Chapter 3 Notes Atomic Structure

Chapter 3 Notes Atomic Structure

Students will understand the development of atomic theory

I. Early Atomic Constructs A. What are atoms

1. Democritus- 450 BC Greek, determined matter was composed of ATOMOS▪ A finite piece of matter, considered the smallest

peice 2. Modern Definition- Atoms are the

smallest piece of “organized” matter of an element having properties of that element

3. Aristotelian Science- Held that all matter was composed of 4 basic elements… earth/air/fire/water

I. Early Atomic Constructs A. What are atoms (cont)

4. Robert Boyle (circa 1660)- Performed quantitative experiments on atoms▪ a. investigated behavior of gases▪ Created Boyles Law: The volume of gas is inversely

proportional to the pressure (V = 1/P) As the volume of the gas increases the pressure decreases

and as the volume of the gas decreases the pressure increases

5. Joseph Priestly (circa 1770)- Investigated air▪ a. determined air to be a vital substance for life▪ b. determined photosynthesis produced oxygen


6. Antoine Lavoisler (circa 1790)- Disproved ‘Phlogiston’ theory of George Stahl▪ a. Conducted quantitative experiments about

burning.▪ b. Names Priestly’s gas to be oxygen▪ c. Experimentally demonstrated ‘The Law of

Conservation of Mass’ 7. Joseph Proust (circa 1799)- Extended

Lavoisler’s concepts


7. Proust (cont)-▪ a. Demonstrated the ‘Law of Definite Proportion’▪ A compound will have the same proportion of element

throughout▪ Also stated, a given compound will always contain the same

proportion of elements by weight 8. John Dalton (circa 1803)- Builds on Proust’s

concepts▪ a. Derives the ‘Law of Multiple Proprotions’▪ 2 elements that form a series of compounds (ex. CO, CO2)

combine to give ratios that reduce to a whole number by weight


8. Dalton (cont)-▪ b. Determined some of those elements can form

more than one compound▪ c. Expanded on ideas from the Greeks and Boyle to

derive the Atomic Theory of Matter▪ 1. elements are composed of identical atoms▪ 2. atoms of an element are identical, in all aspects▪ 3. atoms of different elements differ in mass▪ 4. atoms combine to form compounds in a definite

proportion (this was Proust’s theory)▪ 5. atoms are not created nor destroyed during a chemical

reaction


9. Joseph Gay-Lussac (circa 1809)- Conducted experiments on gases▪ a. Determined that gases under controlled

temperature and volume have a specific behavior▪ A given volume of gas reacts to produce a given

volume of product 10. Amedeo Avogadro (circa 1811)-

Introduced the concept of molecules


10. Avogadro (cont)▪ a. Determined that equal volumes of gas contain

equal numbers of atoms/particles/molecules▪ b. His work was ignored until Einstein (proved N=

6.023 X 1023, Avogadro’s number)▪ Avogadro’s number is the number of atoms or molecules in a

given amount of gas (a mole of gas) 11. Jons Jakob Berzelius (circa 1820)- ▪ a. Established the modern symbol system for

elements ▪ b. Discovered Cerium, Selenium, Silicon, and Thorium


12. Michael Faraday (circa 1839)-▪ a. Determined atomic structure is related to

electricity

I. Early Atomic Constructs B. Discovering Atomic Structure

1. General Information▪ a. Faraday’s discoveries were correct▪ Atoms contain particles that have electrical charge

2. Static Electricity▪ a. Electricity comes from the greek word

elekton (the word for amber)▪ Used the word because when amber was rubbed with

a cloth the amber would attract dust


(cont) 2. Static Electricity (cont)▪ b. Benjamin Franklin studied electricity and

determined an object would have 2 charges ( + positive and – negative)▪ Determined 2 like charges repel each other▪ Determined 2 opposite charges attract each other▪ Determined charges can collect on one object and

then become attracted to another object The charge can jump across open spaces (static

shock!) The moving stream of electron charge is called a

current


(cont) 3. Cathode Rays and Electrons▪ a. a cathode tube is an evacuated glass tube▪ b. on each end of the tube are wires

connected to two ends of a battery▪ c. one end of the tube is connected to the

positive end of the batter (anode) and the other end is connected to the negative end of the battery (cathode)▪ d. inside of the tube is a fluorescent material▪ e. a stream can be seen inside of the tube


(cont) 3. Cathode Rays and Electrons (cont)▪ f. since the stream comes from the negative

end, it was called a Cathode Ray▪ The Cathode Ray is responsible for the creation of

the TV picture The ray can move a paddle The movement proves the electron is a particle Magnets can deflect the beam, suggesting the

particle was negatively charged


(cont) 3. Cathode Rays and Electrons (cont)▪ g. J.J. Thomson attempted to determine the

mass of an electron▪ Used a specialized Cathode Ray tube with a small

hole in it▪ Used a magnet and a electrically charged plate▪ The magnet and the plate would ‘bend’ the ray

