Chapter 2: Elements of Chemistry Table of Contents Section 2.1: Matter has Physical and Chemical...

Chapter 2: Elements of Chemistry

Table of ContentsTable of Contents

Section 2.1: Matter has Physical and Chemical Properties & ChangesSection 2.2: Atoms are the Fundamental Components of ElementsSection 2.3: Atoms can combine to Form CompoundsSection 2.4: Most materials are MixturesSection 2.5: Chemists Classify Matter as Pure or ImpureSection 2.6: Elements are Organized in the Periodic Table by their Properties

• A physical property is a characteristic that you can observe without changing or trying to change the composition of the substance.

• How something looks, smells, sounds, or tastes are all examples of physical properties.

Physical Properties

Physical and Chemical PropertiesPhysical and Chemical Properties

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Properties are…• Words that describe matter (adjectives)• Physical Properties- a property that can be

observed and measured without changing the material’s composition.

• Examples- color, hardness, m.p., b.p.• Chemical Properties- a property that can only

be observed by changing the composition of the material.

• Examples- ability to burn, decompose, ferment, react with, etc.

• You can detect many physical properties with your senses.

• For example, you can see the color and shape of an object.

Using Your Senses


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• You can also touch it to feel its texture.

• You can smell the odor or taste the flavor of some matter.

• To describe a sample of matter, you need to identify its state. This property, known as the state of matter, is another physical property that you can observe.

State


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Click image to view movie.

• Perhaps you are most familiar with the three states of water.

State


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• You can drink or swim in liquid water.

State


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• You use the solid state of water, which is ice, when you put ice cubes in a drink.

• Although you can’t see it, water in the gas state is all around you in the air.

States of MatterStates of Matter

Solid

Liquid

Gas

Definite Volume?

YES

YES

NO

Definite Shape?

YES

NO

NO

Result of a TemperatureIncrease?

Small Expans.

Small Expans.

Large Expans.

Will it Compress?

NO

NO

YES

4th state: Plasma - formed at high temperatures; ionized phase of matter

as found in the sun

Three Main Phases – page 41

Copper Phases - Solid

Copper Phases - Liquid

Copper Phases – Vapor (gas)

• Some physical propertied depend on the size of the object.

Size-Dependent Properties


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Describing Matter• Properties used to describe matter can be

classified as:

1) Extensive – depends on the amount of matter in the sample

- Mass, volume, calories are examples

2) Intensive – depends on the type of matter, not the amount present

- Hardness, Density, Boiling Point

• Another physical property that depends on size is mass, which is a measurement of how much matter it contains.



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• Weight is a measurement of force.



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• If you were to travel to other planets, your weight would change but your size and mass would not.

• Weight depends on the mass of the object and on gravity.

• Another physical property, density, does not depend on the size of an object.

Size-Independent Properties


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• Density measures the amount of mass in a given volume.

• To calculate the density of an object, divide its mass by its volume.

• Another property, solubility, also does not depend on size.

Size-Independent Properties


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• Solubility is the number of grams of one substance that will dissolve in 100 g of another substance at a given temperature.

• The temperature at which a solid changed into a liquid is called its melting point.

Melting and Boiling Point


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• The temperature at which a liquid changes into a gas is called its boiling point.

• Some materials pull iron toward them.

Magnetic Properties


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• These materials are said to be magnetic.

• Lodestone is a rock that is naturally magnetic.

• Some materials can be made into magnets.

• Some properties of matter cannot be identified just by looking at a sample.

Chemical Properties


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• For example, the ability to burn is a chemical property.

• A chemical property is a characteristic that cannot be observed without altering the substance.

Physical Changes• A physical change is one in which the form

or appearance of matter changes, but not its composition. For example, a frozen lake has experienced a physical change.

• Although the water changes states due to change in temperature, it is still made of the elements hydrogen and oxygen.

Physical and Chemical ChangesPhysical and Chemical Changes

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Changing Shape

• Crumpling a sheet of paper into a ball causes a physical change.

• Whether it exists as one flat sheet or a crumples ball, the matter is still paper.


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• Generally, whenever you cut, tear, grind, or bend matter, you are causing a physical change.

Dissolving• When you add sugar to iced tea, the sugar

only seems to disappear.• Actually, the sugar dissolves.


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• When this happens, the particles of sugar spread out in the liquid.

• The composition of the sugar stays the same, which is why the iced tea tastes sweet.

• Only the form of the sugar has changed.

Changing State

• A physical change occurs when matter changes from one state to another.


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• When an ice cube melts, for example, it becomes liquid water.

• Matter can change from any state to another.

• Freezing is the opposite of melting.

• During freezing, a liquid changes into a solid.

