Atomic Structure

ChemistryMrs. Hayen

History of the Atom:Time Line

• Find the following scientists in your textbook. They are not given to you in the order they are found in the text. That would be too easy! Some may be found in other chapters besides 4 & 5!!

• Write down the years they were alive or the year that their main discovery was made.

• Write down their contributions to the development of today’s model of the atom.

• Create a creative, colorful, and informative timeline!

Scientist to Include on Timeline:

• Rutherford

• Millikan

• Dalton

• Marie and Pierre Curie

• Democritus

• Thompson

• Roentgen

• De Broglie

• Heisenberg

• Chadwick

• Bohr

• Aristotle

What is an Atom?

• Atom – The smallest particle of an element that retains the properties of the element.

• How big is an atom? VERY SMALL!!!• World Population 6,000,000,000• Number of Atoms in a penny:

29, 000,000,000,000,000,000,000• Scanning tunnel microscope allows us to see

atoms

Introduction to the Atom• Atomic structure vocab: a review.• Follow along and fill in the definition as we review them

together:On the Table “Subatomic Particle Organizer” Handout

– Proton– Neutron– Electron

On the “Periodic Square” Handout– Label atomic number, atomic mass, chemical symbol– What does each tell you?– Isotope, notations for isotopes– Average abundance, definition & how to understand/calculateWhat is a

mass number?– What is an ion? How do you write one?

Atoms: the basics• A different number of protons in the atom means:

A new____________ altogether• A different number of neutrons in the atom

means:A new ____________ of the same element

• A different number of electrons in the atom means:

A new _____________ of the same element

element

isotope

ion

Atomic Mass Unit

• Abbreviated: amu• Chemists developed a method of measuring the

mass of an atom without using very small numbers in scientific notation.

• They chose an atomic standard: Carbon-12• They agreed the mass of Carbon-12 was 12 amu.• Therefore, 1 amu is 1/12 the mass of a Carbon-12

atom.

Why is the atomic mass not a whole number?

• Atomic masses have decimals!

• Atomic mass – weighted average mass of the isotopes of that element.

• For Example: Mass of Cl is 35.453

• Isotopes: 75% Chlorine-35

25% Chlorine-37

Example on handout… (end of atomic basics)

Mapping out electron configuration

• Principle Quantum Number – Energy level where the electron(s) is(are) found (AKA “n” and coincidentally the row of the PT)Examples: n= 1, 2, 3, 4, 5, 6, 7

• As “n” increases, electrons:– are farther from the nucleus– expend higher amounts of energy

 

Rationale: Electrons are lazy, so they want to be as close to the nucleus as they can so they can expend the LEAST amount of energy.

Mapping out electron configuration

• How many energy levels does hydrogen have (what is n for this element)?

• Helium?

• Lithium?

• Sodium?

• Calcium?

• Xenon?

Mapping out electron configuration

Each energy level has a maximum capacity for electrons. Maximum in each level = 2n2;

where n= 1, 2, 3, 4, 5, 6, 7• Example: for n =1:

max = 2(1)2 electrons• You solve for: n = 2

n = 3n = 4

= 2 electrons

Mapping out electron configuration• Sublevels – subdivisions of “n”

(sections of seats within a row)• The number of sublevels in each energy

level is equal to n. Therefore:n = 1 has one subleveln = 2 has two sublevelsn = 3 has three sublevelsn = 4 has four sublevels

n = 5 has five sublevels but the fifth one is not used in ground state elements.

Mapping out electron configuration

• The names for the various sublevels are s, p, d, f.• The first sublevel in any level is always s; the

second is p; third is d; fourth is f.Therefore:• if n = 3 & it has 3 sublevels, their names are

s p d• if n = 2 & it has 2 sublevels, their names are…?• if n = 1 & it has 1 sublevel, its name is…?• if n = 4 & it has 4 sublevels, their names are…?

Mapping out electron configuration

• Orbitals – Each sublevel (section in a row) has specific orbitals (seats in a section) for electrons.

