Unit 3: Atomic Structure

Chemistry

Outline

PowerPoint Presentation by Mr. John Bergmann

Basics of the Atom

Particle Charge Location inthe Atom Mass

a.m.u.: unit used to measure mass of atoms

proton

neutron

electron

1+

0

1–

in nucleus

in nucleus

orbiting nucleus

~1 a.m.u.

~1 a.m.u.

~0 a.m.u.

atomic number:

--

--

To find net charge on an atom, consider____ and ____.

mass number:

# of p+

the whole numberon Periodic Table determines identity of atom

(# of p+) + (# of n0)

10

Ne20.1797

p+ e–

(It is NOT on “the Table.”)

“When I see a cation, I see a positive ion;

ion:

anion: a (–) ion cation: a (+) ion

-- --

a charged atom

more e– than p+

formed whenatoms gain e–

-- -- more p+ than e–

formed whenatoms lose e–

anions negative ions.areI think that

that is, I… C ion.”A +

19

Description NetCharge

AtomicNumber

MassNumber

IonSymbol

15 p+

16 n0

18 e– 38 p+

50 n0

36 e–

18 e– 1+ 39

Te2– 128

K1+

Sr2+

P3–

88

31153–

38

522–

2+

76 n0

52 p+

54 e–

20 n0

19 p+

protium

Isotopes: different varieties of an element’s atoms

-- -- have diff. #’s of n0; thus, diff. masses

some are radioactive; others aren’t

IsotopeH–1

Mass p+ n0 Common Name

H–2H–3 tritium

deuterium123

1 01 11 2

C–12 atoms C–14 atoms

All atoms of an element react the same, chemically.

6 p+ 6 n0 stable

6 p+ 8 n0 radioactive

a- or b-particles, g rays

Radioactive Isotopes: Nucleus attempts to attain a lower energy state by releasing extra energy as __________.

e.g.,

half-life: the time needed for ½ of a radioactive sample to decay into stable matter

have too many or too few n0

radiation

e.g., C–14: -- half-life is 5,730 years-- decays into stable N–14

Years from now

0

g of N–14present

5,73011,460

1206030157.5

0

Say that a 120 g sample of C-14 is

found today.

g of C–14present

17,19022,920

6090

105112.5

= C–14= N–14

Complete Atomic Designation

I53

125 1–

…gives precise info about an atomic particle

mass #

atomic #

charge (if any)elementsymbol

Goiter due to lack of iodine

iodine is now added to salt

ProtonsComplete

Atomic Designation

92

Neutrons Electrons

34

11

146

45

12

92

36

10

5927

3+Co

3717

1–Cl

55 7+Mn25

23892 U

2311

1+Na

7934

2–Se

20 1817

30 1825

32 2427

Historical Development of the Atomic Model

Greek modelof atom

Greeks (~400 B.C.E.)

Matter is discontinuous (i.e., “grainy”).

Democritus & Leucippus

Hints at the Scientific Atom

** Antoine Lavoisier: law of conservation of mass

** Joseph Proust (1799): law of definite proportions: every compound has a fixed proportion

e.g., water……………………..

chromium (II) oxide…….

8 g O : 1 g H

13 g Cr : 4 g O

Hints at the Scientific Atom (cont.)** John Dalton (1803):

8 g O e.g., water……………………..

chromium (II) oxide…….

hydrogen peroxide..…….

chromium (VI) oxide……

1 g H : 16 g O 1 g H :

13 g Cr 4 g O : 13 g Cr 12 g O :

23

law of multiple proportions: When two different compounds have same two elements, equal mass of one element results in integer multiple of mass of other.

1. Elements are made of indivisible particles called atoms.

2. Atoms of the same element are exactly alike; in particular, they have the same mass.

Isotopes!

John Dalton’s Atomic Theory (1808)

3. Compounds are formed by the joining of atoms of two or more elements in fixed, whole number ratios.

e.g., 1:1, 2:1, 1:3, 2:3, 1:2:1

Dalton’s model

of atom

Atoms are not

indivisible.

NaCl, H2O, NH3, Fe2O3, C6H12O6

** William Crookes (1870s): Rays causing shadow were emitted from cathode.

Maltese cross CRT

radar screen television computer monitor

The Thomsons (~1900)J.J. Thomson discoveredthat “cathode rays” are……deflected by electric and magnetic fields

J.J. Thomson

… (–) particles electrons

+ + + + + +

– – – – – –

electric field lines“cathode rays”

phosphorescentscreen

Crooke’s tube

William Thomson (a.k.a., Lord Kelvin):Since atom was known to beelectrically neutral, he proposedthe plum pudding model.

Lord Kelvin

Thomson’s plum pudding model

-- Equal quantities of (+) and (–) charge distributed uniformly in atom.

