This document provides an overview of atomic structure, quantum theory, and electronic configuration of atoms. It discusses subatomic particles like protons, neutrons, and electrons. It describes Rutherford's experiments that showed atoms are mostly empty space with a small, dense nucleus. The number of protons determines an element, while the number of neutrons can vary between isotopes of the same element. Electrons occupy energy levels outside the nucleus. The document also discusses ion formation and how electron configuration explains how atoms combine to form molecules.
3. SUBATOMIC STRUCTURE
• ALL ATOMS CONSIST OF PROTONS, NEUTRONS
AND ELECTRONS
• PROTONS ARE POSITIVELY CHARGED PARTICLES
THAT RESIDE IN THE NUCLEUS AT THE CENTER
OF THE ATOM
• NEUTRONS ARE PARTICLES WITH NO CHARGE
THAT ALSO ARE CONTAINED IN THE NUCLEUS.
• ELECTRONS ARE NEGATIVELY CHARGED
PARTICLES THAT ARE EXTERNAL TO THE
NUCLEUS.
4. SUBATOMIC STRUCTURE
• The experiments of Ernest Rutherford in the early
1900s, showed that matter consisted of small, highly
concentrated, points of matter (the nucleus) surrounded
by vast areas of empty space (the areas where electrons
exist).
• This is called the “Empty Space Model” of the atom.
• Rutherford shot high energy alpha particles at a gold
foil. The alpha particles acted as “bullets”. Most all the
alpha particles went straight through. A few were
deflected.
• From this experiment, Rutherford concluded that tiny
points of concentrated mass, distributed in mostly
empty space, was the fundamental structure of matter.
5. RUTHERFORD’S EXPERIMENT
(A CLOSE UP)
A FEW
ALPHA
PARTICLES
ARE DEFLECTED
GOLD FOIL
PARTICLES
MOST TRAVEL
STRAIGHT
THROUGH THE
METAL
= NUCLEUS
MOST OF THE ATOM
IS EMPTY SPACE
6. RUTHERFORD’S CONCLUSIONS
MOST OF EVERYTHING IS NOTHING !
IF THE NUCLEUS OF AN ATOM WAS THE
SIZE OF A BASEBALL, THE NEAREST
ELECTRONS WOULD BE MILES AWAY !
WHAT IS INBETWEEN ? EMPTY SPACE !
7. WHAT MAKES ONE ATOM DIFFERENT
FROM ANOTHER ?
• EACH ELEMENT HAS DIFFERING NUMBERS OF
PROTONS. THIS IS WHAT MAKES ELEMENTS
DIFFERENT, THE NUMBER OF PROTONS IT
CONTAINS.
• THE ATOMIC NUMBER OF AN ELEMENT TELLS US
THE NUMBER OF PROTONS IT CONTAINS.
ELEMENTS ON THE PERIODIC TABLE ARE
ARRANGED IN ROWS, LEFT TO RIGHT IN ORDER
OF INCREASING ATOMIC NUMBER. THEY START
WITH HYDROGEN, ATOMIC NUMBER 1,
FOLLOWED BY HELIUM, ATOMIC NUMBER 2,
LITHIUM ATOMIC NUMBER 3, ETC.
8. WHAT ABOUT THE NUMBER OF
NEUTRONS IN AN ATOM ?
• THE NUMBER OF NEUTRONS VARY FROM
ELEMENT TO ELEMENT. SOME ATOMS OF THE
SAME ELEMENT MAY HAVE DIFFERENT
NUMBERS OF NEUTRONS. ATOMS OF THE SAME
ELEMENT WITH DIFFERENT NEUTRON NUMBERS
ARE CALLED ISOTOPES.
• THE MASS NUMBER TELLS US THE COMBINED
NUMBER OF PROTONS AND NEUTRONS IN THE
AVERAGE ATOM (ISOTOPE) OF THAT ELEMENT.
9. DETERMINATION OF ATOMIC MASSES
• Atomic mass is measured in “atomic mass units” (amu).
• By convention (everyone agrees), one amu equals exactly
1/12 of the mass of a carbon 12 atom. Using this unit,
hydrogen 1, the lightest element has an atomic mass of
approximately 1 amu.
• It is important to realize that atomic mass (atomic
weight) and the mass number of an atom are different !
• The mass number equals the number of protons plus
neutrons in an isotope. Atomic mass is the weighted
average of atomic masses in atomic mass units (amu)
based on 1/12 of the mass of carbon 12.
