Chapter 4 and 16 Notes
Famous people and their contributions to Chemistry
Democritus
Propsed that matter was composed of indestructible particles
Named said particles “atoms” which is Greek for indivisible
Antoine Lavoisier
known as the Father of modern chemistry
developed the law of conservation of mass- a law that states that the mass of the reactants will equal the mass of the product in a chemical change
came up with the law of definite proportions- law that states that a compound always contains elements in a definite proportion
developed the law of multiple proportions- law that states that elements can combine in different ratios to create different compounds
John Dalton
published the Daltons atomic theory
Daltons atomic theory
each element is made of indivisible particles called atoms
atoms of one element have the same properties and mass that allows us to differentiate them from other elements
atoms can’t be created, destroyed or transformed into other atoms
atoms combine in a simple whole number ratio to form compounds
chemical reactions can combine, separate or rearrange atoms
Modern atomic theory
elements are made of small particles called atoms
atoms can’t be created or destroyed during ordinary chemical reactions
atoms are divisible and are made of protons, neutrons and electrons
all atoms of the same element have different masses
atoms of different elements are different
atoms combine in whole number ratio to form compounds
JJ Thompson
an english physicist who performed the cathode ray experiment
was the first detect a charged particle within the atom, which he identified as the electron
proposed the "plum pudding" model of the atom, suggesting that electrons are embedded within a positively charged "soup" which laid the groundwork for future atomic theories
Thompson’s Cathode ray experiment
He found that cathodes were attracted towards positive charges which shows that the cathodes were negative
He applied electric and magnetic fields to a beam of cathode rays and discovered that the deflection was the same for all gases
He used this information to calculate the charge-to-mass ratio using different cathode metals and different gasses
e/m = -1.76×10^8 coulombs/gram with coulomb being the SI unit for charge
Robert Millikan
an American chemist who performed the oil drop experiment which determined the mass of an electron
Millikan’s oil drop experiment
He let drops of oil fall between electrically charged plates and was able to suspend those drops by changing the voltage
he measured the mass of each drop and the total negative charge on each drop to find that the charge on the drop was always a whole number multiple which was e = 1.60× 10^-19
he then used Thompsons charge to mass ratio to figure out the mass of an electron which was 9.11×10^-28g
Ernest Rutherford
worked under Thompson to went go on to prove that positively charged atoms exist in the atoms
he also disproved the plum pudding model
Rutherford’s gold foil experiment
he charged positively charged alpha particles into a sheet of gold expecting all to pass through
but some were deflected which showed that atoms had a dense positive center which showed that most of the atom is empty space with a dense positive center
Rutherford’s nuclear theory of an atom
an atom has the same amount of protons and neutrons
the volume of the atom is mostly empty space with electrons being dispersed throughout
most of an atoms mass comes from the small dense positively charged core know as the nucleus
James Chadwick
a scientists that demonstrated the unaccounted mass in an atom due to neutrons
Dmitri Mendeleev
Called the father of modern periodic table
published a table of the elements organized by increasing atomic mass
Henry Moseley
He used his work with X-rays to determine the nuclear charge (atomic number) of the elements
he rearranged the elements in order of increasing atomic number
Periodicity- the fact that elements arranged in order of increasing atomic number have a periodic pattern in their physical and chemical properties
Atomic number- the number of protons in an atom
Mass number- the sum of protons and neutrons in an atom
Atomic mass- the weighted average of the masses of different isotopes of an atom
Atomic mass = (mass of one isotope)(percent abundance)+(mass of other isotope)(percent abundance)
Atomic mass is measured in amu (atomic mass unit)
Isotope- atoms of the same elements that have different numbers of neutrons
written in Element-mass number form. EX: Carbon-14
Ions- atoms of the same elements that have different numbers of electrons
written in Element then charge as an exponent form. EX: K+
Henry Bequerel
he experimented with uranium compounds
he noticed that mysterious energy was being emitted from the atom
the mysterious energy was a mixture of rays that went out in a straight line
some rays had more penetration power than others
Marie and Pierre Curie
discovered that the rays found by Bequerel were emitted by the uranium atoms
made contributions to the study of radioactivity
discovered radium and polonium
Radioactivity- the emission of radiation caused by the disintegration of an atoms nucleus
radioisotope is measured by the number of disintegration per second
the SI unit for radioactivity is Bequerel (Bq) which is 1 disintegration per second
Curie (Ci)- the number of the disintegration of 1g of Radium that occurs in 1 second
Radioactive decay- when an unstable nucleus randomly breaks down by emitting radiation
This occurs because of the unfavorable ratio of protons to neutrons
The nucleus adjusts itself and becomes more stable by emitting radiation
Radioactive decay continues as a decay series until the nucleus becomes stable
Types of radiations
Alpha radiation
releases a particle that’s similar in composition as Helium
has the lowest penetration power and can be shielded by paper and clothing
Beta radiation
releases a particle that’s similar in composition as an electron
has more penetration power but can be shielded by heavy clothing and lab gear
Gamma radiation
releases high energy radiation that doesn’t affect the identity of the atom
has the highest penetrating power and can penetrate through dense materials but can be shielded by lead and thick concrete
Positron emissions
releases a particle that is similar in composition as a positively charged electron
Transmutation- the conversion of on atom of an element into another atom of a different element
can happen naturally and artificially
Rutherford performed the first transmutation and converted nitrogen to fluorine by bombarding it with alpha particles
Chadwick supported is idea of a neutron by bombarding Beryllium with alpha particles which created free neutrons
Transuranium elements- elements beyond Uranium on the periodic table
the elements are artificially created in a particle accelerator
Nuclear Fission -the splitting of a large and radioactive nucleus into smaller fragments
Nuclear Fusion- when nuclei combine to form larger atoms
fusion requires extreme temperatures and efficient source of energy
Half-Life- the time it takes for 50% of the parent nuclei to decay to the daughter nuclei
Half life varies among isotopes
When graphed the half life looks like an exponential decay graph
Remaining = (original)(1/2)^ time elapsed/ half life