The Atomic Model Quiz
Neutral atom
# of protons = # of electrons
Cathode ray experiment
-Cathode ray tubes are sealed glass tubes from which most of the air has been evacuated. -A high voltage is applied across two electrodes at one end of the tube, which causes a beam of particles to flow from the cathode (the negatively-charged electrode) to the anode (the positively-charged electrode). -Thomson placed two oppositely-charged electric plates around the cathode ray. The cathode ray was deflected away from the negatively-charged electric plate and towards the positively-charged plate (This indicated that the cathode ray was composed of negatively-charged particles) Conclusions: 1. The cathode ray is composed of negatively-charged particles. 2. The particles must exist as part of the atom, since the mass of each particle is only 1/2000 the mass of a hydrogen atom. 3. These subatomic particles can be found within atoms of all elements.
Nucleus
-Center of an atom held together by nuclear forces (both strong + weak) -Makes up most of atom's mass -Contains protons and neutrons -Size: 1x10^(-15) meter
Democritus
-Greek philosopher that developed a new theory of matter (400 B.C.) : that said atoms are the basic, building block of matter -believed: atoms are tiny, indivisible, indestructible, solid particles that are surrounded by empty space and constantly moving at random. -based his ideas on reasoning rather than science; he knew that if you took a stone and cut it in half, each half had the same properties as the original stone. He reasoned that if you continued to cut the stone into smaller and smaller pieces, at some point you would reach a piece so tiny that it could no longer be divided. -He called these infinitesimally small pieces of matter atomos, meaning "indivisible." -his atomic model was solid and homogenous. -stated all atoms differ in size, shape, mass, position and arrangement, with a void exists between them.
Ernest Rutherford
-Nuclear model of the atom (1911) -studied under thomson -Gold foil experiment: he fired positively charged alpha particles at a thin sheet of gold foil. Most passed through with little deflection, but some deflected at large angles. This was only possible is the atom was mostly empty space, with the positive charge concentrated in the center: the NUCLEUS. -Model shows that an atom is mostly empty space, with electrons orbiting a fixed, positively charged nucleus in set, predictable paths
Niels Bohr planetary model
-Planetary model (1913) -he modified Rutherford's model of the atom by stating that electrons moved around the nucleus in orbits of fixed sizes and energies. Electron energy in this model was quantized; electrons couldn't occupy values of energy between the fixed energy levels. 1. Electrons occupy only certain orbits around the nucleus. Those orbits are stable and are called "stationary" orbits. 2. Each orbit has an energy associated with it. The orbit nearest the nucleus has an energy of E1, the next orbit E2, etc. 3. Energy is absorbed when an electron jumps from a lower orbit to a higher one and energy is emitted when an electron falls from a higher orbit to a lower orbit. 4. The energy and frequency of light emitted or absorbed can be calculated by using the difference between the two orbital energies.
JJ Thomson
-Plum pudding model (1904) -discovered electron through experiments with cathode ray tubes; showed that all atoms contain tiny negatively charged subatomic particles, or electrons, and were scattered throughout a spherical cloud of positive charge.
James Chadwick
-Proved the existence of neutrons and Rutherford's atomic theory (1932) -Bombarded beryllium atoms with alpha particles, creating an unknown radiation -interpreted unknown radiation as a "neutral particle" (neutron) -Model with nucleus made of protons and neutrons in the middle, with electrons orbiting.
atomic number
-number of protons in the nucleus of an element -DEFINES the element
Erwin Schrodinger
-quantum model (1926) -Stated that electrons do not move in set paths around the nucleus, but in waves in a cloud where their position is uncertain -Unlike the Bohr model, the quantum mechanical model does not define the exact path of an electron, but rather, predicts the odds of the location of the electron. -This model can be portrayed as a nucleus surrounded by an electron cloud. Where the cloud is most dense, the probability of finding the electron is greatest, and conversely, the electron is less likely to be in a less dense area of the cloud.