10. CALCULATING THE NUMBER OF
NEUTRONS IN AN ATOM
• THE ATOMIC NUMBER OF THE ELEMENT SODIUM
(Na) IS 11 AND ITS ATOMIC MASS IS 22.99. WE’LL
ROUND THIS NUMBER TO 23. SINCE THE ATOMIC
NUMBER TELLS THE NUMBER OF PROTONS,
SODIUM MUST HAVE 11 PROTONS. THE PROTONS
AND NEUTRONS TOGETHER EQUAL 23. BY
SUBTRACTION, SODIUM MUST HAVE 12 NEUTRONS
IN AN AVERAGE ATOM OF SODIUM.
• WHAT ABOUT AN ATOM LIKE CHLORINE? ITS
ATOMIC MASS IS 35.45. ITS ATOMIC NUMBER IS 17.
IT THEREFORE HAS 17 PROTONS, BUT
SUBTRACTING 17 FROM 35.45 GIVES 18.45. HOW
COULD AN ATOM HAVE .45 NEUTRONS??
11. HAVE YOU FIGURED OUT THE
ANSWER ??
• REMEMBER, THE ATOMIC MASS IS THE AVERAGE OF
THE DIFFERENT ISOTOPES OF THAT ELEMENT. NO ONE
ATOM HAS A MASS OF 35.45. INSTEAD, SOME CHLORINE
ATOMS HAVE MASSES OF 35, SOME 36, SOME 37.
• SO CHLORINE ATOMS OF MASS NUMBER 35 HAVE 18
NEUTRONS, THOSE OF MASS NUMBER 36 HAVE 19
NEUTRONS AND THE MASS NUMBER 37 ATOMS HAVE 20
NEUTRONS.
• THERE IS STILL A QUESTION HOWEVER. THE AVERAGE
OF 35, 36 AND 37 IS NOT 35.45, IT IS 36. WHY ISN’T 36
LISTED AS THE ATOMIC MASS FOR CHLORINE ?
12. WHY NOT A MASS NUMBER OF 36 THEN ?
• IN ORDER TO GET 36 AS AN AVERAGE THERE MUST
BE EQUAL NUMBERS OF ATOMS OF ALL THREE
ISOTOPES OF CHLORINE PRESENT. THIS EQUAL
DISTRIBUTION IS RARELY TRUE FOR ANY
ELEMENT IN NATURE.
• HERE IS ANOTHER EXAMPLE. HYDROGEN ATOMS
OCCUR AS THREE DIFFERENT ISOTOPES,
HYDROGEN WITH AN ATOMIC MASS NUMBER OF 1,
DEUTERIUM, THAT IS HYDROGEN WITH A MASS
NUJMBER OF 2 AND FINALLY TRITIUM, HYDROGEN
WITH A MASS NUMBER OF 3. ON THE PERIODIC
TABLE THE ATOMIC MASS OF HYDROGEN IS
LISTED AS 1.0079, ALMOST 1. CAN YOU EXPLAIN
WHY THE LISTED MASS IS SO CLOSE TO ONE
INSTEAD OF THE ARITHEMATIC AVERAGE OF
TWO?
13. ARITHEMATIC AVERAGES AND WEIGHTED
AVERAGES ARE DIFFERENT. THE ATOMIC
MASS IS A WEIGHTED AVERAGE OF THE
ISOTOPES FOR THAT ELEMENT !
• HYDROGEN 1 (IT HAS 1 PROTON AND NO NEUTRONS)
REPRESENTS 99.985 % OF ALL HYDROGEN ATOMS
• HYDROGEN 2 (IT HAS 1 PROTON AND 1 NEUTRON)
REPRESENTS ONLY 0.015 % OF ALL HYDROGEN ATOMS.
• HYDROGEN 3 (IT HAS 1 PROTON AND 2 NEUTRONS)
REPRESENTS 0.0001 % , ALMOST NO HYDROGEN ATOMS.
• THE WEIGHTED AVERAGE CONSIDERS THAT MOST ALL
HYDROGEN ATOM HAVE A MASS OF 1 AND THEREFORE
THE NUMBER APPEARING ON THE PERIODIC TABLE IS
VERY, VERY CLOSE TO 1.00
14. THE ATOMIC MASS NUMBERS ON THE PERIODIC
TABLE THEN ARE WEIGHTED AVERAGES WHICH
ACCOUNT NOT ONLY FOR THE MASSES OF
DIFFERENT ISOTOPES, BUT ALSO ACCOUNTS FOR
ABUNDANCE (PERCENT) AT WHICH THEY OCCUR IN
NATURE !!
THE AVERAGES WHICH YOU ARE USED TO
WORKING WITH IN MATH CLASS ARE ARITHEMATIC
AVERAGES WHICH DO NOT ACCOUNT FOR
ABUNDANCES.
