Unit 3: Atomic THeory Flashcards
which greek philosopher believed in atoms and which philosophers believed that matter is continuous?
Democritus
Aristotle and Plato
What four elements did the ancient greeks think matter was composed of?
Earth, Air, Water, Fire
John Dalton
An english chemist who in 1803 offered ideas about atoms in five statements, combined into Dalton’s Atomic Theory
By when was it accepted that two elements could combine to form a compound, and that pure samples would always have the same composition by mass?
1803
What is the first statement of Dalton’s Atomic Theory?
Matter is composed of extremely small particles called atoms.
Second statement of Dalton’s Atomic Theory?
Atoms of a given element are the same (identical), but different elements have different atoms.
Third statement of Dalton’s Atomic Theory?
Atoms cannot be subdivided, created or destroyed.
Fourth statement of Dalton’s Atomic Theory?
Atoms can combine to form compounds in simple whole number ratios.
Fifth statement of Dalton’s Atomic Theory?
In chemical reactions, atoms are combined, separated, or arranged.
Law of Multiple Proportions
Single whole number ratios that compounds are composed of.
why the 1800s they’d demonstrated that matter also had an…
electrical nature
what did benjamin franklin say about electricity?
that electricity is related to tiny, negatively charged particles
what were electrons named after?
greek word ‘elektron’ meaning amber
atoms are electrically
neutral
when did JJ Thomson experiment with cathode ray tubes?
1897
what was the first discovery of a subatomic particle
jj thomson’s experiments with cathode rays, which he concluded were a stream of negatively charged particles
what did jj thomson (confirmed by rober millikan) demonstrate with his experiments about the electron?
that an electron’s volume was very small in relation to it’s mass
the cathode rays were determined to behave like…
particles
what are the two conclusions made from the thomson cathode experiments?
1) If atoms are electrically neutral there must be a positively charged particle within the atom
2) if atoms have a mass there must be other particles within the atom which contain most of the mass.
what was thomson’s model of the atom called?
plum pudding model
when did rutherford do his gold foil experiment?
1911
explain the gold foil experiment
positive alpha particles were used to bombard a thin piece of gold foil with positively charged alpha particles
what did rutherford expect, if mass and charge were uniformly distributed throughout an atom?
that the alpha particles would pass through with a slight deflection.
conclusions of the gold foil experiment
- most of the atom is empty space
- the atom contains a small dense positive center (the nucleus)
- electrons surrounding the nucleus orbit in a planetary fashion, proposing a planetary model.
results of the gold foil experiment
- most particles passed through Au foil, since atoms are made up mostly of empty space
- very few particles were deflected back towards the source of the alpha particles.
who discovered the neutron?
james chadwick
when and how did chadwick discover the neutron?
in 1932, when he bombarded Be atoms with alpha particles and they emitted an energetic stream of radiation.
why did it take so long for the neutron to be discovered?
- it is neutral, so no charge
- difficult time, the great depression
describe Neils Bohr’s model of the atom
- it placed each electron in a specific energy level
- electrons moved in definite orbits around the nucleus like planets
- these orbits/energy levels are located at certain distances from the nucleus
when did Neils Bohr create his model?
1913
bohr: lowest energy level is closest
to the nucleus
bohr: electrons can move between
energy levels
bohr. electrons will never be found
between levels
what is the modern model of the atom?
the wave-mechanical model
when did schrodinger propose his theories?
1926
background of the wave-mechanical model
in 1926 schrodinger proposed that
- electrons have a dual wave-particle nature - electrons do no travel in orbits around the nucleus based on QUANTUM MECHANICS
electrons exist in a…
three-dimensional region around the nucleus, with an orbital being the “probable” location of an electron.
wave-mechanical model AKA
an electron cloud
what is the probable location of an electron based on?
how much energy the electron has
the most dense area in the wave model…
is where the most probability of finding an electron lies
timeline of atomic theory: 6 dates
- greek model in 400 BC
- dalton model in 1803
- thomson model in 1897
- rutherford model in 1911
- bohr model in 1913
- wave model (modern) in 1926
- james chadwick neutron 1932
list the masses of a proton, neutron, and electron
1 amu, 1 amu, and 1/1836 amu (0 in notation)
describe symbol for subatomic particles
(before letter) superscript mass, subscript charge, letter (p, n, or e-)
what does amu stand for and who defined it?
atomic mass unit, john dalton
1 amu = ____ mass of carbon-12 atom
1/12 of the mass
1 C-12 atom =
12 amu
ions
charged particles created by the gaining or losing of electrons
all metals ___ electrons, therefore…
lose, therefore they always become positive ions
nucleons
protons and neutrons, found in the nucleus
sum of the nucleons =
the mass of the nucleus
Isotope
Atoms of the same element that have different mass numbers,
What are the three isotopes of Hydrogen
Protium, deuterium, and tritium
What is another name for heavy water?
Deuterium
Nuclide
Term for any isotope
Name the number of protons and neutrons for protium, deuterium, and tritium.
Protium: 1, 0
Deuterium: 1, 1
Tritium: 1, 2
What isotope of hydrogen makes up 99.985% of the hydrogen on earth? 0.015%? Trace amounts?
Protium, deuterium, tritium
Average atomic mass
The atomic mass is the average mass of all naturally occurring isotopes.
How do you calculate the atomic mass/average atomic mass?
Take the percent abundance (as a decimal), multiply that by the mass number of the isotope, and divide this by 100.
Do this for all isotopes
Add up the products.
Mass spectrometer
Used to detect isotopes by shooting an ion beam through a magnet that separates the lighter atoms from the heavier ones, which then are shot toward ion detectors.
Neils Bohr model: electrons are attracted to a positive nucleus but…
remain in orbit which revolve around a center nucleus.
Orbits(shells) are also called
Principal Energy Levels (PELs)
According to Bohr’s model, what are the only regions in which electrons can be found ?
PELs
What are the five points of Bohr’s atomic theory?
- Electrons are located in energy levels outside the nucleus.
- No change in energy when electron is in an energy level.
- Ground state is when the electron is it the lowest possible energy state that it is stable in.
- Change in energy occurs when the electron changes energy levels.
- E- absorb energy to move to a higher energy level as release energy to move to a lower one.
Ionization energy
Lowest amount of energy needed to remove an electron from an atom.
Name the max # of electrons for the first 4 PELs
2, 8, (for first 20 elements)8 (21 and up) 18, 32
One orbital can hold up to _____ electrons and must be going in _____ directions
2 electrons, opposite
what did bohr not know?
He didn’t know why only certain energies were allowed, and called these allowed energies Energy Levels.
an electron will only absorb
as much energy as needed to move to a certain level
what are the four quantum numbers
n, l, m sub l , m sub s
what do each of the four quantum numbers stand for
in order: energy level, shape, orientation, and spin direction
what range is accepted in ‘shape’ to represent different sublevels?
0(s), 1 (p), 2(d), 3(f)
quantum mechanical model: (4 points)
- in each energy level e- occupy sublevels/atomic orbitals
- principal quantum number = number of energy sublevels
- sublevels are s, p, d, f
- they have different shapes, s = spherical, p = dumbbell, d and f are very complex.
Principal QN is related to
the size and energy of the orbital
Angular momentum QN
relates to the shape of the orbital (0,1,2,3) (l)
Magnetic QN
relates to the orientation of the orbital in space relative to other orbitals
Electron spin QN
relates to the spin states of the electrons. The spinning creates a magnetic field.
what block is the s block on the periodic table?
the first two groups
what block is the p group
last 6 groups
what block is the d group
transition metals
what is the f block?
lanthanides and actinides
