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.