The Nature of Matter

 Notes 2-1 DESCRIBING MATTER

Matter  Anything that has mass and takes up space  Substance- single kind of matter that has a specific make-up and specific properties -Example: Salt or sugar -Non-Example: Muffin batter (the ingredients can vary)

Physical Properties of Matter  Can be observed without changing into another substance  Examples: Freezing point, melting point, density, texture, color, flexibility, solubility in water

Chemical Properties of Matter  Ability to change into a different substance  Examples: flammability, rusting, tarnishing, rising of bread in baking process

Elements  Pure substances that cannot be broken down into any other substance  Simplest substances  Is identified by its specific physical and chemical properties  Examples: Carbon, Oxygen, Gold, Silver, Aluminum

Atoms  Basic particle that makes up all elements  Having different atoms gives elements their unique properties  Atoms have a nucleus made up of positively charged protons and neutrally charged neutrons, and they are surrounded by a cloud of negatively charged electrons

Modeling an Atom  Pencil “lead” is made of mostly graphite, a form of carbon. Two ways to model atoms used in this presentation are shown here for carbon.

Chemical Bonds  Atoms combine by chemical bonds (a force of attraction between the electrons of 2 or more atoms)  Often form molecules- groups of 2 or more atoms held together by chemical bonds  Examples: H 2 O, O 2, CO 2

Modeling Molecules How many atoms are in each of these molecules?

Compounds  Pure substance made up of 2 or more elements chemically combined in a set ratio  Represented by a chemical formula which shows the elements in the compound and the ratio of atoms  When elements combine to form compounds, they have unique properties from those of the uncombined elements -Example: Hydrogen alone is a very combustible gas, Oxygen alone is a major supporter of combustibility, but when combined in the set 2:1 ratio H 2 O, they put out fires!

Ratios  A ratio compares two numbers. It tells you how much you have of one item compared to how much you have of another. For example, a cookie recipe calls for 2 cups of flour to every 1 cup of sugar. You can write the ratio of flour to sugar as 2 to 1, or 2:1.  The chemical formula for rust, a compound made from the elements iron (Fe) and oxygen (O), may be written as Fe 2 O 3. In this compound, the ratio of iron atoms to oxygen atoms is 2:3. This compound is different from FeO, a compound in which the ratio of iron atoms to oxygen atoms is 1:1.

Ratios  Practice Problem  What is the ratio of nitrogen atoms (N) to oxygen atoms (O) in a compound with the formula N 2 O 5 ? Is it the same as the compound NO 2 ? Explain.  N 2 O 5 contains two nitrogen atoms for every five oxygen atoms. Both N 2 O 5 and NO 2 are made up of only nitrogen atoms and oxygen atoms. However, the two compounds are different because NO 2 contains one nitrogen atom for every two oxygen atoms.

Mixtures  Made up of 2 or more substances that are not chemically combined  Differ from compounds because they do not have to have a set ratio, and each substance in mixture keeps its individual properties  Examples: Air, Soil, Salt water

Heterogeneous Mixtures  Hetero = different  Can see different parts of mixture  Examples: Soil, Salad Who can think of other examples?

Homogeneous Mixtures  Homo = same  Can’t see different parts of mixture, evenly mixed  Examples: Sugar/water solution, Air Who can think of other examples?

Separating Mixtures  Compounds are hard to separate  Mixtures are easy to separate since each component keeps its own properties  Look at figure 10 on page 66, it shows different ways to separate a mixture including using a magnet, filtering, distilling, and evaporating

LET’S REVIEW!!  What are some examples of chemical properties of matter?  Rusting, flammability, bread baking  What are some examples of physical properties of matter?  Density, melting, freezing, color, flexibility, hardness

LET’S REVIEW!!  What 2 things does a chemical formula show?  The elements present and the ratio of atoms  Give an example of an element.  Carbon, Oxygen, Nitrogen, Gold, Silver, etc.

 Notes 2-2 Changes in Matter

Physical Changes  Alters form or appearance of matter but does NOT change matter into a different substance  Examples: -Changes of state (solid to liquid, or liquid to gas, etc.) -Changes in shape or form (dissolving, chopping, cutting, bending, breaking, etc)

Chemical Changes A change in matter that produces one or more new substances Chemical change = chemical reaction New substances have properties different from original substances Examples: -burning of natural gas on gas stove (combustion) -rusting (oxidation)

Chemical Change

Law of Conservation of Matter  Matter is neither created nor destroyed in any physical or chemical change  No mass is lost, because during a chemical change, atoms are not lost or gained, just rearranged.

Conserving Matter The idea of atoms explains the law of conservation of matter. For every molecule of methane that burns, two molecules of oxygen are used. The atoms are rearranged in the reaction, but they do not disappear.

 Notes 2-3 Energy and Matter

ENERGY  Who remembers the definition of Energy?  The Ability to do WORK!

ENERGY  All chemical and physical changes include a change in energy

Law of Conservation of Energy  Energy is neither created nor destroyed  It is only transformed (changed from one form to another)

Forms of Energy  Forms of energy that include changes in matter are: Thermal Energy, Chemical Energy, Electromagnetic Energy, and Electric Energy

Thermal Energy  Temperature = average energy of random motion of particles of matter  Thermal Energy = total energy in all particles in an object  Thermal energy is related to temperature because the energy always flows from warm matter to cool matter  Endothermic Change = energy is absorbed Ex: Melting  Exothermic Change = energy is released Ex: Combustion

Chemical Energy  Stored in Chemical Bonds between atoms  Bonds are broken and new bonds formed  Ex: in foods, gas for cars, cells  Usually involve transformations between chemical energy and thermal energy, like when burning a match

Electromagnetic Energy  Travels through space as waves  Ex: Visible light, radiowaves, microwaves, x-rays, UV rays, infrared rays  Chemical changes can give off light (electromagnetic energy)  Microwaves thaw frozen food (physical change)

Electrical Energy  Energy of electrically charged particles moving from one place to another  Ex: electrons move from one atom to another in many chemical changes.  Ex: using electrolysis to separate water molecules into oxygen gas and hydrogen gas

Potential Vs Kinetic POTENTIAL ENERGY:  Energy waiting to be used  Ex: Food you eat KINETIC ENERGY:  Energy of Motion (Energy being used)  Ex: You taking notes!  Ex: You taking notes!

Transforming Energy Example 1:  Burning -Chemical change that transforms chemical energy and releases it as thermal energy (heat) and electromagnetic energy (light)

Transforming Energy Example 2:  Photosynthesis -Plants transform electromagnetic energy from the sun into chemical energy (sugar for plants)

Transforming Energy Example 3:  You Try!  What energy transformations occur when you ride a bike?  There is potential energy in the food you eat.  Your cells transform food into chemical energy your body can use.  Chemical energy is transformed to kinetic energy of moving muscles and thermal energy given off as heat.