical or Physical Change?
Penny in SolutionChemical or Physical Change?
Crushing/GrindingChemical or Physical Change?
Cooking an eggChemical or Physical Change?
Breaking Glass
before after
Breaking GlassChemical or Physical Change?
Chopping FoodChemical or Physical Change?