ch 2

CHAPTER 2CHAPTER 2

WARM UPWARM UP

&&

LEARN THE LINGOLEARN THE LINGO

ADDITIONAL RESOURCESADDITIONAL RESOURCES

AtomAtom

Isaac AsimovIsaac Asimov

ISBN:0613033884 ISBN:0613033884

Any chemistry by Asimov is goodAny chemistry by Asimov is good

WARNINGWARNING

The material from this point on may The material from this point on may start out sounding like high school start out sounding like high school chemistrychemistry

The high school sounding material is The high school sounding material is like a runway, we use it to take off like a runway, we use it to take off fromfrom

Don’t get board or over-confident Don’t get board or over-confident with the runway, or you WILL miss with the runway, or you WILL miss the flightthe flight

ATOMIC THEORYATOMIC THEORY

Has been around for over 2,000 years, Has been around for over 2,000 years, the word ATOM is from the Greek word the word ATOM is from the Greek word atomosatomos meaning uncuttable meaning uncuttable

In the early 1800s, atomic theory was In the early 1800s, atomic theory was dusted off and formed the basis of dusted off and formed the basis of modern chemistrymodern chemistry

From here forward, we are talking about From here forward, we are talking about the 1800s flavor of atomic theorythe 1800s flavor of atomic theory

ATOMIC THEORYATOMIC THEORYFour “postulates” (rules):Four “postulates” (rules):

1.1. Each element is composed of very small Each element is composed of very small particles called atomsparticles called atoms

2.2. Atoms of a given element are identical to Atoms of a given element are identical to each other in mass and properties, but each other in mass and properties, but are different from atoms of other are different from atoms of other elementselements

3.3. Atoms of one element can not be Atoms of one element can not be changed into atoms of a different changed into atoms of a different elementelement

4.4. Compounds are formed when atoms of Compounds are formed when atoms of two or more elements combinetwo or more elements combine

ATOMIC THEORYATOMIC THEORY

Explained two laws:Explained two laws:1.1. Constant Composition – Compounds Constant Composition – Compounds

always have the same ratio of always have the same ratio of elementselements

2.2. Conservation of Matter – The total Conservation of Matter – The total mass of material mass of material afterafter a a chemical chemical reactionreaction is the same as the total mass is the same as the total mass beforebefore the reaction (this is the basis for the reaction (this is the basis for everything that will follow in this class)everything that will follow in this class)

ATOMIC THEORYATOMIC THEORYA new law was discovered at this time, A new law was discovered at this time,

the Law of Multiple Proportions:the Law of Multiple Proportions:

If two elements A and B combine to If two elements A and B combine to form more the one compounds, the form more the one compounds, the ratio A to B will be different for each ratio A to B will be different for each compound.compound.

NONO22, NO, NO3 3 (NOx, they cause smog)(NOx, they cause smog)

SOSO22, SO, SO3 3 (SOx,(SOx, they cause acid rain)they cause acid rain)

ATOMIC STRUCTUREATOMIC STRUCTURE

Please forget the “Pool Ball” “Planets Please forget the “Pool Ball” “Planets Around the Sun” image of electronsAround the Sun” image of electrons

Electrons act very strangely Electrons act very strangely For accounting purposes, if we need For accounting purposes, if we need

to, electrons will be drawn as dots or to, electrons will be drawn as dots or minus signs next to the atomic minus signs next to the atomic symbol symbol

ATOMIC STRUCTUREATOMIC STRUCTURE

Read the text book if you want a Read the text book if you want a pitch – by – pitch description of who pitch – by – pitch description of who did what when (this is chemistry, not did what when (this is chemistry, not history)history)

Atoms have two regions – the Atoms have two regions – the nucleus and the electron cloudnucleus and the electron cloud

If this dot If this dot ●● were a nucleus, the were a nucleus, the electron cloud would be on the third electron cloud would be on the third floorfloor

ATOMIC STRUCTUREATOMIC STRUCTURETHE NUCLEUSTHE NUCLEUS

Two particles in the nucleus:Two particles in the nucleus:

