Chapters 2 & 3Matter & The Atom

III. Matter

• Matter: anything that has mass and occupies space (has volume)

Atomic Nature of Matter

• All matter consists of tiny particles called atoms

• Atoms are the fundamental units of which elements are composed

• You can’t see them without a powerful microscope

• Like you can’t see individual grains of sand on a beach from a distance

Ted-ed Video

States of Matter

• Solid: definite shape and volume, high density, not compressible

• Liquid: shape of container, definite volume, high density, not compressible

States of Matter

• Gas: has shape & volume of container, low density, compressible

• Plasma: like a gas at really high temperature (electrons leave nucleus)

• Matter can change from one state into another

What is Plasma?

What’s a Bose Einstein Condensate?

Review

1. What is matter?

2. Why is a solid a solid?

3. Why is a liquid a liquid?

4. Why is a gas a gas?

5. What is plasma?

4 Square Question

•What determines whether an element is a solid, liquid, gas or plasma?

Properties of Matter• Identifying Characteristics

• Physical properties: can be observed without changing the identity of the substance. (Examples: density, color, melting point)

• Chemical properties: cannot be observed without altering the substance. (Examples: flammability, corrosiveness)

Changes in Matter

• Physical change: does not alter identity

• Chemical change: changes identity

• Law of Conservation of Matter:

matter is neither created nor destroyed; it just changes form

Compounds

• Compounds: substances made by bonding two or more elements/atoms in a fixed proportion

• Ex: CO2, H20

• Individual compound particles are often referred to as molecules – atoms “stuck” together

Compound Name Characteristics

Carbon monoxide Poisonous gas

Carbon dioxide Breath out as waste material, plants use it to make sugar

Water Most important liquid on Earth

Hydrogen peroxide Disinfect cuts and bleach hair

Elements and Compounds• Element: substance that cannot be separated

into simpler substances by a chemical change. (listed on the periodic table)

• Elements and compounds are pure substances

• Elements contain one type of atom

• Compounds always contains atoms of different elements in the same composition

• Water is always H20, never HO2

Law of Constant Composition

• A given compound always contains the same proportions by mass of the elements of which it is composed

Types of Mixtures

• Heterogeneous mixture: has visibly different parts

Examples: chocolate chip cookies, concrete, salad dressing

• Homogeneous mixture: do NOT have visibly different parts

Also called “solutions”

Examples: seawater, air, soft drinks

Review1. What is an element? Give an

example.2. What is a compound? Give an

example. 3. What is a mixture? Give an example. 4. Give an example of a heterogeneous

mixture.5. Give an example of a homogenous

mixture.

Think Pair Share Question

• What determines whether something is a mixture or a “pure substance?”

Separating Mixtures

• Filtration: use filter (piece of paper) that catches solid particles but lets liquid through

Separating Mixtures

• Distillation: separates based on boiling points –good for separating liquids from liquids

• Crystallization: evaporate a liquid and a crystal is left behind

FIGURE 2.14: SALT REMAINS AFTER ALL WATER IS BOILED OFF.

Figure 2.14: The solution is boiled and steam is driven off.

Separating Mixtures• Chromatography: mixture flows over a stationary object –

substances in the mixture move at different speeds and separate (dyes)

Figure 2.8:Electrolysis, the decomposition of water by an electric current, is a chemical process.

ELECTROLYSIS

• A method for separating elements in a compound using electricity

Figure 2.18:The organization of matter.

Review

1. How are things separated in distillation?

2. How are things separated in crystallization?

3. How are things separated in chromatography?

4. How are things separated in electrolysis?

4 Square Question

• Think of a substance that you separate by crystallization and one for distillation.

The Elements

• 118 known elements• 94 occur naturally

• 9 of them account for 98% of the total mass of earth’s crust, oceans, and atmosphere

• 4 most common elements in life:

• Carbon, Hydrogen, Oxygen, Nitrogen

• 4 most common elements in the Earth

• Oxygen, silicon, aluminum, iron

HydrogenCesium

Symbols for the Elements

• Element Symbols – symbols that represent the elements.

• Consist of the first one (always capitalized) or two (lowercase) letters of the element’s name

• Sometimes, the symbol is taken from the element’s original Latin or Greek name

Review

1.Define element.

2.Give an example of an element and it’s symbol.

3.Give an example of an element that doesn’t have an “English” symbol.

4.What is the law of constant composition?

Think Pair Share

• Why are symbols used in chemistry? Should all symbols be in a “native tongue” – English in the US, German in Germany, etc.

I. Models of the Atom• Greek philosophers (Democritus) devised a theory of atoms,

or tiny particles

• They couldn’t perform experiments and collect evidence like we do now

• They reasoned and formed conclusions

• They reasoned that if you keep cutting matter in half, you would eventually not be able to cut it anymore

• They called these particles atoms

How Big is an Atom?

