CHEMISTRY Chapter 1: Introduction Section 2: Describing matter
The Nature of Matter. Notes 2-1 DESCRIBING MATTER.
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Transcript of The Nature of Matter. Notes 2-1 DESCRIBING MATTER.
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: H2O, O2, CO2
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 H2O, 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 Fe2O3. 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 N2O5? Is it the same as the compound NO2? Explain.
N2O5 contains two nitrogen atoms for every five oxygen atoms. Both N2O5 and NO2 are made up of only nitrogen atoms and oxygen atoms. However, the two compounds are different because NO2 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 2-3Notes 2-3Energy and Energy and
MatterMatter
ENERGYENERGY
Who Who rememberremembers the s the definition definition of Energy?of Energy?
The The Ability Ability to do to do WORK!WORK!
ENERGYENERGY
All chemical and physical All chemical and physical changes include a change in changes include a change in energyenergy
Law of Conservation of Law of Conservation of EnergyEnergy
Energy is neither created nor Energy is neither created nor destroyeddestroyed
It is only transformed It is only transformed (changed from one form to (changed from one form to another)another)
Forms of EnergyForms of Energy
Forms of energy that include Forms of energy that include changes in matter are: Thermal changes in matter are: Thermal Energy, Chemical Energy, Energy, Chemical Energy, Electromagnetic Energy, and Electromagnetic Energy, and Electric EnergyElectric Energy
Thermal EnergyThermal Energy
Temperature = average Temperature = average energy of random energy of random motion of particles of motion of particles of mattermatter
Thermal Energy = total Thermal Energy = total energy in all particles in energy in all particles in an objectan object
Thermal energy is Thermal energy is related to temperature related to temperature because the energy because the energy always flows from warm always flows from warm matter to cool mattermatter to cool matter
Endothermic Change Endothermic Change = energy is absorbed= energy is absorbed
Ex: MeltingEx: Melting
Exothermic Change = Exothermic Change = energy is releasedenergy is released
Ex: CombustionEx: Combustion
Chemical EnergyChemical Energy
Stored in Chemical Bonds between atomsStored in Chemical Bonds between atoms
Bonds are broken and new bonds formedBonds are broken and new bonds formed
Ex: in foods, gas for cars, cellsEx: in foods, gas for cars, cells
Usually involve transformations between chemical Usually involve transformations between chemical energy and thermal energy, like when burning a energy and thermal energy, like when burning a matchmatch
Electromagnetic EnergyElectromagnetic Energy
Travels through space as wavesTravels through space as waves
Ex: Visible light, radiowaves, microwaves, x-rays, Ex: Visible light, radiowaves, microwaves, x-rays, UV rays, infrared raysUV rays, infrared rays
Chemical changes can give off light Chemical changes can give off light (electromagnetic energy)(electromagnetic energy)
Microwaves thaw frozen food (physical change)Microwaves thaw frozen food (physical change)
Electrical EnergyElectrical Energy
Energy of electrically charged particles moving Energy of electrically charged particles moving from one place to anotherfrom one place to another
Ex: electrons move from one atom to another in Ex: electrons move from one atom to another in many chemical changes.many chemical changes.
Ex: using electrolysis to separate water molecules Ex: using electrolysis to separate water molecules into oxygen gas and hydrogen gasinto oxygen gas and hydrogen gas
Potential Vs KineticPotential Vs Kinetic
POTENTIAL ENERGY:POTENTIAL ENERGY:
Energy waiting Energy waiting to be usedto be used
Ex: Food you Ex: Food you eateat
KINETIC ENERGY:KINETIC ENERGY:
Energy of Energy of Motion (Energy Motion (Energy being used)being used)
Ex: You taking Ex: You taking notes! notes!
Transforming Energy Transforming Energy Example 1:Example 1:
BurningBurning
-Chemical change -Chemical change that transforms that transforms chemical energy chemical energy and releases it as and releases it as thermal energy thermal energy (heat) and (heat) and electromagnetic electromagnetic energy (light)energy (light)
Transforming Energy Transforming Energy Example 2:Example 2:
PhotosynthesisPhotosynthesis
-Plants transform -Plants transform electromagnetic electromagnetic energy from the energy from the sun into chemical sun into chemical energy (sugar for energy (sugar for plants)plants)
Transforming Energy Transforming Energy Example 3:Example 3:
You Try!You Try!
What energy What energy transformations transformations occur when you ride occur when you ride a bike?a bike?
There is potential There is potential energy in the food you energy in the food you eat.eat.
Your cells transform Your cells transform food into chemical food into chemical energy your body can energy your body can use.use.
Chemical energy is Chemical energy is transformed to kinetic transformed to kinetic energy of moving energy of moving muscles and thermal muscles and thermal energy given off as heat.energy given off as heat.