ATOMIC STRUCTURE

1. BECAUSE THE ATOM IS SO SMALL, IT TOOK THOUSANDS OF YEARS TO ESTABLISH EVEN A SIMPLE THEORY AND MANY VERY INDIRECT EXPERIMENTS TO ARRIVE AT TODAY MODEL.

2. EARLY THEORIES THOUGHT MATTER COULD BE DIVIDED INTO SMALLER AND SMALLER PIECES, NEVER ENDING.

3. THE GREEK PHILOSOPHER DEMOCRITUS PROPOSED THAT ALL MATTER WAS MADE OF SMALL UNITS CALLED ATOMS. BUT NOBODY AGREED.

4. THIS THEORY DID NOT BECOME ESTABLISHED UNTIL JOHN DALTON, A SCHOOL TEACHER, SAID ALL MATTER WAS MADE OF ATOMS. HE BASED THIS ON THE THEORY OF THE CONSERVATION OF MATTER ESTABLISHED BY ANTOINE LAVOISIER WHICH STATED THAT, LIKE ENERGY, MATTER CAN NEIGHER BE CREATED OR DESTROYED IN ANY PROCESS. HE ALSO BASED HIS THEORY OF THE ATOM ON THE LAW OF CONSTANT COMPOSITION ESTABLISHED BY LOUIS PROUST. THIS STATES THAT IN A COMPOUND THE ELEMENTS THAT MAKE THEM UP ARE IN CONSTANT PROPORTIONS. FOR EXAMPLE IN WATER H IS ALWAYS 88.9% AND OXYGEN IS ALWAYS 11.1%. BOTH THESE THEORIES INDICATE WHOLE NUMBERS OR ATOMS TO BE SO EXACT.

DALTON STATED THE FOLLOWING:

A. ELEMENTS ARE COMPOSED OF EXTREMELY SMALL PARTICLES CALLED ATOMS.

B. ATOMS ARE NEITHER CREATED OR DESTROYED IN ANY CHEMICAL REACTION.

C. ALL ATOMS FOR THE SAME ELEMENT ARE IDENTICAL, BUT THEY ARE DIFFERENT FOR ANY OTHER ELEMENT.

D. ALL COMPOUNDS ALWAYS HAS THE SAME RELATIVE NUMBERS AND KINDS OF ATOMS. (H2P IS ALWAYS THE SAME.)

C. RUTHERFORD’S MODEL IS USED TODAY AND CONCLUDES THE ATOM IS MADE MOSTLY OF SPACE, WITH A SMALL CONCENTRATED POSITIVE NUCLEUS IN THE CENTER OF THE ATOM, WITH ELECTRONS SPINNING IN ENERGY LEVELS AROUD THE OUTSIDE.

12. RUTHERFORD PORTRAYED THE ATOM AS A MINIATURE SOLAR SYSTEM. WE NOW KNOW THE ELECTRONS DON’T REMAIN IN NICE NEAT ORBITS BUT RATHER MOVE IN AND OUT FROM LEVER TO LEVER. THE MODER MODEL VISUALIZES THE ATOM AS A CLOUD CAUSED BY THE MOTION OF THE ELECTRONS.

13. FURTHER STUDY HAS FOUND ATOMS ARE MADE OF ELECTRONS, PROTONS, AND NEUTRONS. IT HAS ALSO FOUND THESE PARTICLES HAVE SUBPARTICLES OF THEIR OWN. HOWEVER, UNDERSTANDING THIS IS NOT NECESSARY TO UNDERSTAND CHEMISTRY.