-- (+) is ~2000X more massive than (–)

(plumpudding)

+–

+

++

+

+

+ ++

++

–

–

–

– –

–

–– –

–

And now we know of many other subatomic particles:

Chadwick

** James Chadwick discovered neutrons in 1932.

--

-- n0 have no chargeand are hard to detect purpose of n0 = stability of nucleus

quarks,muons,positrons,neutrinos, pions, etc.

photo from liquid H2 bubble chamber

Ernest Rutherford (1909) Gold Leaf Experiment

Beam of a-particles (+) directed at gold leaf surrounded by phosphorescent (ZnS) screen.

a-source

lead block

ZnS screen

goldleaf

particle beam

Most a-particles passed through, some angled slightly, and a tiny fraction bounced back.

Conclusions: 1. Atom is mostly empty space.

(+) particles are concentrated at center. nucleus = “little nut”

(–) particles orbit nucleus.

2.

3.

–

–

–

–

–

–

N

Rutherford’s ModelThomson’s Plum Pudding ModelDalton’s (also the Greek) Model

–+

+

+

+

+

+

+ ++

++–

–

–– –

–

–– –

–

Recent Atomic Models

Max Planck (1900): Proposed thatamounts of energy are quantized

only certain values are allowed

Niels Bohr (1913): e– can possess only certain amounts of energy, andcan therefore be only certain distances from nucleus.

e– foundhere

e– neverfound here

planetary(Bohr) model

N

Biology ExperimentTo conduct a biology experiment, you need 100 mL of cola per trial, and you plan to conduct 500 trials.

If 1 can contains 355 mL of cola, and there are 24 cans in a case, and each case sells for $4.89, and there is 7.75% sales tax…

A. How many cases must you buy?

B. How much will the cola cost?

cases 5.86 cans 24

case 1 mL 355

can 1 mL 50,000 cases X

$31.61385 1.0775 case 1

$4.89 cases 6 $ X

6 cases

$31.61

quantum mechanical modelelectron cloud modelcharge cloud model

Schroedinger, Pauli, Heisenberg, Dirac (up to 1940):According to the QMM, we never know for certain where the e– are in an atom, but the equations of the QMM tell us the probability that we will find an electron at a certain distance from the nucleus.

Average Atomic Mass (Atomic Mass, AAM)This is the weighted average mass of all atoms of an element, measured in a.m.u.

For an element withisotopes A, B, etc.:

AAM = Mass A (% A) + Mass B (% B) + …

(use the decimal form of the %;

e.g., use 0.253 for 25.3%)

% abundance

Ti has five naturally-occurring isotopes

Lithium has two isotopes.Li-6 atoms have mass 6.015 amu;Li-7 atoms have mass 7.016 amu.Li-6 makes up 7.5% of all Li atoms.Find AAM of Li.

AAM = Mass A (% A) + Mass B (% B)

AAM = 6.015 amu (0.075) + 7.016 amu

AAM = 6.94 amu

(0.925)

AAM = 0.451 amu + 6.490 amu

Li batteries

** Decimal number on Table refers to…molar mass (in g) OR AAM (in amu).

6.02 x 1023 atoms 1 “average” atom

Isotope

Si-28

% abundance

27.98 amu 92.23%

Mass

Si-29Si-30

28.98 amu 4.67%

AAM = MA (% A) + MB (% B) + MC (% C)

3.10%?

= 27.98 (0.9223) + 28.98 (0.0467) + X (0.031)28.086

28.086 = 25.806 + 1.353 + 0.031X

28.086 = 27.159 + 0.031X0.927 = 0.031X

0.0310.031X = MSi-30 = 29.90 amu

Electron Configurations “e– Jogging” Rules1. Max. of two e– per jogging track (i.e., orbital).

2. Easier orbitals fill up first. s orbital(level)

p orbital(rolling hills)

d orbital(steep hills)

3. e– must go 100X around. 4. All orbitals of equal difficulty must have one

e– before any doubling up.5. e– on same orbital must go opposite ways.

1s orbital(1 of these, 2 e–)

2s orbital(1 of these, 2 e–)

3s orbital(1 of these, 2 e–)

4s orbital(1 of these, 2 e–)

2p orbitals(3 of these, 6 e–)

3p orbitals(3 of these, 6 e–)

4p orbitals(3 of these, 6 e–)

3d orbitals(5 of these, 10 e–)

1s2 2s2 3p62p6 4s2 3d103s2 4p6…1,2 3,4 5-10 11,12 13-18 19,20 21-30 31-36

Writing Electron Configurations:

Where are the e–? (probably)

As

HHe

N

Al

Li

Ti

Xe

1s2 2s2 3p62p6 4s2 3d103s2 4p6…

1s1

1s2

1s2 2s1

1s2 2s2 2p3

1s2 2s2 3p12p6 3s2

1s2 2s2 3p62p6 4s2 3d23s2

1s2 2s2 3p62p6 4s2 3d103s2 4p3

1s2 2s2 3p62p6 4s2 3d103s2 4p6 5s2 4d10 5p6

Sections of Periodic Table to Know

f-block

s-block

d-block

p-block

Three Principles about Electrons

Aufbau Principle:

for equal-energy orbitals,each must have one e– before

any take a second

Pauli Exclusion Principle:

e– will take lowest-energyorbital available

Hund’s Rule:

two e– in same orbitalhave different spins

1s22s2

3p6

2p6

4s23d10…

3s2

Friedrich Hund

Wolfgang Pauli

O

Orbital Diagrams

…show spins of e– and which orbital each is in

1s 2s 2p 3s 3p

1s 2s 2p 3s 3pP

S

Shorthand Electron Configuration (S.E.C.)