Changing State


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• A liquid also can change into a gas. This process is known as vaporization.

• During the reverse process, called condensation, a gas changes into a liquid.

Changing State

• In some cases, matter changes between the solid and gas states without ever becoming a liquid.


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• The process in which a solid changes directly into a gas is called sublimation.

• The opposite process, in which a gas changes into a solid, is called deposition.

Chemical Changes• The explosion of

fireworks is an example of a chemical change.


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• During a chemical change, substances are changed into different substances.

• In other words, the composition of the substance changes.

Chemical Changes• When iron in steel is exposed to oxygen and

water in air, iron and oxygen atoms combine to form the principle component in rust.


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• In a similar way, silver coins tarnish when exposed to air.

Signs of Chemical Changes

• Physical changes are relatively easy to identify.


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• If only the form of a substance changes, you have observed a physical change.

• How can you tell whether a change is a chemical change?


• You have witnessed a spectacular chemical change if you have seen the leaves on a tree change from green to bright yellow, red, or orange.


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• But, it is not a change from a green pigment to a red pigment, as you might think.

• Pigments are chemicals that give leaves their color.

Signs of Chemical Changes• The green pigment that you see during the

summer is chlorophyll (KLOHR uh fihl).


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• In autumn, however, changes in temperature and rainfall amounts cause trees to stop producing chlorophyll.



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• The chlorophyll already in the leaves undergoes a chemical change into colorless chemicals.

Signs of Chemical Changes• The pigments that produce fall colors have

been present in the leaves all along.


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• However, in the summer, chlorophyll is present in large enough amounts to mask these pigments.

• In the fall, when chlorophyll production stops, the bright pigments become visible.

Color

• The reason a half-eaten apple turns brown is that a chemical change occurs when the apple is exposed to air.


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• The color of food changes as it is cooked because a chemical change occurs.

Energy

• Another sign of a chemical change is the release or gain of energy by an object.


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• Many substances must absorb energy in order to undergo a chemical change.

• For example, energy is absorbed during the chemical changes involved in cooking.

Energy

• Another chemical change in which a substance absorbs energy occurs during the production of cement.


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• This process begins with the heating of limestone.

• When it absorbs energy during heating, it undergoes a chemical change in which it turns into lime and carbon dioxide.

Energy

• Energy also can be released during a chemical change.


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• Fireworks release energy in the form of light that you can see.

Energy


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• A chemical change within a firefly releases energy in the form of light.

• Energy is released when sodium and chlorine are combined and ignited.

• During this chemical change, the original substances change into sodium chloride, which is ordinary table salt.

Odor• When eggs and other foods spoil, they

undergo chemical change.


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• The change in odor is a clue to the chemical change.

• When you smell an odd odor in foods, such as chicken, pork, or mayonnaise, you know that the food has undergone a chemical change.

• You can use this clue to avoid eating spoiled food and protect yourself from becoming ill.

Gases or Solids• The formation of a gas is a clue to a chemical

change.


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• The formation of a solid is another clue to a chemical change.

• A solid that separates out of a solution during a chemical change is called a precipitate.

• A common precipitate forms when a solution containing sodium iodide is mixed with a solution containing lead nitrate.

Not Easily Reversed

• Physical and chemical changes are different from one another.


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• After solid ice melts into liquid water, it can refreeze into solid ice if the temperature drops enough.

• Freezing and melting are physical changes.

Not Easily Reversed• The substances produced during a chemical

change cannot be changed back into the original substances by physical means.


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• Wood that has changed into ashes and gases cannot be restored to its original form as a log.

Not Easily Reversed


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• The substances that existed before the chemical change no longer exist.

Chemical Versus Physical Changes• In a physical change, the composition of a

substance does not change.


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• In a chemical change, the composition of a substance does change.

• When a substance undergoes a physical change, only its form changes.

• In a chemical change, both form and composition change.

Chemical Versus Physical Changes

• When substances like wood and copper undergo physical changes, the original wood and copper still remain after the change.


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• When a substance undergoes a chemical change, however, the original substance is no longer present after the change.

Chemical Versus Physical Changes• Instead, different substances are

produced during the chemical change.


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• When wood and copper undergo chemical changes, wood and copper have changed into new substances with new physical and chemical properties.

Chemical Versus Physical Changes


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• Physical and chemical changes are used to recycle or reuse certain materials.

Conservation of Mass

• During a chemical change, the form or the composition of the matter changes.


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• The particles within the matter rearrange to form new substances, but they are not destroyed and new particles are not created.


• The number and type of particles remains the same.


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• As a result, the total mass of the matter is the same before and after a physical or chemical change. This is known as the law of conservation of mass.

