Chapter 3
Dalton's Atomic Theory
1. All matter is made up of extremely small particles called atoms. 2. Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties. 3. Atoms cannot be subdivided, created nor destroyed 4. Atoms of different elements can combine in fixed, small, whole number ratios to form compounds 5. Chemical reactions involve the combining, separating or rearrangement of atoms to form new substances
charge of a single electron
1.6 x 10^-19
Problems with Dalton's Atomic Theory
2. atoms of a given element are not identical in mass because isotopes of the same element have different masses, 3. Atoms can be subdivided into subatomic particles (electrons, neutrons, protons)
Avogadro's number
6.02x10^23, used to calculate molar mass, number of particles in a molecule
example of finding the average atomic mass
Boron is 19.9% ^10 B and 80.1% ^11B. ^11B is 80.1 percent abundance on earth. to find atomic weight: .801(11u)+.199(10u) and check on the periodic table
standard
Carbon-12 (6 protons and 6 neutrons) is the mass standard. 1u= 1/12th the mass of a carbon-12 atom
Cannon Ball
Dalton's model of an atom, solid sphere, no subatomic particles
Thomson
Developed the plum pudding model of the atom in which the atom is a ball of positive charge with negatively charged electrons embedded throughout
alpha particles
He without electrons, 4/2 (mass number: 4, atomic mass: 2), positive charge, least amount of energy, smaller than an atom
Ernest Rutherford
New Zealand, responsible for the modern nuclear view of the atom, shot alpha particles through gold foil, credited with the discovery of the nucleus!
Gold Foil Experiment
Rutherford was trying to prove the Plum Pudding model, if supported than the alpha particles would pass straight through. Found most of the alpha particles to pass straight through, some were slightly deflected, but others were completely deflected (unexpected).
Planetary model
Rutherford's model, electrons orbiting the dense and positive nucleus
electrons
__________ are found in the space around the nucleus
protium
a hydrogen isotope with 1 proton and 0 neutrons, written 1/1H, percent abundance 99.99
deuterium
a hydrogen isotope with 1 proton and 1 neutron, written 2/1H, around .01 percent abundance
tritium
a hydrogen isotope with 1 proton and 2 neutrons, written 3/1H, radioactive, percent abundance is less than .01
isotopes
all _____________ of an element are chemically identical (undergo the same chemical reactions)
empty space
atom is mostly ___________
ion
atom that has gained or lost one or more electrons, behave differently than neutral atoms, (ex: Na vs. Na+, one reacts with water, while the other dissolves)
amu
atomic mass units
isotope
atoms of the same element but have different mass numbers, when writing these the atomic number stays the same but the mass number changes. the amount of neutrons changes
Sir J. J. Thomson
by looking at angles of deflection with the Cathode Ray Tube, he calculated the charge to mass ratio of these particles by measuring the degree of deflection with different strength magnetic and electric fields. No matter which gas he used in the tube, the calculated charge to mass ratio of the particles was the same, he varied the gas and the electrodes but always got the same ratio
John Dalton
came up with the law of multiple proportions, developed a model on the atom based on already established laws: law of conservation of mass, definite proportions, multiple proportions.
Law of Conservation of mass
cannot create or destroy mass in a chemical reaction, ex: 2g hydrogen reacts with 16g oxygen to produce 18g water
Rutherford
concluded that all of an atom's positive charge and most of its mass is located in the center
Rutherford
concluded that most of the atom is empty space.
Lavoisier
considered the father of modern chemistry, developed the law of conservation of mass
Bercurial
credited with discovering radioactivity. used pitchblende, uranium, to find radioactivity, giving off particles without an external force (like the sun)
Cathode ray Deflecting Tube
demonstrates the influenece of a magnetic field to the electron beam. low pressure tube (with practically all gas sucked out of it). negative electrodes at one side, positive electrodes on the other, Sir William Crookes found a green glow.
Crookes
determined that the Cathode ray was made up of particles, not light
Milikan's Oil Drop Experiment
determined the charge of an electron. Given Thomson's charge to mass ratio calculation, the mass of an electron could then also be determined, oil drops were given a negative charge by attaching electrons to them. by balancing the force of gravity with the force from an electric field on these droplets, Millikan could determine the magnitude of the charge on each oil drop, and found the charge was always a multiple of 1.6 x10 ^-19 C.
Proust
developed the law of definite proportions
Sir William Crookes
did experiment with Cathode ray tube to find that there were negative particles.
Wilhelm Conrad Roentgen
discovered X rays by observing the fluorescence they produced
Thomson
discovered that all atoms had negatively charged subatomic particles
Chadwick
discovered the neutron in 1932, subatomic particle present in all atoms that has about the same mass as a proton but no electrical charge.