• An atom is to an apple as an apple is to the ________?

• The moon

• An atom is to me as I am to the _______.

• The sun

• There are as many atoms in one breath as there are breaths in the ____________.

• Atmosphere Factors of 10 Movie Scale Animation

John Dalton

1. Elements are made up of atoms

2. Atoms cannot be divided into smaller pieces

3. All atoms of a given element are identical

4. Different elements are made of different atoms

5. Compounds always have the same number and kinds of atoms

Dalton Model

Review

1. Who originally came up with the idea of an atom?

2. How big is an atom?

3. Name 3 parts of Dalton’s atomic theory.

William Crookes

• Crookes tested Dalton’s theory using a cathode-ray tube

• Something was traveling from the negative side to the positive side and was being blocked by the cross

J. J. Thomson• Cathode rays – electric current passes through a glass tube

1. negative electrode – cathode

2. positive electrode – anode

Cathode ray is particles with a negative charge (electrons)

J. J. Thomson

• Thomson revised Dalton’s model to include a sphere with a positive charge and negatively charged electrons spread evenly within the positive charge

• Plum pudding model

Robert Millikan – oil drop experiment

• Found charge of an electron

• Calculated the mass of an electron

Review1.What did Crookes

“discover”?

2.What did Thomson do to test Dalton’s hypotheses?

3.What did Thomson’s model of the atom look like?

4.What particle is Thomson given credit for discovering?

5.What did Millikan discover?

Think Pair Share

• Why do teachers make you learn about the history of how something was discovered (like with the atom here)?

Rutherford

• Three types of radiation• Alpha radiation• Beta radiation• Gamma radiation

RADIATION

Figure 3.6: Results of foil experiment if Plum Pudding model had been correct.

Figure 3.5: Rutherford’s experiment.

Earnest Rutherford• Rutherford tested Thomson’s

model in 1906

• When the alpha particles were fired, many bounced off at large angles

• Rutherford said, “It was about as believable as if you had fired a 15-inch shell at a piece of tissue paper, and it came back and hit you.”

• There had a to be a large positive mass somewhere to deflect the alpha particles

• Thus, Thomson’s model could not be correct

Rutherford Experiment: Actual results.

Niels Bohr

• First to discover that electrons travel in separate orbits around the nucleus and that the number of electrons in the outer orbit determines the properties of an element.

A Nuclear Atomic Model• The idea of a nucleus was

developed• Occupies most of the mass

of the atom

• Has a positive charge

• Most of an atom is empty space occupied by nearly massless electrons

• Electrons orbit the nucleus and the number of electrons equals the number of protons in a stable atom

History of Atomic Theory Crash Course

Review 1. Explain what the following scientists contributed to the atomic model:

1. Crookes2. Thomson3. Bohr4. Rutherford

2. What occupies most of the space of an atom?

Think Pair Share

• What do you think the scientists who discovered something new about the atom thought about the scientists before them? For instance, What did Rutherford think of Dalton?

A New Atomic Model

• It was later proposed that another particle must be in the nucleus

• Later called the neutron and discovered to have almost the exact mass of a proton and no charge

The 3 Subatomic Particles

• Nucleus is made up of protons and neutrons• Protons: 1+ charge• Neutrons: no charge

• Both have a similar mass = 1 amu

•Electrons : 1 – charge, very small• mass = 0 amu

Figure 3.9:A nuclear atom viewed in cross section.

Review

1. What are the two particles in the nucleus? What are their charges?

2. What “orbits” the nucleus? What is it’s charge?

3. What unit is used to measure the mass of subatomic particles?

4. How does the mass of the proton compare to the mass of the neutron?

5. How does the mass of the electron compare to the mass of the other two?

Drawing

• Draw and label an atom with all the parts we’ve discusses and their relative locations.

Metals• The majority of elements

are metals (left of staircase)

• Metals have a shiny luster

• Good conductors of heat and electricity

• Solids at room temperature

• Malleable (can be shaped)

• Ductile (can be drawn into wires without breaking)

Nonmetals• Nonmetals are found on the

right side of the periodic table (right of staircase)

• Dull luster

• Poor conductors of heat and electricity

• Many are gases at room temperature

• Brittle (cannot change shape without breaking)

• 96% of the human body is made up of nonmatals

Metalloids• Metalloids are found

between the metals and nonmetals on the periodic table (border staircase)

• Have characteristics of both metals and nonmetals

• Do not conduct heat and electricity as well as metals

• All are solids at room temperature

Atomic Number

• The atomic number is the top number in the element’s periodic table block

• Tells the number of protons in the nucleus of each atom of an element

• Also the number of electrons in an electronically neutral atom

• The number of protons remains constant in every atom of an element

Mass Number and Atomic Mass

• Mass number is the number of protons plus the number of neutrons (different mass numbers for different isotopes)

• Atomic mass is the average mass of all the isotopes of an element

• The atomic mass is found below the element symbol

• The unit used for atomic mass is the atomic mass unit, or “u”

Calculating Neutrons

• To find the number of neutrons in the MOST COMMON isotope of an atom:

• (mass number) - (atomic number)

• So how many neutrons are in Helium? Sulfur?

