atoms, elements, and ions the language of chemistry chemical elements -chemical elements - –pure...

Atoms, Elements, and Ions

The Language of The Language of ChemistryChemistryThe Language of The Language of ChemistryChemistry

• CHEMICAL ELEMENTSCHEMICAL ELEMENTS - - – pure substances that cannot be decomposed by pure substances that cannot be decomposed by

ordinary means to other substances.ordinary means to other substances.

SodiumBromine

Aluminum

Lesson 1The Atom: From Idea to Theory

Essential Question

•How has the theory of the atom evolved over time?

Objectives

•To summarize Dalton’s atomic theory.

•To explain the laws that support Dalton’s atomic theory.

An atom consists of aAn atom consists of a

• nucleusnucleus

– (of (of protonsprotons and and neutronsneutrons) )

• electronselectrons in space about the nucleus. in space about the nucleus.

The The AtomAtom

NucleusNucleus

Electron cloudElectron cloud

The Structure of An Atom

Copper Copper atoms on atoms on silica silica surface.surface.

• An An atomatom is the smallest particle of an is the smallest particle of an element that has the chemical element that has the chemical properties of the element.properties of the element.

Distance across = 1.8 nanometer (1.8 x 10-9 m)

History of the atom

• Not the history of atom, but the idea of the atom.

• Original idea began 1. Ancient Greece (400 B.C.)

»Democritus- Greek philosopher• “father of modern science”

2. India (600B.C.)

1.Hindu Nyaya philosophy

Not really sure which one.

History of Atom

• Looked at beach

• Made of sand

• Cut sand - smaller sand

Smallest possible Smallest possible piece?piece?Atomos - not to be Atomos - not to be cutcut

Another Greek• Aristotle - Famous natural philosopher

• Believer of the 4 earthly elements

– Fire - Hot

– Air - light

– Earth - cool, heavy

– Water – wet

• Plus one of his own

»Aether – divine/heavenly bodies• Blend these elements in different

proportions to get all substances

Who Was Right?

• Greek society was slave based.

• Beneath famous to work with hands.

• Did not experiment.

• Greeks settled disagreements by argument.

• Aristotle was more famous, so he won.

• His ideas carried through middle ages.

• Later, Alchemists attempted to change lead to gold.

Who’s Next?

• Late 1700’s - John Dalton- from England.–Math & natural philosophy tutor- summarized

results of his experiments and those of others.

• Dalton’s Atomic Theory

• Combined ideas of elements with that of atoms.

Dalton’s Atomic Theory

1. matter is composed, indivisible particles (atoms)

2. all atoms of a particular element are identical3. different elements have different atoms4. atoms combine in certain whole-number

ratios 5. Chemical reactions involve the

rearrangement of atoms. No atoms are created, destroyed, or

changed into atoms of any other elements.

Dalton’s support for his theory

• Law of Conservation of Mass – Mass is neither created nor destroyed during ordinary chemical reactions.

• Let’s look at an equation:

• 2H2 + O2 >> 2H2O• The quantity and mass of reactants

equals the quantity and mass of the products.

Problems with Dalton’s Atomic Theory?1. matter is composed, indivisible particles

Atoms Can Be Divided, but only in a nuclear reaction2. all atoms of a particular element are identical

Does not Account for Isotopes (atoms of the same element but a different mass due to a different number of neutrons)!

3. different elements have different atomsYES!

4. atoms combine in certain whole-number ratiosYES! Called the Law of Definite Proportions

5. In a chemical reaction, atoms are merely rearranged to form new compounds; they are not created, destroyed, or changed into atoms of any other elements.Yes, except for nuclear reactions that can change atoms of one element to a different element

Modern Atomic Theory• We know today that atoms are made

of electrons, protons, neutrons.

• We will study that next.

Even More Modern Atomic Theory•Known as the Standard Model•protons & neutrons are made of six different “flavors” of quarks.•Electrons are made of leptons

Plus there’s more• Fermions Baryons

• Neutrinos Gluons

• Higgs-Boson – the most fundamental particle

• Not to mention that EVERY particle of matter has an antimatter counterpart.

• But we are not studying this stuff!

Learning Check 1a

1. C + O2 >> ?? According to the Law of Conservation of Mass, the correct answer for the product is:

A. CO

B. C2O

C. CO2

D. C1/2O

Learning Check 1b• Which of Dalton’s statement(s) is NO longer

correct today?