14. ATOMIC STRUCTURE:

CHARGE MASS

PROTON + 1 ATOMIC MASS UNIT

NEUTRON 0 1 ATOMIC MASS UNIT

ELECRON - 0 ATOMIC MASS UNIT

15. MOSELY, A STUDENT OF RUTHERFORDS, FINALLY DISCOVERED WHAT MADE ELEMENTS DIFFERENT. HE FOUND EACH ELEMENT HAD A DIFFERENT NUMBER OF POSITIVE CHARGES OR [PROTONS IN ITS NUCLEUS.] THE NUMBER OF PROTONS AN ATOM HAS IS CALLED ITS ATOMIC NUMBER. SINCE ATOMS ARE NEUTRAL, THEY MUST HAVE THE SAME NUMBER OF ELECTRONS (NEGATIVES) AS PROTONS (POSITIVE). THEREFORE, THE ATOMIC NUMBER IS ALSO THE SAME AS THE NUMBER OF ELECTRONS.

ELEMENTS

1. Simplest form of matter.

Made of one type of atom

Can’t be broken down to a simpler form of matter

2. Found on periodic chart

Developed by a Russian Scientist Dmitri Mendeleev.

Represented by a SYMBOL

Single letter C for Carbon

Two letter if Ca for Calcium

Latin Cu for Copper

(Cupric)

3. Elements are made of atoms

Hydrogen

1 electron

Atoms

	1 proton 1 neutron
			Energy Level or cloud

Protons are positive

Neutrons are neutral

Electrons are negative

ELECTRONS ALWAYS ARE THE SAME AS THE NUMBER OF PROTONS

BECAUSE OF THIS AN ATOM IS ALWAYS NEUTUAL

MAXIMUM ELECTRONS PER SHELL

1^ST SHELL 2

2^ND SHELL 8

3^RD SHELL 18

4^TH SHELL 32 (NOTE- WHEN OUTER SHELL THIS NUMBER IS STILL 8)

4. EACH PROGRESSIVE ELEMENT ON THE PERIODIC CHART INCREASES BY ONE PROTON AND ONE ELECTRON.

2

He

4.002602

ATOMIC WEIGHT

NUMBER

ATOMIC MASS

NUMBER

ATOMIC MASS = PROTONS + NEUTRONS 4

ATOMIC = PROTONS 2

NUMBER NEUTRONS 2

THE ATOMIC NUMBER EQUALS PROTONS. IT ALSO EQUALS THE NUMBER OF ELECTRONS, BECAUSE PROTONS AND ELECTRONS ARE ALWAYS EQUAL IN NUMBER. THEREFORE, He HAS 2 ELECTRONS.

16. THE MASS OF AN ATOM IS PRIMARILY THE NUCLEUS WHICH IS MADE UP OF PROTONS AND NEUTRONS. THESE ARE MEASURED BY ATOMIC MASS UNITS. THIS UNIT IS BASED ON CARBON -12.

1 AMU = 1/12^TH OF CARBON = 1.66 x 10^-28

17. THE MASS NUMBER IS THE TOTAL NUMBER OF PROTONS AND NEUTRONS. BY USING THE ATOMIC NUMBER AND MASS NUMBER, TOTAL PROTONS, ELECTRONS AND NEUTRONS CAN BE DETERMINED FOR ANY ELEMENT.

18. USE THE PERIODIC CHART TO FIND THE NUMBER OF PROTONS, ELECTRONS AND NEUTRON IN ANY ELEMENTS.

18 ATOMIC NUMBER

Ar

39.948 ATOMIC MASS

MASS NUMBER = ATOMIC MASS ROUNDED TO THE NEAREST WHOLE NUMBER.

MASS NUMBER = 40 = PROTONS + NEUTRONS

ATOMIC NUMBER = 18 = - PROTONS

22 → NEUTRONS

THE ATOMIC NUMBER IS THE NUMBER OF PROTON. SINCE PROTONS AND

ELECTRONS ARE ALWAYS EQUAL IN NUMBER, THERE IS ALSO 18

ELECTRONS.

EXAMPLE:

54 MASS NUMBER 131

XE AT NUMBER 54

131.29 74 NEUTRONS

54 PROTONS/ELECTRONS

WHY ISN’T THE ATOMIC MASS A WHOLE NUMBER

1. ICONS ARE CHARGED ATOMS. THEY ARE FORMED IN CHEMICAL REACTION WHEN ELEMENTS GIVE UP OR TAKE ON ELECTONS.

EXAMPLE:

11 P 17 P

10e 18e

1P 1e

Na ENDS UP WITH ONE LESS ELECTRON SO IT IS A POSITIVE ION. Cl ENDS UP WITH ONE EXTRA ELECTRON SO IT IS A NEGATIVE ION.

