Notes Ch. 4 and 25: Atomic Structure and Nuclear Chemistry

History and Structure of the Nuclear Atom

The Atom

•smallest particle of an element that retains all properties of the element

Early Models of the Atom

Democritus (460 B.C. – 370 B.C)

•first to suggest the existence of ______

•believed atoms were indivisible and indestructible

Dalton

•Atoms of the same element are ______

•Each element is unique

•Atoms combine in fixed ratios to form compounds

Thomson

•Discovered ______

•Suggested atom looked like plum pudding (or a blueberry muffin or chocolate chip cookie) with electrons evenly distributed throughout positive sphere

Rutherford

•Conducted gold foil experiment

•Proposed atom is mostly empty space

•Concluded all positive charge and mass is concentrated in small region called ______

Bohr

•depicts the atom as a small, positively charged nucleus

•surrounded by electrons that travel in circular ______around the nucleus

Schrödinger

•model allowed the electron to occupy three-dimensional space like an electron “______”

•Used a mathematical equation to show a model of electrons as waves

More about the Atom

Size

•Teeny tiny

•observable with instruments such as a scanning tunneling ______

Parts (called Subatomic Particles)

Protons: p+

•charge = positive +1

•mass =1

Electrons: e-

•charge = negative -1

•mass ~0

Neutrons: no

•charge = zero

•mass = 1

Location of Parts

•Nucleus: center of atom

- contains protons and neutrons

- has a positive charge

- contains almost ALL of the ______of the atom

•Outside nucleus:

- contains ______

- has a negative charge

- occupies almost ALL of the volume of the atom

Atomic Charge

•______are NEUTRAL

•# of protons = # of electrons

(ALWAYS if you’re talking about an ATOM)

How Atoms Differ

Properties of Subatomic Particles

Particle / Symbol / Location / Relative
Charge / Relative mass / Actual mass (g)
Electron / e-or
e / 1- / 9.11 x 10-28
Proton / p+ or
/ 1+ / 1.673 x 10-24
Neutron / or / In the nucleus / 0 / 1.675 x 10-24

Atomic Number

•the number of ______in an atom

•Identifies element

–each atom has unique #

–# never changes

Mass number

•represents the ______of the number of ______and neutrons in the nucleus

•# of neutrons = mass number – atomic number

Isotopes

•Atoms of the same element but have a different # of neutrons

•Ex: 3 isotopes of carbon: Carbon-12, Carbon-13, Carbon-14

____# protons, ____# protons, ____ # protons

____# neutrons,____# neutrons,____ # neutrons

•All elements have isotopes (some 2, some 3, etc.)

•Some isotopes are naturally radioactive.

•Ex: Plutonium

Representing Isotopes

•In Ag-107, the 107 represents the mass number (neutrons + protons)

•the 47 represents the number of protons)

Practice:

1. What is the mass number for Co-59?

2. What is the mass number for ?

Atomic Mass

•The standard is the atomic mass unit (amu): defined as 1/12 of the mass of a carbon-12 atom

•the weighted average of the isotopes of that element.

•Formula:

Atomic mass of
an element / = / ( / % abundance
of
Isotope #1 / x / mass
of
Isotope #1 / ) / + / ( / % abundance
of
Isotope #2 / x / mass
of
Isotope #2 / ) / + / …

Practice 3

•Silver has two naturally occurring isotopes. Ag-107 has an abundance of 51.82% and mass of 106.9 amu. Ag-109 has a relative abundance of 48.18% and a mass of 108.9 amu. Calculate the atomic mass of silver.

Practice 4

• Rubidium is a soft, silvery-white metal that has two common isotopes, and . If the abundance of 85Rb is 72.2% and the abundance of 87Rb is 27.8%, what is the average atomic mass of rubidium?

Vocabulary to Know

•Atomic #- same # of protons & electrons

•Mass #-protons + neutrons

written 2 ways: Carbon-14 or C

•Isotopes-same # of protons, different # of neutrons

•Atomic mass-weighted average mass

Types of Radiation and Unstable Nuclei

I. Chemical and Nuclear Reactions

•Chemical reactions only involve an atom’s ______

•______reactions involve changing an atom’s nucleus

•Nuclear reactions release about a ______times more energy than chemical reactions

•Unlike chemical reaction, nuclear reactions are not affected by ______, pressure, or a catalyst.

II. Nuclear Vocabulary

•Radioactivity – the process of emitting ______

•Radiation - ______and particles emitted by a radioactive source.

•Radioisotopes – ______of atoms with unstable nuclei and emit radiation to obtain a more stable nuclei

•Radioactive decay -______nuclei losing energy by emitting radiation in a spontaneous process.

•Nucleon – refers to both ______and neutrons

III. Which Isotopes are Radioactive?

•Small Nuclei- Atoms which contain up to ______protons (up to Calcium) are usually ______.

•Large Nuclei- Larger nuclei tend to be ______.Allnuclei with ______or more protons (Polonium and up) are radioactive. For example, all isotopes of Uranium are radioactive.

•Atoms with more neutrons than protons- There are radioactive nuclei that have less than 84 protons. These nuclei have more neutrons than protons. For example, Carbon-12 (6 protons and 6 neutrons) is stable, while ______(6 protons and8neutrons) is radioactive.