ion
A charged atom
anion
A negatively charged ion -atoms have gained e-, so there are more electrons than protons
cation
A positively charged ion -Atoms have lost e-, so there are more protons than electrons
excited state
A state in which an atom has a higher potential energy than it has in its ground state -light or energy is emitted when the electron falls back down to its ground state or lower level. -the change in energy relates directly to the color of light or part of the electromagnetic spectrum
electron
A subatomic particle that has a negative charge -mass: 1x10^(-31) kg
proton
A subatomic particle that has a positive charge and that is found in the nucleus of an atom -mass: 1.6x10^(-27) kg
neutron
A subatomic particle that has no charge and that is found in the nucleus of an atom -mass: 1.6x10^(-27) kg
Electromagnetic spectrum
All of the frequencies or wavelengths of electromagnetic radiation -Low energy and low frequency is associated with long wavelength (radio waves) -high energy and high frequency is associated with short wavelength (gamma rays)
isotopes
Atoms of the same element (same number of protons) that have different numbers of neutrons -differ in mass number
Atom
Basic unit of matter -size: 1x10^(-10) m -mostly empty space
visible light
Electromagnetic radiation that can be seen with the unaided eye -red 625-740 nm -orange 590-625 nm -yellow 565-590 nm -green 520-565 nm -cyan 500-520 nm -blue 435-500 nm -violet 380-435 nm the light the e- emits corresponds to the EM spectrum
John Dalton
English chemist and physicist who formulated the modern atomic theory -Solid sphere model of the atom (1803) -Formulated the first modern description of the atom as the fundamental building block of all chemical structures. 1. All matter is made of indivisible particles called atoms, which cannot be created or destroyed. 2. Atoms of the same element have identical mass and physical properties. 3. Compounds are combinations of atoms of 2 or more elements. 4. All chemical reactions involve the rearrangement of atoms.
Max Planck
German physicist who developed quantum theory -believed that particles can exist only at specific amounts of energy or quanta
Gold Foil Experiment
In his famous gold foil experiment, Rutherford fired a thin beam of alpha particles at a very thin sheet of pure gold. -Alpha particles are helium nuclei and they are given off in various radioactive decay processes. -In this case, Rutherford placed a sample of radium (a radioactive metal) inside a lead box with a small pinhole in it. Most of the radiation was absorbed by the lead, but a thin beam of alpha particles escaped out of the pinhole in the direction of the gold foil. -The gold foil was surrounded by a detector screen that would flash when hit with an alpha particle. -Based on Thomson's plum pudding model, Rutherford predicted that most of the alpha particles would pass straight through the gold foil because the positively charged "soup" would be too weak to affect the path of the particles -The positive charge must be localized over a very tiny volume of the atom, which also contains most of the atom's mass, explaining why a very small fraction of the alpha particles were deflected drastically, due to the rare collision with a gold nucleus. -Since most alpha particles passed straight through, the atom must be made up of mostly empty space.
emission spectra
The emission lines correspond to photons of discrete energies that are emitted when excited atomic states in the gas make transitions back to lower-lying levels.
Beryllium Experiment
Until 1932, the atom was believed to be composed of a positively charged nucleus surrounded by negatively charged electrons. In 1932, James Chadwick bombarded beryllium atoms with alpha particles. An unknown radiation was produced. Chadwick interpreted this radiation as being composed of particles with a neutral electrical charge and the approximate mass of a proton. This particle became known as the neutron. With the discovery of the neutron, an adequate model of the atom became available to chemists.
average (relative) atomic mass
Weighted average of all the mass numbers of all the isotopes of an element avg atomic mass = (mass1 x abundance1) + (mass2 x abundance 2)+...
Bohr's model debunked
What we don't believe -electrons travel in fixed orbits What we still believe -Electrons are associated with specific amounts of energy or energy levels (the energy is quantized) -electrons can "jump" to other energy levels, but they cannot exist between energy levels
electron cloud
a region around the nucleus of an atom where electrons are likely to be found
amu
atomic mass unit -decimal numbers that usually round up to an isotope's mass number
electron excitation
movement of an electron to a higher energy state from the ground state
isotopic notation
notation that shows the chemical symbol, atomic number, and mass number for an isotope of an element -charge can be shown in the upper right (ex. 2-, -, or 3+)
ground state
the lowest allowable energy state of an atom
mass number
the sum of the number of neutrons and protons in an atomic nucleus -for one atom