ProtonsProtons

NeutronsNeutrons


ProtonsProtons Have an atomic mass of just Have an atomic mass of just

under 1under 1 Have a charge of +1Have a charge of +1 Do not participate in chemical Do not participate in chemical

reactionsreactions Determine what element the Determine what element the

atom isatom is


ProtonsProtons 1 proton is Hydrogen1 proton is Hydrogen 8 protons Oxygen8 protons Oxygen 92 protons is Uranium92 protons is Uranium

ProtonsProtons

We call the NUMBER of We call the NUMBER of protons in an atom the protons in an atom the ATOMIC NUMBER since it ATOMIC NUMBER since it determines what element determines what element it isit is


NeutronsNeutrons Have an atomic mass of 1Have an atomic mass of 1 Have a charge of 0Have a charge of 0 Do not participate in chemical Do not participate in chemical

reactionsreactions Atoms of the same element can Atoms of the same element can

have DIFFERENT numbers of have DIFFERENT numbers of neutronsneutrons


NeutronsNeutrons Atoms of the same element with Atoms of the same element with

different numbers of neutrons are different numbers of neutrons are call isotopescall isotopes

Isotopes of an element have different Isotopes of an element have different weights, but they have identical weights, but they have identical chemical properties (which is why it’s chemical properties (which is why it’s so hard to separate them)so hard to separate them)


If an atom of carbon (atomic number If an atom of carbon (atomic number 6) has 12 neutrons what is it’s atomic 6) has 12 neutrons what is it’s atomic weight?weight?

6 protons (weight ≈1)6 protons (weight ≈1)12 neutrons12 neutrons (weight = 1) (weight = 1) 18 AMUs (Atomic Mass Units)18 AMUs (Atomic Mass Units)

Carbon has an isotope with 14 neutrons Carbon has an isotope with 14 neutrons it’s weight is 20 AMUsit’s weight is 20 AMUs

1 AMU = 1.66054 * 101 AMU = 1.66054 * 10-24-24 grams grams


On the periodic table, carbon weight is On the periodic table, carbon weight is listed as 12.0107, the extra 0.0107 is listed as 12.0107, the extra 0.0107 is from the carbon 14. What fraction of from the carbon 14. What fraction of carbon is C14?carbon is C14?

X*12+y*14 = 12.0107 x+y=1X*12+y*14 = 12.0107 x+y=1

(1-y)12+14y=12.0107 x=1-y(1-y)12+14y=12.0107 x=1-y

12-12y+14y=12.010712-12y+14y=12.0107

2y=0.0107, y=0.0054 or 54 of 10,0002y=0.0107, y=0.0054 or 54 of 10,000


NomenclatureNomenclature To write atomic isotopesTo write atomic isotopes

1.1. Write the atomic symbol Write the atomic symbol CC

2.2. Write the mass number as a Write the mass number as a superscript to the LEFT of the symbol superscript to the LEFT of the symbol 1212CC or or 1414CC

3.3. There is no need to write the atomic There is no need to write the atomic number since it is constant for the number since it is constant for the element (carbon is 6)element (carbon is 6)


Don’t think of electrons as moons Don’t think of electrons as moons orbiting a planetorbiting a planet

Think of them as making concentric Think of them as making concentric shells around the nucleusshells around the nucleus

ATOMIC STRUCTUREATOMIC STRUCTURETHE ELECTRON CLOUDTHE ELECTRON CLOUD

Electrons are most probably in the Electrons are most probably in the shellshell

Each shell level has a certain number Each shell level has a certain number of electrons it can hold (remember of electrons it can hold (remember this in a few slides when we get to this in a few slides when we get to the periodic table)the periodic table)

How electrons behave in these shells How electrons behave in these shells determine the elements chemical determine the elements chemical and sometimes physical propertiesand sometimes physical properties

ATOMIC STRUCTUREATOMIC STRUCTURETHE ELECTRON CLOUDTHE ELECTRON CLOUD

THE PERIODIC TABLETHE PERIODIC TABLE

Some elements have very similar Some elements have very similar chemical propertieschemical properties

When Nobel listed the elements in When Nobel listed the elements in increasing order of atomic number, increasing order of atomic number, he noticed that the every so often, he noticed that the every so often, he came to a non-reactive gas that he came to a non-reactive gas that was followed by a soft, reactive was followed by a soft, reactive metalmetal

He also noticed that the elements in He also noticed that the elements in between also repeated in a patternbetween also repeated in a pattern

So he arranged the elements with similar So he arranged the elements with similar properties in groups.properties in groups.