Conservation of Mass• In many chemical changes

in which mass seems to be gained or lost, the difference is often due to a gas being given off or taken in.


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• If the gases could be contained in a chamber around the candle, you would see that the mass does not change.


• The scientist who first performed the careful experiments necessary to prove that mass is conserved was Antoine Lavoisier (An twan . luh VWAH see ay) in the eighteenth century.


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• It was Lavoisier who recognized that the mass of gases that are given off or taken from the air during chemical changes account for any differences in mass.

11Section CheckSection Check

Question 1

An example of a size-independent property is _______.

A. densityB. massC. volumeD. wattage


Answer

The answer is A. A block of wood three times the size of another block of wood does not need to be denser. It must, however, have a greater volume.


Question 2

A tennis ball and a billiard ball may be the same size, but they will definitely NOT have the same _______.

A. densityB. parityC. viscosityD. width


Answer

The answer is A. A billiard ball is denser than a tennis ball.


Question 3

Density is equivalent to mass divided by _______?

The answer is volume. The formula for determining density is D = m/V.

Answer


Question 1

Any change in size, shape, form, or state is known as a _______?

A. chemical changeB. chemical propertyC. physical changeD. physical property


Answer

The answer is C. In physical changes, the identity of the substance in question remains the same throughout.


Question 2

A change from one type of matter to another is known as a _______?

A. chemical changeB. chemical propertyC. physical changeD. physical property


Answer

The answer is A. In a chemical change the identity of the substance itself is altered.


Question 3

Explain the law of the conservation of mass.

The law of the conservation of mass says that the total mass will be the same before and after a chemical or physical change. Mass cannot disappear, and no mass is created.

Answer

Section 2.2: Atoms are the Fundamental Components of Elements

• Chemists know of elements from atomic numbers 1 (hydrogen) to 118 (ununoctium) have been discovered or reportedly synthesized, with elements 113, 115, 117 and 118 having yet to be confirmed. The first 98 elements exist naturally although some are found only in trace amounts and were initially discovered by synthesis in laboratories. Elements with atomic numbers from 99 to 118 have only been synthesized, or claimed to be so, in laboratories.

• These few 98 that are found in nature combine in different ways to form all the substances in the universe.

• Element – any material consisting of only one type of atom, ie: pure gold, nitrogen, carbon

• Periodic table – all these elements are listed in the periodic table .

• Each element is designated by its atomic symbol, ie: C for carbon, Cl for chlorine, Au for gold (after its Latin name aurum), Pb for lead (Latin name plumbum)


• Naming elements and compounds has conventions.

• Elemental formula – how many elements are bound together.– Individual atoms – Au and Li– 2 or more atoms bonded into molecules in their

natural state – N2, O2, S8


• Compound – when atoms of different elements bond to one another, ie: – Sodium and chlorine → sodium chloride– Nitrogen and hydrogen → ammonia

• Chemical formula – a compound is represented using symbols for the elements. They are written together– sodium chloride → NaCl

– Ammonia → NH3

Section 2.3: Atoms can combine to Form Compounds

• The chemical formula for the compound sodium chloride tell us that there is 1 sodium atom for every one chlorine atom. – sodium chloride → NaCl

• The chemical formula for the compound ammonia tells us that there one nitrogen atom for every 3 hydrogen atoms.– Ammonia → NH3


• Compounds have different physical and chemical properties than their elemental components.– sodium chloride → NaCl

• Sodium – cut easily with knife, soft, silvery, metal. M.p. is 97.5ᵒC, reacts violently w/ water

• Chlorine – yellow-green gas, toxic, used a chemical warfare agent in WWI

• NaCl – translucent, brittle, colorless crystal, not toxic, essential to living organisms, salty


• Compounds are named according to the elements they contain.

• International Union for Pure and Applied Chemistry (IUPAC) developed naming system which is very intricate.

• Three guidelines that are important in naming most simple compounds consisting of 2 elements and many other more complex compounds.


• Guideline 1 – The name of the element farther to the L in the P.T. is followed by the name of the element farther to the R, with the suffix –ide added to the end.

NaCl – Sodium chloride

HCl – Hydrogen chloride

Li2O – Lithium oxide

CaF2 – Calcium fluoride

MgO – Magnesium oxide

Sr3P2 – Strontium phosphide


• Guideline 2 – When 2 or more non-metal compounds have different numbers of the same elements, prefixes are added to remove ambiguity.– One – mono CO – Carbon monoxide– Two – di CO2 – Carbon dioxide– Three – tri SO3 – Sulfur trioxide– Four – tetra N2O4 – Dinitrogen tetroxide– Five – penta PCl5 – Phosphorous pentachloride


• Guideline 3 – Many compounds are referred to by common names, not their systematic names.