2. ISOTOPES ARE OFTEN CONFUSED WITH IONS. ISOTOPES ARE THE SAME ELEMENT BUT WITH A DIFFERENT NUMBER OF NEUTRONS. ALL ELEMENTS ARE MADE UP OF ISOTOPES.

EXAMPLE: HYDROGEN

NORMAL DEUTERIUM TRITIUM

1 2 3

H H H

1 1 1

1 2 3

-1 -1 -1

0 NEUTRONS 1 NEUTRON 2 NEUTRONS

1 PROTON/ELEC 1 PROTON/ELEC 1 PROTON/ELEC

3. IF AN ATOMS MASS IS MADE OF PROTONS AND NEUTRONS, THE ATOMIC MASS SHOULD BE A WHOLE NUMBER SINCE THERE ARE NO PARTICAL PROTONS OR NEUTRONS.

EXAMPLE: 1 MASS NO = 1

H ATOMIC NO = 1

1 0 NEUTRONS

1 PROTON

1 ELECTRON

WITH THIS ANALYSIS THE ATOMIC MASS SHOULD BE 1.0. HOWEVER, IT IS ACTUALLY 1.0079.

4. THE REASON FOR THIS IS TWO FOLD.

A. AMU ATOMIC MASS UNITS ARE SLIGHTLY DIFFERENT THAN THE WEIGHT OF A NEUTRON AND PROTON.

B. ATOMS ARE TOO SMALL TO WEIGH ALONE. THEREFORE, ATOMS MUST BE WEIGHED IN A GROUP OF ATOMS WITH THE SAME NUMBER OF ATOMS. THIS MEANS YOU ARE WEIGHING A GROUP OF ISOTOPES WITH DIFFERENT WEIGHTS. THIS GIVES AN AVERAGE WEIGHT. THIS CREATES A NUMBER THAT IS NOT EVEN.

EXAMPLE: FIND THE AVERAGE WEIGHT OF THE FOLLOWING THREE NUMBERS:

5LB

4LB

2LB

11LBS

THE AVERAGE IS 11/3 = 3.666LBS. EVEN THOUGH ALL THE WEIGHTS WERE WHOLE NUMBERS, THE AVERGE CONTAINS DECIMALS.

CHEMICAL FORMULAS AND BONDING

1. WHEN ELEMENTS REACT THEY ARE SIMPLY BECOMING MORE STABLE AS A ROCK WOULD AS IT FALLS TO THE GROUND.

2. IN THE CASE OF ATOMS THIS MEANS THEY HAVE 8 ELECTRONS IN THEIR OUTER SHELL. THIS IS KNOWN AS THE OCTET RULE. 2 ELECTRONS IN A CASE OF HELIUM (THIS GIVES THE MAXIMUM LIKE CHARGES WHICH REPEL IN THE CLOSET DISTANCE POSSIBLE TO PROTONS WHICH ATTRACT.)

3. WHEN ELEMENTS REACT WITH EACH OTHER THEY COMBINE SO EACH ELEMENT CAN GET AS CLOSE TO EIGHT IN ITS OUTER SHELL AS POSSIBLE.

4. THE NUMBER OF ELECTRONS IN THE OUTER SHELL CAN BE DETERMINED BY LOOKING AT THE PERIDOIC CHART.

GROUP 1A = 1, IIA = 2, IIIB = 3, IVB = 4ETC.

5. IN THE CASE OF ELEMENTS IN GROUPS IA = IVB, THEY GIVE UP THEIR ELECTRONS TO GET A FULL OUTER SHELL IN THE SHELL BELOW. THE ELEMENTS IN GROUPS VB – VIB WOULD TAKE ON 2 ELECTRONS.