He listed the groups as columns going He listed the groups as columns going from light on top to heavy on the bottomfrom light on top to heavy on the bottom

The groups were arranged next to each The groups were arranged next to each other left to right by increasing atomic other left to right by increasing atomic number of the first elementnumber of the first element



Columns are called Columns are called GroupsGroups and have and have similar propertiessimilar properties

Rows are called Rows are called FamiliesFamilies and are and are filling the same “levels” of electron filling the same “levels” of electron shellsshells


Some GroupsSome GroupsAlkaliAlkali RareRare HalogensHalogens

NobelNobel

EarthEarth Gasses Gasses MetalsMetals

How to read the tableHow to read the table

Atomic NumberAtomic NumberAtomic SymbolAtomic SymbolAtomic WeightAtomic Weight

Some fancy tables will also have the Some fancy tables will also have the electron configuration on the bottom.electron configuration on the bottom.


47

Ag107.868

2

MOLECULESMOLECULES

Diatomic MoleculesDiatomic Molecules Are made of two atoms of the same Are made of two atoms of the same

element Oelement O22, H, H22

Remember the name BrINClOHFRemember the name BrINClOHF• Br – BromineBr – Bromine ●I - Iodine●I - Iodine• N – NitrogenN – Nitrogen ●Cl – Chlorine●Cl – Chlorine• O – OxygenO – Oxygen ●H – Hydrogen●H – Hydrogen• F - FluorineF - Fluorine

Formulas - Three Main TypesFormulas - Three Main Types

1.1. Molecular – Types and actual Molecular – Types and actual number of atoms involved (Hnumber of atoms involved (H22O, O, CSCS22, MgCl, MgCl2 2 HH22OO22))

2.2. Empirical – Types and ratio of Empirical – Types and ratio of atoms involved (atoms involved (HOHO))

3.3. Structural – Types, amounts, & how Structural – Types, amounts, & how they are put togetherthey are put together

MOLECULESMOLECULES

Ions & Ionic CompoundsIons & Ionic Compounds All atoms want to have a full outer All atoms want to have a full outer

shell of electrons (either 2, 8, 10 or shell of electrons (either 2, 8, 10 or 14)14)

MOLECULESMOLECULES

Ions & Ionic CompoundsIons & Ionic Compounds On the periodic table, elements on On the periodic table, elements on

the left (metals) loose electrons and the left (metals) loose electrons and become positively charged. They are become positively charged. They are called called CATIONS (Plus cats)CATIONS (Plus cats)

Elements on the right gain electrons Elements on the right gain electrons and become negatively charged. and become negatively charged. They are called They are called ANIONS (minus ANIONS (minus onions)onions)

MOLECULESMOLECULES

Ions & Ionic CompoundsIons & Ionic Compounds ““Opposites attract” Paula Abdul 1986Opposites attract” Paula Abdul 1986 Ionic reactions happen when a metal Ionic reactions happen when a metal

looses electrons with a non-metal. looses electrons with a non-metal. The metal becomes positive, the The metal becomes positive, the

non-metal negative and form the non-metal negative and form the ionic compoundionic compound

Ionic compounds are usually soluble Ionic compounds are usually soluble in waterin water

MOLECULESMOLECULES

Ions & Ionic CompoundsIons & Ionic Compounds

Magnesium ChlorideMagnesium Chloride

MOLECULESMOLECULES

Mg-

Cl

-

-

-

-

-

-

-

-

Cl-

-

-

-

-

-

-

Ions & Ionic CompoundsIons & Ionic CompoundsMagnesium ChlorideMagnesium Chloride

MOLECULESMOLECULES

Mg +2-

Cl-1

-

-

-

-

-

-

-

-

Cl-1-

-

-

-

---

Ions & Ionic Compounds - Magnesium Ions & Ionic Compounds - Magnesium ChlorideChloride