Law of Definite Proportions
elements combine in definite, fixed ratios by mass to form compounds. ex: water is always 1 gram of hydrogen for every 8 grams of oxygen, all the same ratio
Thomson's experiments
experiments with a cathode ray tube, tried to separate the charge from the particles by bending the rays with a magnet and then deflecting with electric plates. He could not separate the two. Tried to separate the negative charge from a particle by adjusting the electric field
Marie Curie
explained radioactivity, found radium and polonium
Dalton
explained the law of definite proportions by saying that atoms combine in small, whole number ratios to form compounds.
Democritus
first to propose that all matter is made up of atoms
protons
found in the nucleus, mass 1.672622 x 10 ^-24, relative mass: 1.007 amu
Crookes Maltese Cross Tube
glow passed through the tube to reflect a green +, the lines were straight, not fuzzy. shadow was perfect which meant there must be actual particles not just light
mass spectrum
graph that gives the relative mass and relative abundance of particle
Thomson's Plum Pudding Model
he thought that the atom was like a ball of positive charge with negative particles spread throughout, like raisins in plum pudding, all particles are identical in every atom, electrons in every atom, every atom has the same subatomic particles.
electrons
in an atom (not an ion) the number of protons is equal to the number of ___________
gamma, beta, alpha
list the three types of radiation from highest penetrating power to lowest penetrating power
Rutherford's Conclusions
majority of atom was empty space, particles went straight through, the positive charge and 99% of the atom's mass concentrated in a small volume in the center (discovery of the nucleus!) (dense and positive). electrons orbit around the nucleus. much smaller mass than the nucleus.
protons + neutrons
mass number
how nuclear symbols are written
mass number over atomic number next to the letter of the element
mass spectrometry
masses and abundances of isotopes are measured with a ________ __________, molecules into fragments are broken during the ionization process, these fragments can be used to help determine the structure of the molecule, their path is bent by a magnetic field, separating them by mass, similar to Thomson's Cathode Ray Experiment
electrons
negative electrical charge, mass of 9.109 x 10^-24, relative mass: .0005 u
anion
negative ion (gained electrons), written like C+, named by changing the ending of the name to ide, Ex: fluorine +1 electron = fluoride ion
neutrons
no electrical charge, mass: 1.674927 X 10 ^-24, relative mass : 1.009 u
problems with Rutherford's model
no nucleus, no electron shells
cation
positive ion (lost electrons), formed by metals, for each psotive charge the ion has 1 less electron than the neutral atom, keep the same names
nucleus
protons and neutrons are found in the _________
Scanning tunneling microscope
scientists used it by scannning the tip across a surface to create an image of atomic resolution, tunneling is exteremly sensitive to distance. The microscope not only allowed scientists to see the atoms on the surface, but they were able to move individual atoms across the surface.
Sir J. J. Thomson's hypothesis
since the beam came from the cathode (a negative electrode), and given how the ray is deflected by a magnet, the particles have a negative charge
Thomson
studied the effects of an electric field on the cathode ray
mole
the amount of substance that contains as many particles (atoms, molecules) as there are in 12.0 g of C-12
example of law of multiple proportions
water versus hydrogen peroxide: if 1g of hydrogen in each then 8g of oxygen in water to 16g of oxygen in hydrogen peroxide, gives a 1:2 ratio by mass of oxygen in the two compounds.
Cathode Ray Tube
the beam of a _________________ can be deflected by an electric field. Negatively charged electrons deflect the beam toward the positive field.
Thomson's conclusions
the cathode ray was made up of negatively charged particles, later called electrons, no matter what metal the electrodes were made up of, or what gas filled the tube, the same charge to mass ratio was calculated. All atoms have them, and they are identical in all atoms. He also thought atoms must have a positive componenet
relative atomic mass
the mass of one atom of an element relative to one atom of another element, defining one element against a standard.
Problems with Rutherford's model
the mass of the atom did not equal the mass of the positive charge alone. Why didn't the electrons fall into the nucleus? What keeps them in motion?
average atomic mass (or atomic weight)
the observed mass of an element is a weighted average of the masses of the naturally occuring atoms of that element.
percent abundance
the percentage of an element that is one isotope
radioactivity
the spontaneous disintegration of some elements into smaller pieces
Dalton
theorized that atoms are rearranged during chemical reactions
Rutherford
used alpha particles in his gold foil experiment
Democritus
went against Aristotle, who believed that matter was composed of four qualities, earth, fire, air, and water, ____________ believed all matter is composed of small, indivisible particles called "atoms"
Law of Multiple Proportions
when 2 or more elements combine to form different or multiple compounds, the ratio of the second element to a fixed mass of the first is always a small, whole number ratio.
mass number
when writing c-14, the 14 stands for the__________ _____
