Unit 2 What is Chemistry

Unit 2 What is Chemistry?

CHEMISTRY - the study of the structure and composition of matter, the physical and chemical changes it undergoes and the energy that is exchanged.

structure is the order in which the atoms are actually hooked together
composition is what different elements are actually in something
Matter is the physical "stuff" of the universe. It is defined as anything which has mass and occupies space. More recently it has been defined as anything having the property of inertia.

Law of Conservation of Matter: Matter can neither be created nor destroyed .

All matter can be classified into two categories--homogeneous and heterogeneous

-homogeneous means that it is one phase throughout; completely uniform

An example of something homogeneous is water--every portion of the water looks (and is) EXACTLY like every other portion of water; completely uniform throughout

-heterogeneous means that the matter is made up of more than one phase

An example of something heterogeneous is a chocolate chip cookie--you can see chocolate chips, pecans, cookie dough. etc,

I. HOMOGENEOUS SUBSTANCES CAN ONLY BE ONE OF THREE THINGS--elements, compounds or solutions

1. ELEMENT - matter composed of only one type of atom; the simplest form of matter; cannot be changed to another element except by a NUCLEAR reaction

· 112 have been discovered but only 109 have been named and their names accepted; only 88 elements are naturally occurring; all others are man made

· the symbol for an element is 1 capital letter OR 1 capital letter and 1 lower-case letter. Some elements are named by their English names (the element Carbon is symbolized by its English name: C) Some are named by their Latin names: Ex: The element Sodium is symbolized by its Latin name: Natrium: Na; Some other Latin based elements are lead: Pb (Plumbus); Iron; Fe (Fermium); Silver: Ag (Argent); Tin: Sn (Stannus)

2. COMPOUNDS are substances composed of more than one atom chemically joined together, water is a compound: H₂O, Sucrose is a compound: C₁₂H₂₂O₂₂; Oxygen is most often found as a compound: O₂.

· compounds can be changed to other compounds and separated by chemical

reactions only

· compounds do not have the same properties of the elements which make

them up. For example, water

· over 10 000 000 different compounds are known today, most of them organic

(from living things)

· the chemical formula for a compound will have more than 1 capital letter in it

because it contains more than one element

· the proportions of elements in a compound do not change or you have

changed the compound. For example H2O vs hydrogen peroxide!

3. SOLUTIONS are a uniform mix of two or more substances which are NOT chemically bonded and therefore, unlike compounds, each component retains its original identity and properties, you cannot see the particles of these two substances and thus a solution allows the transmittance of light.

A solution has TWO parts--

SOLUTE is the component which whose phase is changed. ONLY if both components are the same phase, the solute is the one in the LESSER quantity For example: Sugar and water

SOLVENT is the component which remains unchanged. ONLY if both components are the same phase, the solvent is the one in the GREATER quantity.

When two liquids are mixed, we describe their interaction as:

MISCIBLE: If they dissolve in each other completely and mix uniformly in any proportions An example of miscible liquids is vinegar and water.

IMMISCIBLE: If the two liquids do not dissolve in each other and form two distinct layers, they are said to be Examples of immiscible liquids are oil and water.

Alloy: When two metals are melted together, like gold and silver to make jewelry

Example 2-1:

Aluminum chloride is a white crystal. Alcohol is a clear liquid. When these are

mixed, a clear liquid solution results. What is the solvent? ______________

If there is 91% gold , 7 % silver and 3% copper in 22 kt gold, an alloy. What is the

solvent? What are the solutes? ________________________________________

II. HETEROGENEOUS SUBSTANCES ARE ALWAYS MIXTURES! They are not uniform in composition. There is more than one phase present.

Dry Heterogeneous Mixtures: made of dry particles of different types can be elements and/or compounds.

If a solution has particles in it, it is not technically called a solution anymore. There are two ways we name these types of heterogeneous mixtures:

Colloid: a mixture who’s particles are evenly distributed and bigger than the particles in a solution but smaller than the particles in a suspension

Suspension: a mixture who’s particles are so large that they settle out unless constantly agitated.

TO CLASSIFY MATTER, YOU MUST ALWAYS USE TWO WORDS--HOMOGENEOUS ELEMENT, HOMOGENEOUS COMPOUND, HOMOGENEOUS SOLUTION OR HETEROGENEOUS MIXTURE.

Example: 2-2

How would you classify the following substances?

Chemical changes involve a NEW substances being formed. These changes are usually not reversible; Examples of chemical changes are tarnishing, burning, digesting, rusting.

iv. a precipitate is formed (a precipitate is a solid product which forms in a chemical reaction)

Physical changes in matter will change its physical state but not its composition; frequently physical changes are reversible and are linked to changes in energy within matter. Examples: grinding, bending, dissolving, tearing, filtering; boiling & all physical state changes

Energy in matter is a very intangible thing to define. Probably the best definition is the capacity to do work or transfer heat.

Law of Conservation of Energy: Energy can neither be created nor destroyed only transferred to other forms.

The main differences in solids, liquids and gases is the proximity of their particles and the speed of movement between those particles. In solids, the particles are very close together, touching each other and packed tightly enough that the particles cannot move at all except to rotate on their axes. In liquids, the particles touch each other lightly but can slide past each other as the liquid FLOWS. In gases, the particles are completely independent and do not touch each other at all.

SOLIDS - have definite shape and definite volume; usually HIGH density; expands only slightly when heated; almost incompressible

LIQUIDS - has definite volume but not definite shape; usually is less dense than solids; expands more than solids when heated; almost incompressible; takes the shape of its

GASES - has neither definite shape nor definite volume; very LOW density; expands greatly

when heated; highly compressible; takes the shape of the container; flows freely

solid changing to a liquid ___________________liquid changing to a vapor _____________________

vapor changing to a liquid ___________________liquid changing to a solid _____________________

solid changing to a vapor ___________________vapor changing to a solid _____________________

Physical Properties of matter describe the substance itself (alone).There are two types of physical properties:

(1) Intensive properties do not change with amount; are used for identification, examples are: color, smell, etc including:

You must know how to apply the density formula to solving problems for density, mass and volume. Units: g/cm³ or g/ml

The density of lead is 11.35 g/cm³. What is the mass of a 10.0 cm³ piece of lead?

The mass of a 5.00 cm³ sample of clay is 11.0 g. What is the density of the clay?

If a solid piece of Calcium has a density of 4.0 g/cm³, what volume is 24g of that calcium?

Buoyancy: The tendency of a less dense substance to float in a more dense substance. Buoyancy increases as the difference between densities of two substances increases. Liquids have buoyant force, that is the measurement of how much the liquid pushes against the object.

Boats can be made of a variety of materials, including concrete. Concrete has a density of 10.5 g/cm³ and water has a density of 1 g/cm³. What is the best explanation for why a concrete boat will float in water?

Viscosity: the resistance of a fluid to flow. The strength of attraction between particle of a fluid determine how fast it flows. The faster it flows the lower the viscosity. Ex: Water flows faster than molasses, it has a lower viscosity.

b. Energy: the more energy a substance has between its particles the lesser its viscosity

Usually people buy motor oil with a high viscosity in the summer time and a motor oil with a lower viscosity for winter time. What is the best explanation for why this would be a good idea?

(2) Extensive properties depend on the amount of matter present; these change Constantly and therefore cannot be used for identification Examples of extensive properties are: Mass; Volume, Length, width, height, etc.

Chemical Properties of matter describe how the substance reacts with something else. Examples of chemical properties are "How does it react with acids?" "Does it burn?" "Does it react with water?”