To write S.E.C. for an element:

1. Put symbol of noble gas that precedeselement in brackets.

2. Continue writing e– config. from that point.

Co

In

Cl

Rb

[ Ne ] 3s2 3p4

[ Ar ] 4s2 3d7

[ Kr ] 5s2 4d10 5p3

[ Ne ] 3s2 3p5

[ Kr ] 5s1

HAVE MOREENERGY

ARE FARTHERFROM NUCLEUS

AND

The Importance of Electrons

In “jogging tracks” analogy,the tracks representorbitals:

In a generic e– config (e.g., 1s2 2s2 2p6 3s2 3p6…):

regions of space where an e– may be found

# of energy level

# of e– in those orbitals

coefficient

superscript

In general, as energy level # increases, e–…

INVOLVED INCHEMICALBONDING

kernel electrons: valence electrons: in inner energy level(s);

close to nucleusin outer energy level

He: Ne:

Ar: Kr:

1s2 [ He ] 2s2 2p6

[ Ne ] 3s2 3p6

[ Ar ] 4s2 3d10 4p6

Noble gas atoms have FULL valence shells. They are stable, low-energy, and unreactive.

(2 v.e–) (8 v.e–)

(8 v.e–) (8 v.e–)

octet rule: the tendency for atoms to “want” 8 e– inthe valence shell

Other atoms “want” to be like noble gas atoms.

-- doesn’t apply to He, Li, Be, B (which want 2) or to H (which wants either 0 or 2)

fluorine atom, F 9 p+, 9 e–

** They give away or acquire e–.

steal 1 e–

9 p+, 10 e–

F atom would ratherbe F1– ion.

F1–

chlorine atom, Cl 17 p+, 17 e– steal 1 e–

17 p+, 18 e–

Cl atom would ratherbe Cl1– ion.

Cl1–

How to be likea noble gas…?

lithium atom, Li 3 p+, 3 e– lose 1 e–

3 p+, 2 e– Li atom would rather

be Li1+ ion.

Li1+

sodium atom, Na 11 p+, 11 e– lose 1 e–

11 p+, 10 e– Na atom would rather

be Na1+ ion.

Na1+

How to be likea noble gas…?

1+

Know charges on these columns of Table:

Group 1:Group 2:Group 13:Group 15:Group 16:Group 17:Group 18:

2+3+3–2–1–0

1+2+ 3+ 3– 2– 1–

0

Naming Ions

e.g., Ca2+ Cs1+

Al3+

Cations use element name and then say “ion”

e.g., S2–

P3–

N3–

O2–

Cl1–

Anions change ending of element name to “ide”and then say “ion”

calcium ion cesium ionaluminum ion

sulfide ionphosphide ionnitride ionoxide ionchloride ion

ENERGY(HEAT, LIGHT,ELEC., ETC.)

LightWhen all e– are in lowest possible energy state, an atom is in the ____________.ground state

e.g., He: 1s2

If “right” amount of energy is absorbed by an e–, it can“jump” to a higher energy level. This is an unstable,momentary condition called the ____________. excited state

e.g., He: 1s1 2s1

When e– falls back to a lower-energy, more stableorbital (it might be the orbital it started out in, but itmight not), atom releases the “right” amount ofenergy as light.

EMITTED LIGHTAny-old-value of energy to beabsorbed or released isNOT OK. This explainsthe lines of color in anemission spectrum.

Emission Spectrum for a Hydrogen Atom

Lyman series:

Balmer series:

Paschen series:

e– falls to 1st energy level

e– falls to 2nd energy level

e– falls to 3rd energy level

typical emission spectrum

H discharge tube, with power

supply and spectroscope

1ST E.L.

2ND E.L.

3RD E.L.

4TH E.L.5TH E.L.6TH E.L.

Lyman(UV)

Paschen(IR)

Balmer(visible)

~ ~ ~~ ~ ~

Resources - Atomic Structure

Objectives

Worksheet - vocabularyWorksheet - development of atomic theoryWorksheet - atomic number and mass numberWorksheet - ions and subatomic particlesLab - isotopesWorksheet - orbital diagramsWorksheet - electron configuration

Outline (general)

Worksheet - light problemsWorksheet - half-lifeTextbook - questions

Episode 6 - Atom