We now have MgWe now have Mg+2+2 and 2Cl and 2Cl-1-1

We started with zero net charge, and We started with zero net charge, and we ended with zero net charge we ended with zero net charge ++2+2(2+2(--1) = 01) = 0

The formula is MgClThe formula is MgCl22

MOLECULESMOLECULES

Cross Method of Empirical FormulasCross Method of Empirical Formulas

MgMg+2+2 ClCl-1-1

MOLECULESMOLECULES

21

Full shells are happy shells!!!!Full shells are happy shells!!!!

Why don’t noble gasses participate Why don’t noble gasses participate in reactions?in reactions?

Anticipating Ionic ChargeAnticipating Ionic Charge Mg formed a +2 ion and is in the Mg formed a +2 ion and is in the

second family from the leftsecond family from the left Cl formed a -1 ion and is in the Cl formed a -1 ion and is in the

second family on the rightsecond family on the right The family all the way on the right The family all the way on the right

are the noble gasses. They are stuck are the noble gasses. They are stuck up and don’t count!up and don’t count!

MOLECULESMOLECULES

Anticipating Ionic ChargeAnticipating Ionic Charge Cations – If not in the center “short Cations – If not in the center “short

rows”, count from the left. That’s the rows”, count from the left. That’s the charge the element will usually formcharge the element will usually form

Anions – Skip the noble gas column Anions – Skip the noble gas column and count to the leftand count to the left

At 4, charges switch At 4, charges switch

MOLECULESMOLECULES

Anticipating Ionic ChargeAnticipating Ionic Charge Elements in the middle (transition Elements in the middle (transition

metals) form cations, but can vary in metals) form cations, but can vary in charge from 1 to 7charge from 1 to 7

MOLECULESMOLECULES

Elements on the immediate right of Elements on the immediate right of the transition metals are called the transition metals are called metalloids and usually do not form metalloids and usually do not form ions.ions.

MOLECULESMOLECULES

Covalent BondsCovalent Bonds Ionic bonds transfer electrons from Ionic bonds transfer electrons from

one atom to another setting up an one atom to another setting up an electrical attractionelectrical attraction

CovalentCovalent bonds occur when two bonds occur when two atoms atoms shareshare electrons electrons

At any given instant the electron At any given instant the electron could be with atom 1 or atom 2could be with atom 1 or atom 2

CovalentCovalent – Cumby a – Cumby a

MOLECULESMOLECULES

Covalent BondsCovalent Bonds Organic molecules use Organic molecules use covalentcovalent bonds bonds Carbon and silicone can both bond with Carbon and silicone can both bond with

itselfitself Chains of carbon atoms make organic Chains of carbon atoms make organic

moleculesmolecules

The magic number is The magic number is 4 4 each carbon each carbon forms 4 covalent bondsforms 4 covalent bonds

MOLECULESMOLECULES

Covalent Bonds – Alkanes – Single C – to- C BondsCovalent Bonds – Alkanes – Single C – to- C Bonds

MOLECULESMOLECULES

methane

ethane

propane

MOLECULESMOLECULES

Covalent Bonds – Alkenes – Double C – Covalent Bonds – Alkenes – Double C – to- C Bondsto- C Bonds

ethene

propene

Organic Molecules & the Covalent Organic Molecules & the Covalent BondBond

One final note – unlike ionic molecules, One final note – unlike ionic molecules, you can not anticipate how many you can not anticipate how many bonds will form just by position on bonds will form just by position on the tablethe table

MOLECULESMOLECULES

QUESTIONSQUESTIONS

ch 2

Documents

nucleus atomic structure

atomic weight

atomic isotopes

atomic symbolc

grams atomic structure

atom of carbon atomic

nucleus protons

s flavor of atomic theory