Electron Shells• This is simplified method of explaining the

orbits of electrons

• There are “shells” around the nucleus kind of like different orbits around a planet.

• Each shell can hold a different amount of electrons:

• Shell #1 – 2 electrons

• Shell #2 – 8 electrons

• Shell #3 – 18 electrons (or 8 when talking bonding)

• Shell #4 - 32 electrons (or 8)

• Not a realistic explanation of how electrons orbit the nucleus

• If an atom were a golf ball, shell #1 would be 1 km away

Bohr Model

Review1. What is an atomic number? What does it

tell you?

2. What is an atomic mass? What is the mass number?

3. How do you calculate number of neutrons in an atom?

4. What is an electron shell?

5. How many electrons fit in the 1st shell? 2nd?

4 Square Question

• Why do we use simplified models to help us understand atoms instead of “accurate” ones?

Ions• Ions are atoms of the same

element that have different numbers of electrons & have a charge

• Except for the elements in Group 18, all atoms have an empty spot in their outermost electron orbital and “nature” hates this

• So atoms either lose or gain electrons to fill these spots

Ions

Isotopes• Isotopes are atoms of the same element

that have different numbers of neutrons

Figure 3.10:Two isotopes of sodium.

Review1. What is an ion? How is it

formed?

2. What type of ion is formed from the elements in group 1? Group 2? Group 7/17? Group 8/18?

3. What is an isotope? How is it formed?

Think Pair Share

• Why is it significant that atoms form ions and isotopes?

The Periodic Table

• The Periodic Table is a chart that organizes and displays information about the elements

• The elements represented by the symbols on the periodic table are placed purposely in their position on the table

• Even the shape of the periodic table is that way on purposePeriodic Table of

Videos

The Periodic Table

• The rows are called periods• They have the same number of energy levels

(1 in the 1s, etc.)

• The columns are called groups• They have similar properties and tend to form

similar bonds

Trends in the periodic table

Elements in the same group

(column) tend to react very similarly

• Ex: Elements H, Li, Na, K, Rb,

Cs, & Fr all react similarly (that’s

why they’re in Group I)

Noble Elements• Appear in nature in the

uncombined state

• Noble Metals – metals that are found in their “pure form”

• Gold, Silver, Platinum, etc.

• Noble Gasses – don’t combine with any other gasses

• Group 18 on the wall

• Generally don’t react with anything

Diatomic Molecules• Some elements never

exist in nature as a single atom

• Diatomic molecules contain two atoms

• I wrote in a “2” by all of them up on the periodic table on the wall

States of MATTER & Allotropes• Solids – in black on the periodic table

• Liquids – blue on the periodic table

• Gases – red on the periodic table

• Allotropes – different forms of a given metal

• Carbon is an example

• Carbon can exist as diamond, graphite, or Buckminsterfullerene

Review1. What is something the shape of the

periodic table can tell you?

2. What are the rows on the periodic table called?

3. What are the columns on the periodic table called?

4. Give 2 traits of metals.

5. Give 2 traits of nonmetals.

6. Give 2 traits of metalloids.

4 Square Question

• Give 2 things we can easily recognize because of the shape of the periodic table?

Origin of Matter• According to the Big Bang theory, the

universe began about twelve to fifteen billion years ago in a violent explosion

• About 3 seconds after the Big Bang, nucleosynthesis set in with protons and neutrons beginning to form the nuclei of simple elements, predominantly hydrogen and helium,

• Yet for the first 100,000 years after the initial hot explosion radiation (light, X rays, and radio waves) dominated the early universe

Origin of Matter• Inside the core of a star, nuclear fusion can create

heavier elements up to Iron (element #26)

• Once a star has “lived it’s life,” the iron core heats up and condenses even more until it “explodes”

• This explosion can create heavier elements

Distribution of the Elements

Dark Matter

•Dark Matter

Review

1. When did the “Big Bang” occur?

2. What is nucleosynthesis?

3. Which two elements formed earliest?

4. Where does nuclear fusion take place in the universe?

5. How are lighter elements formed?

6. How are elements heavier than iron formed?

Think Pair Share

• Trace your atoms back to the Big Bang.