– Water – dihydrogen oxide

– Ammonia – Trihydrogen nitride

– Methane – Tetrahydridocarbon

– Pteroenone – 5(S)-methyl-6(R)-hydroxy-7,9-dimethyl-7,9-diene-4-undecanone


• Most materials are mixtures of: elements, compounds or both.

– Stainless steel – iron, chromium, nickel, carbon

– Seltzer water – water, carbon dioxide

– Earth’s atmosphere – nitrogen, oxygen, argon, carbon dioxide, water vapor

– Tap water – compounds of water, calcium, magnesium, fluorine, iron, potassium, chlorine, sulfur, lead, mercury, cadmium, dissolved oxygen, nitrogen, carbon dioxide

Section 2.4: Most materials are Mixtures

Separating Mixtures• Some can be separated easily by physical

means: rocks and marbles, iron filings and sulfur (use magnet)

• Distillation - differences in physical properties can be used to separate mixtures – m.p. & b.p.

• Filtration - separates a solid from the liquid in a heterogeneous mixture (by size) – filter paper


Distillation: takes advantage of different boiling points.

NaCl boils at 1415 oC


Components of dyes such as ink may be separated by paper chromatography.


• Pure – single element – pure gold• Impure – mixture with two or more elements

or compounds– Heterogeneous – the mixture is not uniform in

composition• Chocolate chip cookie, gravel, soil.

– Homogeneous - same composition throughout; called “solutions”

• Kool-aid, air, salt water

• Every part keeps it’s own properties.

Section 2.5: Chemists Classify Matter as Pure or Impure

• Solutions and suspensions are homogeneous mixtures– Solution – all components in same (single) phase –

air, salt water, white gold– Suspension – different components are in different

(2 or more phases) phases such as solids in liquids, liquids in gases, etc. – milk, blood, clouds

• Spin in a centrifuge to distinguish between solutions and suspensions.

Section 2.5: Chemists Classify Matter as Pure or Impure

Compound vs. Mixture

Compound Mixture

Made of one kindof material

Made of more thanone kind of material

Made by a chemical change

Made by a physical change

Definitecomposition

Variablecomposition

Elements vs. Compounds

• Compounds can be broken down into simpler substances by chemical means, but elements cannot.

• A “chemical change” is a change that produces matter with a different composition than the original matter.

• Elements organized in periodic table based on physical and chemical properties.

• Metals – most of known elements– Shiny– Opaque– Good conductors of electricity and heat– Malleable– Ductile (drawn into wires)– Most are solids at room temperature

• Nonmetals• Metalloids• Gases

Section 2.6: Elements are Organized in the Periodic Table by their Properties


• Nonmetals – on right side of PT (except H)– Brittle– Shatter when hammered– Transparent– Poor conductors of electricity and heat– Not malleable– Not ductile (drawn into wires)– At room temperature may be solid, liquid or gas

• Nonmetals• Metalloids• Gases



• Metalloids – 6 elements (B, Si, Ge, As, Sn, Sb)– Between metals and nonmetals on PT– Properties of both metals and nonmetals– Weak conductors of electricity and heat (good

semiconductors for integrated circuits)– Ge – closer to metallic side so more metallic

properties – integrated circuits with Ge operate faster than those with Si but Si more abundant


• Elements organized in periodic table by horizontal rows and vertical columns

• Row – called a period• Column – called a group• Periodic trends – called periodicity

– Atomic size decreases going L to R


• Columns – properties of elements tend to be similar, grouped in families.– Group 1 - Alkali metals - from Arabic word al-qali, ashes,

ashes mixed with water produce a slippery solution that removes grease

– Group 2 - Alkaline-earth metals – fire-resistant substances known to ancient alchemists as “earth”

– Group 16 – Chalcogens – from Greek “ore-forming”– Group 17 – Halogens – from Greek “salt-forming”– Group 18 – Noble gases – unreactive gases that tend not to

combine with other elements, nobility did not interact with common folk


• Columns – properties of elements tend to be similar, grouped in families.– Groups 3 – 12 – Transition metals – harder than alkali

metals, do not form alkaline solutions with water, less reactive with water

– Inner transition metals – 6th and 7th periods of PT– Sixth period – Lanthanides – fall after lanthanum, tend to

occur mixed together in the same locations in the Earth• Difficult to purify• LEDs

– Seventh period – Actinides – fall after actinium, • Difficult to purify• Uranium and plutonium


Chapter 2: Elements of Chemistry Table of Contents Section 2.1: Matter has Physical and Chemical...

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