1.All matter is composed of atoms.

2.Atoms of any given element are identical, and are different than atoms of another element.

3.Atoms cannot be created, destroyed, or subdivided.

4.Atoms of different elements combine in whole number ratios.

5. In chemical reactions, atoms are combined, separated, or rearranged.

Isotopes-atoms of an element with different # neutrons

Nuclear fission – splitting an atom

Learning Check 1c

• Explain how an idea, an opinion, a theory, and a law all become connected?

• First, someone has an idea; then persuades others to believe, which is an opinion. Skeptical people need proof. Experiments and data provide proof which creates a theory. After many, many years of experiments trying to disprove without success, a theory becomes a law.

Lesson 2Structure of the Atom

Essential Question

•How has scientific discovery and technology supported the structure of the atom?

Objectives

•To summarize the experiments that contributed to the structure of the atom.

–Describe the structure of an atom including location of protons, electrons, and neutrons with respect to the nucleus.

–Distinguish among protons, electrons, and neutrons in terms of relative mass and charge.

Parts of Atoms

• J. J. Thomson - English physicist. (1897)

• Made a piece of equipment called a cathode ray tube.

• It is a vacuum tube - all the air has been pumped out.

Thomson’s Experiment

Voltage source

+-

Vacuum tube

Metal Disks


Voltage source

+-

Thomson’s ExperimentThomson’s Experiment

Voltage source

+-

Passing an electric current makes a Passing an electric current makes a beam appear to move from the beam appear to move from the negative to the positive endnegative to the positive end


Voltage source

+-

Voltage source


• By adding an electric field

Voltage source


By adding an electric fieldBy adding an electric field

+

-

Voltage source


By adding an electric field he found By adding an electric field he found that the moving pieces had a that the moving pieces had a negative negative chargecharge

+

-

More from Thomson

• JJ Thomson third experiment confirmed that the negative charge was coming from very tiny particles (1000x smaller than hydrogen atom) and were not rays. He called them electrons.

• In 1904 Thomson proposed his model of an atom.

– Original knickname - Plum Pudding Model

– Today’s knickname – Blueberry Muffin model (Why?)

Millikan’s Experiment (1909)• Millikan determined the size of the charge of

an electron.

• He put a charge on a tiny drop of oil and measured how strong an electric field had to be in order to stop the oil drop from falling.

http://youtu.be/91E6KvCvRf0

Rutherford’s experiment• Ernest Rutherford -English physicist.

(1911)– Believed in Thomson’s model of the atom (1904).

– Wanted to see how big they are.

– Used radioactivity.

– Alpha particles - positively charged pieces- helium atoms minus electrons

– Shot them at gold foil which can be made a few atoms thick.

Rutherford’s experiment

• When an alpha particle hits a fluorescent screen, it glows.

• Here’s what it looked like

Lead block

Uranium

Gold Foil

Fluorescent Screen

He Expected

• The alpha particles to pass through without changing direction very much.

• Because…?

• …the positive charges were thought to be spread out evenly. Alone they were not enough to stop the alpha particles.

What he expected

Because

He thought the mass was evenly distributed in the atom

Since he thought the mass was evenly distributed in the atom

What he got

+

How he explained it

• Atom is mostly empty.

• Small dense, positive piece at center.

• Alpha particles are deflected by it if they get closeenough.

Density & the AtomConclusion

• Since most of the particles went through, it was mostly empty space.

• Because the pieces turned so much, the positive pieces were heavy.

• Small volume, big mass, big density.

• This small dense positive area is the nucleus.

Learning Check 2aSubatomic particles

Electron

Proton

Neutron

Name Symbol Charge

Relative mass

Actual mass (g)

e-

p+

n0

-1

+1

0

0.0055

1

1

9.11 x 10-28

1.67 x 10-24

1.67 x 10-24

Learning Check 2b

Scientist Discovery

Rutherford A. Mass of electrons

Thomson B. Positive charge of nucleus

Millikan C. negative charge of electrons

B

C

A

More on Rutherford• 1911 – he named the center of atom

nucleus, meaning “little nut.”

• Designed a model of the atom

• 1920 – After further experiments Rutherford named the + charged particles in the nucleus – protons.

• He predicted that there was a mass of neutral charge particles in the nucleus, but did not conduct any experiments.