▪ h. Thomson repeated the experiment using different gases▪ Used mathematical equations to predict how far each

cathode ray would bend (with each new gas)


(cont) 3. Cathode Rays and Electrons (cont)▪ h. (cont)▪ Named the beams electrons▪ Determined the ratio of the electron charge to the

mass as 1.76 X 108 coulambs/gram▪ Thomson concluded:

Electrons are negatively charged Electrons are particles Electrons charge ratio to mass is 1.76 X 108

coulambs/gram


(cont) 3. Cathode Rays and Electrons (cont)▪ i. Robert Millikan- Used oil droplets to

determine the charge of an electron▪ 1.60 X 1o-19 C (Coulamb)▪ He was able to determine the mass of an electron as

well 9.11 X 10-28 g The electron is 2000(x) lighter than an atom of

Hydrogen


(cont) 4. Radioactivity▪ a. Henri Bequerel discovered radioactivity▪ He placed a piece of uranium on unexposed film and

it made an image▪ He helped discover 2 other radioactive elements

Radium and Polonium▪ b. Radioactivity accompanies fundamental

changes in the atom▪ Chemical properties change as the element gives off

radiation▪ Radiation is the emission of particles/rays from an

element

I. Early Atomic Constructs B. Discovering Atomic Structure (cont)

4. Radioactivity (cont)▪ c. Ernest Rutherford studied radioactivity▪ Using 2 electrically charged plates he was able to see 2

types of radiation Alpha radiation – Deflected toward the negative plate Beta radiation – Deflected toward the postivie plate Gamma radiation – (discovered later) is not deflected

in either direction▪ d. Alpha and Beta rays are particles▪ Alpha particles have a 2+ charge▪ Beta particles are considered high speed electrons

I. Early Atomic Constructs B. Discovering Atomic Structure (cont)

4. Radioactivity (cont)▪ e. Gamma radiation acts like X-rays and are not

particles▪ (Go to Types of Radioactive Decay Notes Here!)

5. The Nuclear Atom▪ a. An atom has no charge (electrically neutral)▪ b. Since there are negatively charged particles, there

must be positively charged particles▪ Rutherford was determined to discover where the positively

charged particles were located▪ c. Alpha (radiation) particles were shot at gold foil


(cont) 5. The Nuclear Atom (cont)▪ d. most passed through without a deflection▪ e. some were deflected at great angles▪ The deflection was dependant on the angle of impact

with the nucleus of the gold atom (Au)▪ f. This demonstrated that there was a nucleus

to an atom and that the positive charge was within the nucleus

I. Early Atomic Constructs C. Modern Atomic Theory

1. General Information▪ a. atoms have 3 fundamental paricles▪ Protons– positively charged particle (p+)▪ Neutrons– particles which carry no charge (n0)▪ Electrons – negatively charged particles (e-)

2. The Structure of the Atom▪ a. The nucleus contains 2 of the particles▪ Protons and Neutrons▪ Neutrons have a slightly greater mass than a proton▪ Protons are 2000 (x) greater in mass than an electron

I. Early Atomic Constructs C. Modern Atomic Theory (cont)

2. The Structure of the Atom (cont)▪ b. Rutherford visualized the atom as a

miniature solar system▪ The nucleus in the middle▪ The electrons have different orbitals to circle around

the nucleus▪ The proton’s charge has been simplified to +1▪ The electron’s charge has been simplified to -1▪ The atomic masses have been abbreviated and

expressed as Atomic Mass Units (AMU)


3. Atomic Numbers▪ a. Henry Moseley discovered each atom had a

unique positive charge▪ b. each atom has a different positive charge▪ Each positive charge is a proton, each atom has a

different number of protons▪ c. The Atomic Number equals the number of

protons▪ d. Since each atom is electrically neutral, the

positive charges must equal the negative charges


4. Ions▪ Charged atoms▪ Atoms can gain or lose electrons▪ Causes the atom to have a net charge (either positive or negative)▪ Example : H+ is the hydrogen ion because it lost 1 electron▪ Ions with more positive (protons) than negative (electrons) charges

is positive▪ Ions with more negative (electrons) than positive (protons) charges

is negative▪ Determining the net charge of the atom is easy…▪ Charge of ion = [# of p+] – [# of e-]

▪ The loss or gain of an electron doesn’t change the name of the atom (i.e. Hydrogen ion)