15. MASSES OF SUBATOMIC PARTICLES
PARTICLE MASS CHARGE
PROTON 1 AMU (1.007277) +1
NEUTRON 1 AMU (1.008665) 0
ELECTRON 1 / 1856 AMU (0.0005486) -1
AMU = ATOMIC MASS UNIT
PROTONS & NEUTRONS ARE VERY MASSIVE AS
COMPARED TO ELECTRONS. MOST ALL OF THE
MASS OF AN ATOM IS IN THE NUCLEUS !
THE MASS OF AN ATOM’S ELECTRONS IS NEGLEGIBLE
(SO SMALL THAT IT DOESN’T COUNT)
16. SO FAR THEN, THE NUMBER OF PROTONS IN THE
NUCLEUS OF AN ATOM EQUALS THE ATOMIC
NUMBER.
THE NUMBER OF NEUTRONS EQUAL THE ATOMIC
MASS MINUS THE ATOMIC NUMBER
• WHAT ABOUT THE NUMBER OF ELECTRONS ??
• WELL, THIS DEPENDS ON WHETHER WE ARE
TALKING ABOUT A NEUTRAL ATOM OR AN ION !
• IN A NEUTRAL ATOM THE NUMBER OF ELECTRONS
AND PROTONS ARE EQUAL, SO THE NUMBER OF
ELECTRONS EQUALS THE ATOMIC NUMBER OF
THAT ATOM.
• IN THE CASE OF IONS THE NUMBER OF ELECTRONS
IS DIFFERENT THAN THE ATOMIC NUMBER.
17. WHAT IS AN ION ?
WHAT ARE THE TWO KINDS OF IONS ?
• IONS ARE ATOMS OR GROUPS OF ATOMS WITH EXTRA
OR MISSING ELECTRONS.
• ATOMS WITH EXTRA ELECTRONS ARE IONS WITH A
NEGATIVE CHARGE AND ARE CALLED ANIONS.
• ATOMS WITH MISSING ELECTRONS ARE IONS WITH A
POSITIVE CHARGE AND ARE CALLED CATIONS. IT IS
IMPORTANT TO UNDERSTAND HERE THAT CATIONS DO
NOT HAVE EXTRA PROTONS, THAT IS THEY DO NOT
AND CAN NOT GAIN PROTONS. IF THEY COULD THEY
WOULD BE COME A DIFFERENT ELEMENT. THE
NUMBER OF PROTONS AN ATOM CONTAINS MAKES THE
ATOM WHAT IS IT !!
18. LET’S DETERMINE THE ATOMIC STRUCTURE
FOR OXYGEN
• OXYGEN IS ELEMENT WITH AN ATOMIC NUMBER
OF 8 AND AN ATOMIC MASS NUMBER OF 16
(OXYGEN OCCURS AS THREE DIFFERENT
ISOTOPES 16, 17 AND 18. SINCE THE ATOMIC
MASS IS SO CLOSE TO 16, MOST ALL OXYGEN
ATOMS (99.8 %) ARE ISOTOPE 16).
• THE MOST COMMON ATOM OF OXYGEN THEN
CONSISTS OF 8 PROTONS AND (16 – 8) OR 8
NEUTRONS IN THE NUCLEUS. IF THE ATOM IS
NEUTRAL IT THEN ALSO CONTAINS 8 ELECTRONS
EXTERNAL TO THE NUCLEUS.
19. WHEN ATOMS COMBINE TO FORM
MOLECULES THE ELECTRONS OF EACH
ATOM MUST FIRST INTERACT.
• HOW ARE THE ELECTRONS ARRANGED IN THE ATOM ?
UNDERSTANDING THIS HELPS US TO DISCOVER HOW
AND WHY ATOMS COMBINE!
• ELECTRON ARRANGEMENTS WITHIN ATOMS ARE
REFERRED TO AS ELECTRON CONFIGURATIONS.
• BEFORE WE CAN UNDERSTAND ELECTRON
CONFIGURATIONS, WE MUST FIRST UNDERSTAND HOW
THEY WERE DISCOVERED IN THE FIRST PLACE. THIS
REQUIRES THE USE OF A SCIENCE CALLED QUANTUM
MECHANICS.
20. BASIC CONCEPTS OF QUANTUM MECHANICS
• ELECTRONS EXIST IN AREAS OUTSIDE THE
NUCLEUS. THESE AREAS ARE CALLED ENERGY
LEVELS. YOU MIGHT HAVE HEARD OF THEM
BEFORE AS “SHELLS” (K, L, M etc.) . THERE ARE
NUMEROUS ENERGY LEVELS AT WHICH THE
ELECTRON CAN BE FOUND, EACH AT A
PROGRESSIVE HIGHER ENERGY.
• THESE LEVELS ARE ASSIGNED NUMBERS 1,2,3,
ETC. AS THE NUMBER INCREASES, THE ENERGY
STATE OF THE ELECTRON BECOMES HIGHER.