6. WHEN ELEMENTS GIVE UP OR TAKE ON ELECTRONS THEY BECOME CHARGED ATOMS CALLED ICONS. THEREFORE, THEY WILL FORM IONIC BONDS. THIS IS A STATIC ELECTRICAL BOND WHERE THE POSITIVE ION IS ATTRACTED TO THE NEGATIVE ION. THIS BOND FORMS WHEN METALS (ELEMENTS LEFT OF THE DIAGONAL LINE OR CATION) + COMBINE WITH NONMETALS) (ELEMENTS RIGHT OF THE DIAGONAL LINE OR ANION)—

7. IN IONIC COMPOUNDS THE POSITIVE ION IS CALLED A CATION AND THE NEGATIVE ION IS CALLED THE ANION. THIS IS REPRESENTED AS FOLLOWS:

7e^-

1e^-

8. WHEN TWO NONMETALS REACT THEY BOTH NEED TO TAKE ON ELECTRONS TO COMPLETE THEIR EIGHT ELECTRONS IN THE OUTER SHELL. THIS MEANS NEITHER ELEMENT WILL GIVE UP AN ELECTRON, SO THEY MUST SHARE. THIS IS REPRESENTED AS FOLLOWS.

7 e 7 e

9. ATOMS COMBINED TOGETHER BY COVALENT BONDS FORM MOLECULES. THIS CAN BE REPRESENTED BY A STRUCTURAL FORMULA. ONE TYPE OF STRUCTRUAL FORMULA IS A LEWIS STRUCTURE WHERE THE VALENCE ELECTRONS (OTHER SHELL ELECTRONS) ARE REPRESENTED AS DOTS. IN THIS PROCESS EACH ELEMENT NORMALLY ENDS UP WITH 8 DOTS AROUND IT OR ONE LINE WHICH REPRESENTS TWO DOTS.

HOW TO FIGURE OUT LEWIS STRUCTURES

1. SINGLE ELECTROS NORMALLY FORM BOND SITES. IF ONE BOND FORMS THERE WAS ONE SINGLE ELECTRON. IF THERE IS TWO BONDS THERE ARE TWO SINGLE ELECTRONS ETC. (LATER YOU WILL SEE SOME EXCEPTIONS).

2. LOOK ON THE PERIODIC CHART AND SEE WHICH GROUP THE ELEMENT IS IN. USING THE OCTET RULE DECIDE HOW MANY ELECTRONS ARE GIVEN UP OR TAKEN ON TO REACH EIGHT. HOWEVER, MANY THAT WILL BE THE NUMBER OF SINGLE ELECTRONS.

GROUP	TOTAL ELECTRONS	GIVE UP	TAKE ON	SINGLE	BOND SINGLE ELECTRON	FORMED BY VALENCE
I	1	1		1		+1
II	2	2		2		+2
III	3	3		3		+3
IV	4	4		4		+4
V	5		3	3		-3
VI	6		2	2		-2
VII	7		1	1		-1
VII	8	0	0	0		0

FOR EXAMPLE:

IN ADDITION ELEMENTSCAN FORM DOUBLE OR TRIPLE BONDS TO OBTAIN THE OCTET RULE.

H—C=O OR H-C = C-H

10. SOME ELEMENTS ARE EXCEPTIONS TO THE OCTET RULE.

FOR EXAMPLE:

N = O

11. A PERFECTLY COVALENT COMPOUND WITH EQUAL ATTRACTION FOR ELECTRONS BY ALL ELEMENTS HAS NO CHARGE ON THE MOLECULE. THIS IS EXPECIALLY TRUE WITH SUCH THINGS AS Cl₂ OR O₂. HOWEVER, MOST NONMETALS HAVE DIFFERENT ELECTRONEGATIVITIES (A MEASURE OF AN ATOMS ATTRACTIONI FOR ELECTRONS). SINCE NONMETAL ATOMS DO NOT ATTRACT WITH EQUAL FORCE, IT IS POSSIBLE TO FORM A MOLECULE WITHOUT A COMPLETE EQUAL DISTRIBUTION OF ELECTRONS THIS LEADS TO A POLAR MOLECULE (NOT AN ION) WITH PRATIAL CHARGES ON IT. THIS IS REPRESENTED AS FOLLOWS:

5+ 5+

H H

O

5-

12. THIS MEANS THERE IS A CONTINUEM GOING FROM IONIC TO VERY POLAR COVALENT TO LESS POLAR COVALENT TO NON-POLAR COVALENT.

