Atom Flashcards
John Dalton- which theory?
put together many observations and results of numerous experiments made by other scientists and formulated the atomic theory.
Law of Conservation of Mass
(3)
“Atoms cannot be created or destroyed (postulate 1) or
converted into other types of atoms. (postulate 2)
since every atom has a fixed mass, (postulate 3) during a chemical reaction atoms are combined differently and therefore there is no mass change overall.”
Law of conservation of mass
Still has components of bothhhhh?????!????
matter as being composed of
small, indivisible
particles called atoms
atoms are like billiard balls, which are thought
to be
solid and indestructible ..dalton
they are in constant motion and collide with one
another, causing
changes in their motion and
resulting in chemical reactions
The billard ball model assumed that atoms were ?
indestructible, which was later disproved by the discovery of nuclear reactions, which can break atoms apart or merge them together to create new elements.
o The model did not account for the existence of ?, which were later discovered by scientists such as J.J. Thomson and Ernest Rutherford
of subatomic particles- electrons, protons, and neutrons,
did not explain the internal structure of atoms, which was later revealed by more advanced theories such as the atomic models of Niels Bohr and Erwin Schrödinger.
Billard ball
o The model did not account for the existence of isotopes- that are atoms of the same element but they have a different number of neutrons in their nuclei.
Billard ball
- Limitations of Dalton’s Model
- assumed that atoms were indestructible,
- did not account for the existence of subatomic particles- electrons, protons, and neutrons,
- did not explain the internal structure of atoms
- did not account for the existence of isotopes
- did not have any concept of chemical bonding, which is the way atoms combine to form molecules
- did not explain the phenomenon of atomic spectra, which was observed in light emitted or absorbed by atoms.
o He was able to explain some previously unexplained phenomena, such as the fact that atoms are electrically neutral, and that the ratio of the charge of an electron to its mass is the same for all elements.
J.J THOMSON
? discovered the electron, a subatomic particle while conducting experiments on ?
Thomson, cathode rays.
Thomson’s Plum
Pudding Modelsyays that?
Thomson’s Plum
o atoms are neutral because the negative charges of the electrons were balanced out by an equal amount of positive charge in the “soup” or “pudding”
Thomson’s Plum
Pudding Model weaknesses
did not account for the existence of the nucleus
could not explain the stability of atoms
ERNEST RUTHERFORD
proposed that atoms were composed of a small, dense, positively charged nucleus at the center, surrounded by negatively charged electrons that orbited around it like planets around the sun. ERNEST RUTHERFORD (1 ERNEST RUTHERFORD
The nucleus contains protons and neutrons, and the number of protons in the nucleus determines the element who?
ERNEST RUTHERFORD (
Discovered a particles where helium atom with their electrons are removed
Radioactivity
Model of an deho: atoms were composed of a small, dense, positively charged nucleus at the center, surrounded by negatively charged electrons that orbited around it like planets around the sun
Rutherford’s Planetary Model
Rutherford’s Planetary Model weakness
did not account for the fact that electrons move in multiple orbits around the nucleus
Niels bohr
NIELS BOHR proposed an early model of the atom as a central nucleus containing protons and neutrons being orbited by electrons in shells or energy levels
electrons orbit the nucleus in specific, discrete orbits, or “energy levels”, and that the energy of an electron is determined by its orbit
NIELS BOHR
these energy levels are designated by a number and the symbol “n“
Bohr’s Atomic Model
Bohrs atomic model weakness
failed to explain the electron-electron interactions in multi-electron atoms, which is important for chemical bonding
ERWIN SCHRODINGER
Quantum Mechanical Model” or the “Electron Cloud Model”
proposed the current model of the atom
ERWIN SCHRODINGER (19
Erwin describes the atom as a ?
small, dense nucleus containing protons and neutrons, surrounded by a cloud of electrons that occupy energy levels or “shells
describes the electron as a three- dimensional wave in the positively charged nucleus’ electronic field
Erwin
The Quantum Mechanical Model
describes the electron as a three- dimensional wave in the positively charged nucleus’ electronic field
An electron’s exact position and velocity (or momentum) cannot be determined at the same time. As a result, the electron’s path is only probable and not exact. This eventually resulted in the concept of ?.
atomic orbitals
o The probability of finding an electron at a point in an atom is proportional to the square of the ? i.e., [ψ]2. It is positive and is also known as a probability density. The value of [ψ]2 at various points within the atom can be used to predict the region around the nucleus where the electron will most likely be found or located.
wave function
Two important features of an atomic structure that are atoms consist of smaller particles called? And that some of these particles carry an electric charge. 
Subatomic particles
The charge-to-mass ratio was measured by
Sir Joseph John Thomson
charge-to-mass ratio of the particles in the cathode ray found to be ?? whatever metal was used as cathode or whatever gas present in the tube.
the same
These negatively charged particles, named “, were therefore considered to be present in all matter or a part of all atoms.
electrons
?
determined the charge of the electron through the
tamous?
Robert Andrews Millikan
(1868-1953)
‘oil-drop
experiment’.
He assumed that this smallest charge was the charge on one electron. This value is
1.60218 x
10-19 C (modern value).
evidence of the existence of protons was found by ?
(1850-1930) when he performed experiments using?
Eugene Goldstein
tubes containing gases at very low pressures and a tube with a perforated cathode.
How did he discover proton
He observed rays passing through the holes on cathode and moving away from the positive electrode which were positive particles left after the electrons had been removed from the atom.
Which atom has only one proton?
Hydrogen
Such nuclei also contain ?,
neutrons
Compare, neutrons, to protons (2)
Almost the same mass as the protons, but not electrically charged
The neutron was discovered in 1932 by
Sir James Chadwick
neutrons was in fact just slightly ? than the mass of the proton.
greater
The atom is an electrically ?, spherical entity composed of a positively charged central nucleus surrounded by one or more negatively charge electrons.
neutral,
C
The atomic ? consists of protons and neutrons.
nucleus
1 angstrom (A) =
1.0 x 10-10 m
In chemistry, it is common to use ? instead of grams to indicate the mass of the particles.
atomic mass unit (amu
An amu is equivalent to
1.66054 × 10-24 g.
Atomic no=
Proton
Atomic mass =
P+n
T or f
Two or more elements can have the same atomic number
Falls
Atoms of the same element which have different masses are called
We isotopes.
An atom
of a specitic isotope is called a
nuclide.
number of ? in an atom detines whar element the atom is
The number of
? in an atom defines the isotopes of an
element
Protons, neutrons
The
• number or ? in an atom defines what element the atom is. The number of ? in an atom defines the isotopes of an
element.
protons, neutrons
Because in the real world, all the elements exist as mixtures of
Isotope s
isotopes. Relative Atomic Mass (A) is calculated from the
isotopes of an element weighted by their relative abundances.
