Early Atomic Theory and Structure

Chapter 5—Early Theorieso What is stuff

made of? o What makes

something move?o How do we know

it’s alive? o Is there a

fundamental particle that everything is made up of?

o Is there a universal constant to all matter?

Chapter 5.1 Early Thoughtso Roots of atomic

theory are as old as 440 B.C. with Democritus’ idea of the atom

o It took 2 000 years for us to expand on this idea. The new theory was to be done by an English schoolmaster John Dalton in the early 1800s.

Dalton’s Atomic Theoryo His theory included 6 postulateso 1. Elements are made up of atomso 2. Atoms of the same element are alikeo 3. Atoms of different elements are different

by virtue of their size and masso 4. Chemical compounds are formed by the

union of two or more atoms of different elements

o 5. Atoms combine to form compounds in whole number ratios (1:2 or 2:2, etc]

o 6. Atoms of two elements may combine in different ratios to form more than one compound

5.2 Dalton’s Atomic Theory (cont.)

o Why is it a Theory?

o Which are still true? o Which do we knowMore info about now?

5.3 Composition of Compounds

o The Law of Definite Composition states that a compound always contains two or more elements combined in definite proportion by mass

Law of Multiple Proportionso The Law of Multiple

Proportions states that atoms of two or more elements may combine in different ratios to produce more than one compound

5.4 - 5.8 Subatomic Particles

o Through the years of the late 1800s and into the early 1900s it was determined that there are three subatomic particles

o Electrons (discovered first)o Protons (reasoned to exist if

elements are neutral)o Neutrons (discovered last)

Electrons o1. Electron which

occupies the area outside the nucleus and has a negative charge, relative to the other subatomic particles it has negligible (so small that it can be ignored) mass.

Protonso2. Proton which exists in

the nucleus, has a positive charge and has mass roughly equal to neutrons

Neutrono3. Neutrons (discovered

last] functions as the glue that holds the nucleus together so that the protons don’t repel each other, it has no charge and roughly the same mass as the proton

IsotopesoIsotopes have same number of protons (so they are the same element) but different number of neutrons

oSome isotopes are radioactive

Atomic NumberoAtomic Number = the

number of protons; unique to each element and the way the periodic table is arranged

Mass number oMass Number = protons + neutrons (whole number

oCannot be found on the periodic table!

Check yourselfo The nucleus is made up of

what two types of subatomic particles?

Formulas you should knowo Atomic number = # of protonso In an atom (uncharged):

o # of protons = # of electronso Mass # = # protons + #

neutrons oro # neutrons = mass # - # protonso Charge = # protons - # electrons

(for ions)o Remember the atomic # and # of

protons give the element its identity and does not change

Elements composed of atomsElements or atoms in an unbonded state have the same number of electrons as protons

(They are neutral)

IonsIons have an unequal number of electrons and protons. An atom loses or gains electrons to take on a charge (protons/neutrons are not transferred)

Charge = #protons - # electrons

Ionic Chargeo Charge is written in the upper

RIGHT corner of the element’s symbol.

o It is written with the number first and the sign second unless it is a + 1 or a -1 in which case it is just written as + or -.

o Negative ions change their names to end in –ide like fluorine is fluoride

Ionic Notation

X3-This means that this

element has a -3 charge.

Self Checko What is the charge of a

substance with 14 protons, 15 neutrons, and 14 electrons?

Self Checkero If a substance has a charge

of +2, this means that the number of protons is (circle one: LESS than or GREATER than) the number of electrons?

ISOTOPIC NOTATIONisotopes are atoms with the same number of

protons but different number of neutrons A

Z XA = mass number (the total number of protons +

neutrons)Z = atomic number (the total number of protons)X = element symbol

READING ISOTOPIC NOTATIONREADING ISOTOPIC NOTATION 46

21 Sc46 = mass number (the total number of protons (2121) +

neutrons (2525)21 = atomic number (the total number of protons (2121))Sc = element symbolIn a neutral atom, the number of electrons (21) is

equal to the number of protons.

PRACTICE PROBLEMS

15N # protons = ____ # neutrons= ____ #electrons

= ___35P # p = ____ # n= ____ #e- = ___

62Cu2+ # p = ____ # n= ____ #e- = ___

76Se3- # p = ____ # n= ____ #e- = ___

7 8 7

15 20 15

29 33 27

34 42 37

Writing ISOTOPIC NOTATION1. Write the symbol for the atom with an atomic

number of 21 and a mass number of 48.

