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__________ _____