3. IN THE SODIUM ION, THERE IS ONE VALENCE SHELL ELECTRON. THIS LEWIS STRUCTURE IS PICTURED AS FOLLOWS:

Na ·

THIS ELECTRON IS CALLED A SINGLE ELECTRON.

IN NITROGEN THE ELECTRONIC LEWIS STRUCTURE IS AS FOLLOWS:

THE SINGLE ELECTRONS PAIR WITH ELECTRONS FROM OTHER ELEMENTS TO FORM A MOLECULE.

THE TWO PAIRED ELECTRONS ARE CALLED AN UNSHARED PAIR OF ELECTRONS. THE UNSHARED PAIR NORMALLY IS LAST TO GET INVOLVED IN BONDING.

WHEN NITROGEN COMBINES WITH HYDROGEN, THE LEWIS STRUCTURE IS AS FOLLOWS.

••

H•• N ••H

••

H

THE ELECTRONS BETWEEN THE HYDROGEN AND NITROGEN ARE CALLED SHARED PAIRS OF ELECTRONS.

4. IN LEWIS STRUCTURES THE NONMETAL IS THE CENTRAL ELEMENT AROUND WHICH THE MOLECULE IS BUILT. IF THERE ARE JUST NONMETALS THE NONMETAL WITH THE MOST SINGLE ELECTRONS TO BOND WITH IS THE CENTRAL ELEMENT IN THE MOLECULE.

5. WHEN IONIC BONDS ARE FORMED THE METAL IS FIRST AND THE ELECTRONS ARE EXCHANGED AND GIVEN TO THE NONMETAL.

EXAMPLE: Mg •• + FORMS Mg+2 -2

BOND DISTANCE

1. AS YOU GO DONW THE PERIODIC CHART THE ELEMENTS GET LARGER, BECAUSE THE DISTANCE FROM THE NUCLEUS GETS LARGER THERE IS LESS ATTRACTION FOR BONDING ELECTRONS. BECAUSE OF THIS, BOND LENGTHS GET LONGER AS YOU GO DOWN THE CHART.

2. MULTIPLE BONDS CREATE A GREATER ATTRACTION BETWEEN THE BOND ELECTRONS AND THE NUCLEUS MAKING THE BOND LENGTHS SHORTER.

POLARITY

1. POLARITY OF A MOLECULE IS DETERMINED BY TWO THINGS.

A. THE DIFFERENCE OF ELECTRONEGATIVITY OF THE ELEMENTS IN THE MOLECULE LEADING TO THE BOND POLARITY AND A DIPOLAR (POSITIVE AND NEGATIVE POLED) MOLECULE.

B. THE SHAPE OF THE MOLECULE. IF THE NEGATIVE POLES ARE EQUAL IN OPPOSITE DIRECTIONS THE MOLECULE BECOMES NONPOLAR.

CHARACTERISTICS OF IONIC, NONPOLAR COVALENT AND

POLAR COVALENT BONDS

1. IONIC COMPOUNDS HAVE LARGE OPPOSITE CHARGES BETWEEN THE POSITIVE AND NEGATIVE IONS. BECAUSE OF THIS, IONIC COMPOUNDS FROM SOLID LATTICES WHICH ARE BRITTLE.

2. BECAUSE OF THE STRONG CHARGES WITHIN THE MOLECULE THERE IS ALSO STRONG BONDS BETWEEN THE NEGATIVE OF ONE MOLECULE WITH THE POSITIVE OF THE MOLECULE NEXT TO IT. IT IS THE BOND BETWEEN MOLECULES THAT IS BROKEN WHEN MELTING AND BOILING OCCURS (BROKEN BONDS WITHIN THE MOLECULE WOULD CHEMICALLY CHANGE THE SUBSTANCE). BECAUSE THIS BOND IS SO STRONG IONIC COMPOUNDS HAVE HIGH MELTING POINTS AND BOILING POINTS.