Rutherford Atom Modelno neutrons yet

Discovery of the neutron

• It was known, but not understood, that the A was approximately twice the value of the Z for an element.

• 1932 James Chadwick conducted experiments using radioactive material.

• Discovered a particle in the nucleus with no charge – called it the neutron.

Atomic Theory- Law of Definite Proportions

• Law of Definite Proportions:

–A chemical compound has the same exact proportions by mass regardless of the size of the sample or source of the compound.

–Ex: The composition of pure water H2O is ALWAYS be 11.2% hydrogen and 88.8% for oxygen by mass.

Example 1

Law of Definite Proportions Worksheet

1.Remember your Rules of Significant Figures1. Multiply/Divide – Limiter is the value with least

amount of sig figs.

2. Add/Subtract – Limiter is value with least amount of decimals.

2.When multiplying by 100%, the % sign is the unit of measure. Do not unit % key on calculator.

Example 2• A sample of sodium chloride NaCl

weighing 175.35g contains 60.6% Cl by mass.

1. How many grams of Cl are in the sample?

2. How many grams of Na are in the sample?

Percent Composition WorksheetYou will need a Calculator and a Periodic

Table.

1.For every compound determine how many atoms of each element are present.

2.Find the mass of each element in the compound on the P.T. (Round 2 decimal places)

3.Calculate the sum of the masses of the elements, call this the total mass.

4.Divide the mass of the element by the total mass, then multiply by 100%.

% Composition: Example

Laws Pertaining to Atomic Theory-Law of Multiple Proportions

• Law of Multiple Proportions– Is when 2 elements combine to form more than one

compound. The ratio of the masses of the second element when combined with a certain mass of the first element is ALWAYS a ratio of the small whole numbers.

– Ex:CO vs. CO2. In CO 1.33g oxygen combine with 1g carbon, while in CO2,there are 2.66g of oxygen that combine with 1g carbon.

Lesson 3Counting Atoms

Essential Question

How do you distinguish between an atom, an ion, and an isotope?

Objectives

•To calculate the atomic number, mass number, and average atomic mass.

•To explain what isotopes are.

ELEMENTS THAT EXIST AS ELEMENTS THAT EXIST AS DIATOMICDIATOMIC MOLECULES MOLECULES


Remember:

HOFBrINCl

These elements only exist as

PAIRS. Note that when they

combine to make compounds, they

are no longer elements so they are no longer in

pairs!

Hockey Stick and the Puck

ATOM ATOM COMPOSITIONCOMPOSITION

•protons and neutrons in protons and neutrons in the nucleus.the nucleus.

•the number of electrons is equal to the the number of electrons is equal to the number of protons.number of protons.

•electrons in space around the nucleus.electrons in space around the nucleus.

•extremely small. One teaspoon of water has extremely small. One teaspoon of water has 3 times as many atoms as the Atlantic Ocean 3 times as many atoms as the Atlantic Ocean has teaspoons of water.has teaspoons of water.

The atom is mostlyThe atom is mostlyempty spaceempty space

ATOMIC COMPOSITIONATOMIC COMPOSITION• Protons (pProtons (p++))

– + electrical charge+ electrical charge

– mass = 1.672623 x 10mass = 1.672623 x 10-24-24 g g

– relative mass = 1.007 atomic relative mass = 1.007 atomic mass units mass units (amu) (amu) but we can round to 1but we can round to 1

• Electrons (eElectrons (e--))– negative electrical chargenegative electrical charge

– relative mass = 0.0005 amu relative mass = 0.0005 amu but we can round to 0but we can round to 0

• Neutrons (nNeutrons (noo))– no electrical chargeno electrical charge

– mass = 1.009 amu mass = 1.009 amu but we can round to 1but we can round to 1

Atomic Number, ZAtomic Number, Z

All atoms of the same element All atoms of the same element have the same number of have the same number of protons in the nucleus, protons in the nucleus, ZZ

1313

AlAl2727

Atomic numberAtomic number

SymbolSymbolMass NumberMass Number

Mass Number, AMass Number, A• C atom with 6 protons and 6 neutrons C atom with 6 protons and 6 neutrons

is the mass standard is the mass standard • = 12 atomic mass units= 12 atomic mass units• Mass NumberMass Number (A) (A)

= # protons + # neutrons= # protons + # neutrons• This is NOT on the periodic table…(that This is NOT on the periodic table…(that

is the AVERAGE atomic mass)is the AVERAGE atomic mass)• A boron atom hasA boron atom has

A = 5 p + 5 n = 10 amuA = 5 p + 5 n = 10 amu

A

Z

10

5B

A

Z

10

5B

IsotopesIsotopes

• Atoms of the same element (same Z) Atoms of the same element (same Z) but different mass number (A).but different mass number (A).