5. Isotopes▪ a. Dalton’s second postulate isn’t exactly true…▪ ‘All atoms of a given element are identical’▪ All atoms of a given element do not have the same number

of neutrons▪ Atoms that have the same number of protons but different

numbers of neutrons are called Isotopes Most elements in the first 2 rows have at least 2 isotopes

▪ b. In nature elements are almost always found in a mixture of isotopes▪ The elements isotopes typically are found in the same

percentages


5. Isotopes (cont)▪ c. To identify isotopes, a number is added before the symbol

or name, the mass number▪ The mass number is the sum of the protons and the

neutrons in an atom For example: Oxygen has 8 protons and 8 neutrons

(most of the time) or Oxygen has 8 p+ and 7 neutrons (a very small amount of the time), this is an isotope of oxygen This is why Oxygen's atomic mass is 15.9994, not 16

For example: an atom with 17 protons and 20 neutrons We know by the protons it is Chlorine (Cl) and is called

Chlorine-37 or 37Cl.


6. The Mass of an Atom▪ a. Always measured in Atomic Mass Units

(AMU)▪ b. Defined as the mass of either a proton or a

neutron (loosely defined)▪ c. The mass of an atom in AMU is

approximately the sum of the number of protons and neutrons (not exactly, we just learned about isotopes!) example: Oxygen is approximately 16 AMU (8 p+ and 8 no)


6. The Mass of an Atom▪ d. The real AMU for an atom includes the

Isotopes by percentage, thus it is called the Average Atomic Mass▪ Chlorine has two isotopes:

Element Mass # Mass (AMU) Percentage % AMU

Chlorine 35 34.969 75.53 26.412

Chlorine 37 36.966 24.47 9.0455

Ave AMU= 35.45

Carbon 12 12.0 98.89 11.866

Carbon 13 13.003 1.11 0.144

Ave AMU= 12.01

I. Early Atomic Constructs D. Nuclear Reactions

1. General Information▪ a. Are the changes in an atom’s nucleus▪ b. The reactions change the composition of

the atom’s nucleus▪ c. There are 3 types of nuclear reactions▪ Alpha, Beta, and Gamma rays

▪ d. Radioactivity is the spontaneous emission of radiation from the nucleus of an atom


2. Nuclear Stability▪ a. Most atoms are stable in nature▪ b. Why are they stable?▪ The combination of protons and neutrons are nearly

equal▪ There is enough space in the nucleus for the protons

to be close together▪ c. A ‘Strong Nuclear Force’ overcomes the

repulsive force of like charges▪ It is only encountered with subatomic particles


2. Nuclear Stability▪ d. Stable nuclei follow a distinct pattern▪ Elements 1-20 have equal numbers of protons and

neutrons▪ Atomic #s greater than 83 (can’t have enough

neutrons) therefore all are radioactive▪ e. If too many neutrons, the nucleus is

unstable as well, and it will emit Beta radiation▪ f. Heavy isotopes and light isotopes are also

radioactive

I. Early Atomic Constructs E. Radioactivity

1. Types of Radioactive Decay (A closer look)▪ a. Alpha Radiation (Decay) is a stream of Alpha

particles▪ An alpha particle consists of 2 protons and 2 neutrons

Is represented by 42He or 4

2α▪ Alpha particles do not penetrate the skin well

▪ b. Beta Radiation (Decay) is a stream of high speed electrons▪ The electrons come from the nucleus, not the orbitals▪ Neutrons change into protons and electrons

The protons stays in the nucleus Is represented by 0

-1 e- or 0-1 β

I. Early Atomic Constructs E. Radioactivity (cont)

1. Types of Radioactive Decay (A closer look) (cont)▪ b. Beta Radiation is a stream of high speed

electrons (cont)▪ 100 (x) greater penetration of the skin/body then alpha

particles▪ Can damage skin (skin cancer)

▪ c. Gamma radiation is a form of light▪ Similar to X-rays in behavior

Is represented by 00γ

▪ Accompanies alpha and beta decay

I. Early Atomic Constructs E. Radioactivity (cont)

1. Types of Radioactive Decay (A closer look) (cont)▪ c. Gamma radiation is a form of light (cont)▪ Has the greatest damage to the body/skin▪ Lead and concrete barriers can stop gamma radiation

2. Elemental Radioactive Decay▪ a. the original nucleus decomposes and becomes a

new nucleus (always subtract from the original element)▪ Ex. 226

88Ra 42He + 222

86Rn (alpha decay)▪ Ex. 131

53I 0-1β + 131

54Xe (beta decay)

I. Early Atomic Constructs

Chapter 3 Notes Atomic Structure

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