IV. Why Does an Atom Undergo Radioactive Decay?

•Radioactive atoms emit radiation because their nuclei are ______.

•The stability of the nucleus depends on the ______to ______ratio

•Neutrons vs. protons graph stable nuclei found in a region called the band of______.

V. Types of Radiation – Alpha Radiation

•Alpha radiation are attracted to the negatively charged plate

•Alpha particles contain two protons and two neutrons (A ______nucleus)

•Blocked by______

•Least penetrating form of radiation (only travels a few centimeter in the air)

•Carry +2 charge

•Symbolized by ______or 

VI. Types of Radiation – Beta Radiation

•Beta radiation attracted to the positively charged plate

•Carry –1 charge

•Beta particles are fast moving ______

•Blocked by metal foil or ______

•Medium penetration power (travels a few meters in the air)

•Symbolized by _____ or 

VII. Types of Radiation – Gamma rays

•Gamma rays are high energy radiation that possesses no ______.

•Possess no electrical charge and are not deflected by magnetic or electrical fields.

•Not completely blocked by lead or ______

•The most penetrating and damaging type of radiation

•Carry no charge

•Symbolized by ______

VIII. Electron Capture

•Electron capture occurs when a nucleus of an atom draws in an ______.

• Rb + e → Kr

•Also known as ______capture

IX. Electrostatic Force

•Electrostatic force is when like charges ______and opposite charges ______.

X. Strong Nuclear Force

•that are extremely ______together. It keeps the nucleus ______.

Remember Mass Number and Atomic Number

XI. Writing and Balancing Nuclear Equations

•In a balanced nuclear equation, mass numbers and atomic numbers are ______.

Example

Th  Ra + He

–Notice the mass numbers and atomic numbers add up to the same on both sides of the equation

Practice

Zr  e+ ?

Po  He + ?

?  Rn + He

Ca  e + ?

Cm  He + ?

Transmutation

Transmutation

•Transmutation - The conversion of one element to ______element.

•All nuclear reactions are transmutation reactions except for ______emission, which does not alter an atom’s atomic number.

Induced Transmutation

•Before 1919, the only way to change the nucleus or cause transmutation was to wait for ______.

•In 1919 Rutherford was the first to induce (______) transmutation.

•He proved that nuclear reactions can be produced ______.

•Induced transmutation can occur by ______an atom with alpha particles, protons or neutrons.

Transuranium Elements

•Elements with atomic number above ______.

•All transuranium elements undergo transmutation

•None of the transuranium elements occur in ______and have only been produced through induced transmutation.

Half-life

•The time required for ______of a radioisotope’s nuclei to decay into its products

•After each half-life, half of the existing radioactive atoms have decayed into atoms of a ______element

•Amount remaining at time T = (initial amount)(1/2)n

where n= number of half-lives

•n = total time ÷ time of one half-life

Practice

Scientists start with 50.0 g sample of a radioisotope. How much is left after four half-lives?

Iron-59 is used in medicine to diagnose blood circulation disorders. The half-life of iron 59 is 44.5 days. How much of a 2.000 mg sample will remain after 133.5 days?

V. Carbon-14 Dating

•Carbon 14 dating is the process of determining the ______of artifacts that were once part of a living organism by measuring the amount of 14C ______in that artifact

•Carbon-14 is radioactive and undergoes beta decay. It has a half-life of 5730 years.

Carbon-14

•14C evenly spread in the Earth’s biosphere

•Plants incorporate 14C into their structure that matches the level in the atmosphere.

•When an organism dies, 14C declines at a known rate. (Half-life of C-14 = 5730 years)

•Comparing the remaining14Cfraction of a sample to that expected from atmospheric14Callows the age of the sample to be estimated.

•Dates carbon-bearing materials up to 62,000 years.

•Carbon-14 Decay

style

•Using the graph, about what % of carbon-14 remains after 11, 400 years?

Fission and Fusionof Atomic Nuclei

I. Nuclear Fission

•Fission - The splitting of the nucleus into ______(division)

•Uranium-235 is struck by a neutron and forms Ba-141, Kr-92, and additional neutrons.

II. Chain Reaction

•Chain reaction

– Nucleus captures a neutron and splits into fragments and produces three neutrons

–______start a new reaction

•Critical mass

– The ______mass required to support a self-sustaining chain reaction

III. Nuclear Fusion

•Fusion - ______atomic nuclei to produce a nucleus of greater ______

•Fusion reactions release ______energy than fission reactions

•The ______is powered by fusion

IV. Nuclear Binding Energy

•The energy required to break a nucleus into its individual protons and neutrons

•Energy released in a nuclear reaction is much ______than in chemical reactions

V. Mass Defect

•When breaking apart a nucleus, there is a change in mass called the mass defect.

•The change in mass was converted to energy.

•We know this as E=mc2

VI. Nuclear Reactors

•The purpose of nuclear reactors is to keep the chain reaction going without letting it get out of control

VII. Nuclear Bombs

Atomic Bomb

•Uses______

•Uses enriched uranium-235 or plutonium

•Nagasaki and Hiroshima

Hydrogen Bomb

•Uses ______

•1000 time more powerful than atomic bomb

•Uses deuterium 2H and tritium 3H