• Boron-10 (Boron-10 (1010B) has 5 p and 5 nB) has 5 p and 5 n

• Boron-11 (Boron-11 (1111B) has 5 p and 6 nB) has 5 p and 6 n

10B

11B

Figure 3.10: Two isotopes of sodium.

Isotopes Isotopes & Their & Their

UsesUsesBone scans with Bone scans with radioactive radioactive technetium-99. technetium-99.

Isotopes & Their Isotopes & Their UsesUses

The The tritiumtritium content of ground water is content of ground water is used to discover the source of the water, used to discover the source of the water, for example, in municipal water or the for example, in municipal water or the source of the steam from a volcano. source of the steam from a volcano.

Atomic Symbols

Show the name of the element, a hyphen, and

the mass number in hyphen notation

sodium-23

Show the mass number and atomic number

in nuclear symbol formmass number 23 Na

atomic number 11

Isotopes?

Which of the following represent isotopes of the same element? Which element?

234 X 234

X235

X238

X

92 93 92 92

Counting Protons, Neutrons, and Electrons

• Protons: Atomic Number (from periodic table)• Neutrons: Mass Number minus the number of protons

(mass number is protons and neutrons because the mass of electrons is negligible)

• Electrons: – If it’s an atom, the protons and electrons must be

the SAME so that it is has a net charge of zero (equal numbers of + and -)

– If it does NOT have an equal number of electrons, it is not an atom, it is an ION. For each negative charge, add an extra electron. For each positive charge, subtract an electron (Don’t add a proton!!! That changes the element!)

Learning Check 3a – Counting

Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms.

12C 13C 14C 6 6 6

#p+ _______ _______ _______

#no _______ _______ _______

#e- _______ _______ _______

Learning Check 3b

An atom has 14 protons and 20 neutrons.A. Its atomic number is

1) 14 2) 16 3) 34

B. Its mass number is1) 14 2) 16 3) 34

C. The element is1) Si 2) Ca 3) Se

D. Another isotope of this element is

1) 34X 2) 34X 3) 36X 16 14 14

IONS IONS

• IONSIONS are atoms or groups of atoms with a positive or negative are atoms or groups of atoms with a positive or negative

charge. charge.

• Taking awayTaking away an electron from an atom gives a an electron from an atom gives a CATIONCATION with a with a

positive chargepositive charge

• AddingAdding an electron to an atom gives an an electron to an atom gives an ANIONANION with a with a

negative chargenegative charge..

• To tell the difference between an atom and an ion, look to see if To tell the difference between an atom and an ion, look to see if

there is a charge in the superscript! Examples: Nathere is a charge in the superscript! Examples: Na++ Ca Ca+2+2 I I-- O O-2-2

Na Ca I ONa Ca I O

Forming Cations & Forming Cations & AnionsAnions

Forming Cations & Forming Cations & AnionsAnions

A A CATIONCATION forms forms when an when an atom atom losesloses one or one or more electrons.more electrons.

An An ANIONANION forms forms when an when an atom atom gainsgains one or one or more electronsmore electrons

Mg --> Mg2+ + 2 e- F + e- --> F-

PREDICTING ION CHARGESPREDICTING ION CHARGESPREDICTING ION CHARGESPREDICTING ION CHARGES

In generalIn general

• metalsmetals (Mg) (Mg) lose electrons lose electrons ---> ---> cationscations

• nonmetalsnonmetals (F) (F) gain electronsgain electrons ---> ---> anionsanions

Charges on Common Charges on Common IonsIons

Charges on Common Charges on Common IonsIons

+3

-4 -1-2-3+1

+2

By losing or gaining e-, atom has same By losing or gaining e-, atom has same number of e-’s as nearest Group 8A atom.number of e-’s as nearest Group 8A atom.

Learning Check 3c – Counting

State the number of protons, neutrons, and electrons in each of these ions.