• Each orbital (seat) can hold 2 electrons. Therefore, the maximum number of electrons in the s

orbital is 2.• S has 1 orbital; maximum electrons = • P has 3 orbitals; maximum electrons = • D has 5 orbitals ; maximum electrons = • F has 7 orbitals; maximum electrons =

• Three Main Rules Electrons Abide By:• Aufbau principle (“Electrons love the nucleus”):

each successive electron occupies the lowest energy orbital available.

• Pauli Exclusion Principle (“Two to Tango”): a maximum of two electrons may occupy a single atomic orbital, but only if the electrons have opposite spins.

• Hund’s Rule (“Spread ‘em out”): Single electrons with the same spin must occupy each equal-energy orbital before additional electrons with opposite spins can occupy the same orbital.

Mapping out electron configuration

• Orbital Diagrams

Used to show how electrons are distributed within sublevels and to show the direction of spin.

• Boxes are used to represent orbitals (“seats”). and arrows are used to represent electrons.

• Beware of filling sections out of order!!!

Mapping out electron configuration

• The first electron in the orbital is represented by an arrow pointing up, , meaning clockwise spin.

• Once you add a second electron, it is represented by an arrow pointing down, , meaning counterclockwise spin.

• An electron configuration notation is an abbreviated form of the orbital diagram.

Mapping out electron configuration

• Electron Dot Diagrams• Valence Electrons – electrons in the atom’s

outermost energy level. These electrons:- are involved in forming chemical bonds.- are represented visually by an electron dot structure.

• Also known as Lewis Dot Formulas.• Examples:

Mapping out electron configuration

Energy Level = row in a theatre

NucleusSublevels = sections in a row

Orbitals =

seats in a section

Summary for electrons…

• Orbital Diagram—draw the boxes

• Electron Configuration—the shorthand (in numbers and letters) that represent the orbital diagram

• Lewis Dot Diagram—simplified notation showing only valence electrons

4.4 Unstable Nuclei and Radioactive Decay

• Late 19th century scientists noticed some elements spontaneously emitted energy and particles called radiation.

• Elements that give off radiation are said to be radioactive.

• Thus, atoms are not unchangeable as Dalton once thought.

• Nuclear reactions – a reaction that involves a change in the nucleus of an atom.

• Radioactive decay – when nuclei are unstable and gain stability by emitting radiation.

• Fill out the Chart for Types of Radiation

Information from Chapter 25

• Transmutation – conversion of an atom of one element to an atom of another element by spontaneous emission of radiation.

• Induced Transmutation – nuclear reactions produced artificially by striking a nucleus with a high-velocity charged particle.

• Transuranium elements – all elements after Uranium on Periodic Table. – Produced in laboratory by induced

transmutation– All are radioactive

Radioactive Decay Rates

• Half-life – the time required for one-half of a radioisotope’s nuclei to decay into its products. (see table 25-4)– Ex. Strontium-90 half life is 29 years

• If today I have 10.0 g, in 29 years I would have 5.0g

• In another 29 years (total of 58), I would have 2.5 g

Radiochemical Dating

• Chemical reactions: greatly affected by temperature, pressure, and concentration and presence of catalyst.

• Nuclear reactions: NOT affected by anything. Half lives are constant!

• Because of this, radioisotopes can be used to determine age of objects

• Radiochemical dating – process of determining the age of an object by measuring amount of radioisotope remaining.

• Example: Carbon dating used to age artifacts once living.

Nuclear Fission/Fusion

• HUGE amounts of energy produced by Nuclear reactions.

• Nuclear Fission – splitting of a nucleus into fragments to become more stable.

• Used in nuclear power plants (controlled)

• And nuclear bombs (uncontrolled)

• Nuclear Fusion – Combination of nuclei to form a more stable nucleus.

• Large energy released!• Sun powered by Fusion of hydrogen into

helium. • Requires extremely high temperature to

occur.• Scientist researching Cold Fusion

Types of Radiation

• Fill out chart on Alpha, Beta, and Gamma