3. WHEN IONIC SOLIDS ARE PLACED IN WATER THERE IS ENERGY GAINED FROM THE WATER DISSOLVING THE IONIC SOLIDS. THIS ENERGY COME FROM BONDS BEING FORMED WITH THE IONIC SOLID AND WATER MOLECULES. THIS ENERGY BREAKS THE SOLID LATTICE DOWN AND THE IONS ARE SET FREE IN SOLUTION. WHEN THIS HAPPENS THEY CAN CONDUCT ELECTRICITY.

4. NONPOLAR COVALENT COMPOUNDS HAVE NO OPPOSTIE CHARGE HOLDING THEM TOGETHER. ALL THEY HAVE IS THE ATTRACTION OF THE SHARED ELECTRONS IN THE THE OPPOSITE CHARGED NUCLEI OF THE ATOMS. BECAUSE THERE IS NO CHARGES ON THE NONPOLAR COVALENT COMPOUND THERE IS VERY LITTLE ATTRACTION OR BONDING BETWEEN MOLECULES. SINCE THESE ARE THE GONDS BROKEN IN MELTING AND BOILING, NONPOLAR COVALENT COMPOUNDS HEAT VERY LOW MELTING AND BOILING POINTS. THEREFORE, THEY ARE NORTALLY LIQUIDS OR GASES.

5. NONPOLAR COVALENT COMPOUNDS HAVE A SHIFTING OF ELECTRONS AND CAN FORM AN IMBALANCE OF ELECTRONS IN THE MOLECULE. THIS FORMS A MOMENTARY NEGATIVE AND POSITIVE PORTION OF THE MOLECULE. THIS PATTERN MOMENTARILY GOES THROUGHOUT THE SUBSTANCE FORMING WEAK BONDS CALLED VAN DER WAAL FORCES. THESE ARE THE PRIMARY BONDS BETWEEN MOLECULES OF NONPOLAR COMPOUNDS.

6. POLAR COVALENT COMPOUNDS DO NOT HAVE FULL OPPOSITE CHARGES WITHIN THEIR MOLECULES. THEY DO HAVE PARTICAL CHARGES WHICH CREATE ATTRACTION BETWEEN MOLECULES. THESE BONDS BETWEEN MOLECULES GIVE MODERATE MELTING AND BOILING POINTS BETWEEN IONIC AND NON POLAR COVALENT COMPOUNDS.

7. BECAUSE IONS COMBOUNDS AND POLAR COVALENT COMPOUNDS BOTH HAVE CHARGES, THEY ARE COMPATIVLE WITH EACH OTHER AND ONE WILL DISSOLVE IN THE OTHER. NONPOLAR COMPOUNDS DO NOT HAVE CHARGES AND ARE NOT COMPATIVLE WITH IONIC OR POLAR COLVALENT COMPOUNDS.

NONPOLAR COMPOUNDS ARE COMPATIVLE WITH OTHER NONPOLAR COMPOUNDS AND ONE WILL DISSOLVE IN THE OTHER.

SOAP

1. SOAP IS A LONG ORGANIC COMPOUND (NONMETALS MAKING IT NONPOLAR) WITH SODIUM ON ONE END (SODIUM IS A METAL) THIS MAKES ONE END OF SOAP POLAR. DIRT IS ORGANIC (NONPOLAR). THEREFORE, DIRT DISSOLVES IN SOAP WHILE IT WON’T DISSOLVE IN POLAR COVALENT WATER. HOWEVER, THE SODIUM POLAR END OF SOAP DISSOLVES IN WATER AND THE SOAP WILL CARRY THE DIRT AWAY WITH IT. NOW YOU KNOW HOW SOAP WORKS.