39 K+ 16O -2 41Ca +2

19 8 20

#p+ ______ ______ _______

#no ______ ______ _______

#e- ______ ______ _______

Learning Check 3d

Write the nuclear symbol form for the following atoms or ions:

A. 8 p+, 8 n, 8 e- ___________

B. 17p+, 20n, 17e- ___________

C. 47p+, 60 n, 46 e- ___________

AVERAGE AVERAGE ATOMIC ATOMIC MASSMASS

• Because of the existence of isotopes, the Because of the existence of isotopes, the mass of a collection of atoms has an average mass of a collection of atoms has an average value.value.

• Boron is 20% Boron is 20% 1010B and 80% B and 80% 1111B. That is, B. That is, 1111B is B is 80 percent abundant on earth. 80 percent abundant on earth.

• For boron atomic weightFor boron atomic weight

= 0.20 (10 amu) + 0.80 (11 amu) = 10.8 amu= 0.20 (10 amu) + 0.80 (11 amu) = 10.8 amu

10B

11B

Isotopes & Average Atomic Isotopes & Average Atomic MassMass

• Because of the existence of isotopes, the mass Because of the existence of isotopes, the mass of a collection of atoms has an average value.of a collection of atoms has an average value.

• 66Li = 7.5% abundant and Li = 7.5% abundant and 77Li = 92.5%Li = 92.5%

–Avg. Atomic mass of Li = ______________Avg. Atomic mass of Li = ______________

• 2828Si = 92.23%, Si = 92.23%, 2929Si = 4.67%, Si = 4.67%, 3030Si = 3.10%Si = 3.10%

–Avg. Atomic mass of Si = ______________Avg. Atomic mass of Si = ______________

Lesson 4Organizing the Periodic Table

Essential Question

How are elements grouped in the Periodic Table?

Objectives

•To identify similar properties of elements in groups and periods.

ElementsElement- atoms having an identical

number of protons in each nucleus. Elements cannot be reduced to simpler substances by normal chemical means.

• Elements are organized into the Periodic Table of Elements by their Atomic Number

•1H 2He 3Li 4Be 5B 6C 7N

The Periodic Table

PeriodsPeriods in the Periodic in the Periodic TableTable

GroupsGroups in the Periodic in the Periodic TableTable

Elements in groups react in similar ways!

Regions of the Periodic Regions of the Periodic TableTable

Group 1A: Alkali MetalsGroup 1A: Alkali MetalsGroup 1A: Alkali MetalsGroup 1A: Alkali Metals

Cutting sodium metalCutting sodium metal

Reaction of potassium + H2O

MagnesiumMagnesium

Magnesium Magnesium oxideoxide

Group 2A: Alkaline Earth MetalsGroup 2A: Alkaline Earth Metals

Group 7A: The Halogens Group 7A: The Halogens (salt makers) (salt makers) F, Cl, Br, I, AtF, Cl, Br, I, At

Group 7A: The Halogens Group 7A: The Halogens (salt makers) (salt makers) F, Cl, Br, I, AtF, Cl, Br, I, At

Group 8A: The Noble Group 8A: The Noble (Inert) Gases(Inert) Gases

He, Ne, Ar, Kr, Xe, RnHe, Ne, Ar, Kr, Xe, Rn

Group 8A: The Noble Group 8A: The Noble (Inert) Gases(Inert) Gases

He, Ne, Ar, Kr, Xe, RnHe, Ne, Ar, Kr, Xe, Rn• Lighter than air

balloons

• “Neon” signs

• Very Unreactive because they have full electron levels

XeOFXeOF44XeOFXeOF44

Transition ElementsTransition ElementsTransition ElementsTransition Elements

Lanthanides and actinidesLanthanides and actinides

Iron in air gives Iron in air gives iron(III) oxideiron(III) oxide



Remember:

BrINClHOF

These elements only exist as

PAIRS. Note that when they

combine to make compounds, they

are no longer elements so they are no longer in

pairs!

Hockey Stick and the Puck

Compounds

• Compounds are…–Substances that are made from atoms of

two or more different elements chemically bonded together.

–Ex: NaCl, CaCO3

Molecules

• Molecules are…–Substances that are made from atoms of

two or more alike or different element chemically bonded together.

–Ex: O2, H2 (diatomics), NaCl

atoms, elements, and ions the language of chemistry chemical elements -chemical elements - –pure...

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