2. Give the complete chemical notation for the nuclide with 23 protons, 26 neutrons and 20 electrons.

3. Write the isotopic notation fora. Z = 46 A = 110b. An atom containing 24 protons, 28

neutrons, and 21 electronsc. Titanium-50

48 Sc

49V3+

110Pd

52Cr3+

50Ti

PRACTICE PROBLEMS1. 196 Pt4+

# p = _____ # n = _____ #e- = _____

mass number = ________ atomic number = _______

atomic mass = ________ name of element = _______

2. Indicate the appropriate atomic mass of an element with 30 protons, 30 neutrons, and 28 electrons.

78 118 74

196 78

195.1 amu platinum

65.39 amu

Atomic MassoAtomic Mass = number

on the periodic table reflecting the mass all isotopes known and their relative percentages (on periodic table below element’s symbol--usually not a whole number)

Atomic Masso The atomic mass of an element represents

the average mass of all the isotopes found in nature. No element exists with only one possible isotope. Hydrogen has the smallest number of isotopes: 1H protium, 2H deuterium, 3H tritium. Its atomic mass is 1.0079 amu (atomic mass units). The atomic mass is calculated by adding the % of 1H mass found in nature to the % of 2H mass found in nature plus the % of 3H mass.

o % 1H + % 2H + % 3H = average mass (atomic mass)

o Generally the formula used is: % X + % Y + % Z… = atomic mass.

An instrument called the mass spectrometer is generally used to determine the percentages and individual masses of each isotope.

Atomic Masso Silver is found to have two stable isotopes, one

has an atomic mass of 106.904 amu and the other weighs 108.905 amu. The first isotope represents 51.82 % of the mass of the element and the second represents 48.18 %. What is the atomic mass of the element silver?

The equation to use is %X + % Y = averageAnd remember to turn your percents into fractions

before multiplying.

(0.5182) 106.904 amu + (0.4818) 108.905 amu =?55.398 amu + 52.470 amu =?

107.868 amu !! Now look at the periodic table to verify the answer.

PRACTICE PROBLEMS # 81. A sample of neon contains three isotopes, neon-20

(with an isotopic mass of 19.9924 amu), neon-21 (20.9939 amu) and neon-22 (21.9914 amu). The natural abundances of these isotopes are 90.92%, 0.257 %, and 8.82 %. Calculate the atomic weight of neon.

2. There are only two naturally occuring isotopes of copper, 63Cu and 65Cu. Copper has an atomic mass of 63.55 amu. What is the natural abundance of each isotope?

3. There are only two naturally occuring isotopes of gallium, 69Ga and 71Ga. What is the natural abundance of each isotope?

20.17 amu

65Cu = 30% & 63Cu = 70%

69Ga = 60% and 71Ga = 40%

GROUP STUDY PROBLEM #8_______1. The element with atomic number 53 containsa) 53 neutrons b) 53 protons C) 26 neutrons & 27 protons d) 26 protons & 27

neutrons

_______2. The mass of one atom of an isotope is 9.746 x 10-23 g. One atomic mass unit has the mass of 1.6606 x 10-24 g. The atomic mass of this isotope is

a) 5.870 amu b) 16.18 amu c) 58.69 amu d) 1.627 amu

108

_______3. The number of neutrons in an atom of 47 Ag isa) 47 b) 108 c) 155 d) 61

27

_______4. The number of electrons in an ion of 13 Al3+ isa) 13 b) 10 c) 27 d) 14

_______5. What is the relative atomic mass of boron if two stable isotopes of boron have the following mass and abundance:

10.0129 amu (19.91%) & 11.0129 (80.09%)a) 10.81 amu b) 10.21 amu c) 10.62 amu d) 10.51 amu

Test your KnowledgeName Symbol Atomic

## of

protons# of

neutronsMass # # of

electrons

Neon

11

Pb 20774 110

88 226Carbon 8

F 1979 118

Test your KnowledgeName Symbo

lAtomic

## of

protons# of

neutrons

Mass #

# of electro

ns

Neon

Ne 10 10 11 21 10

Lead

Pb 82 82 125 207 82

Tungsten W 74 74 110 184 74

radium

Ra 88 88 138 226 88

Carbon

C 6 6 8 14 6

fluorine

F 9 9 10 19 9

Gold Au 79 79 118 197 79

Table Information

Hydrogen

Symbol H Atomic Number 1 Atomic Weight 1.00794 Oxidation States +1, -1 Electronegativity, Pauling 2.2 State at RT Gas, Non-metal Melting Point, K 14.01 Boiling Point, K 20.28

The Periodic Table o Horizontal rows are called

periodso Vertical columns are called

groupso We will use 1- 18 as group

designations. o Group 1 is Alkali Metalso Group 2 is the Alkaline Earth

Metalso Group 18 Inert or Noble Gaseso Group 17 Halogens

Larger Groupso Groups 3 –12 are the heavy

metals or transition elements

o Two periods at the bottom are called the rare earth elements or the inner transition elements.