Atomic Theory Flashcards
Guiding Questions
What are the parts that make up an atom?
What is atomic theory?
What evidence supports the modern model of the atom?
Atom
A particle of matter that uniquely defines a chemical element
Electron
A stable subatomic particle with a charge of negative electricity, found in all atoms and acting as the primary carrier of electricity in solids
Nucleus
The central and most important part of an object, movement, or group, forming the basis for its activity and growth
Proton
A stable subatomic particle occurring in all atomic nuclei, with a positive electric charge equal in magnitude to that of an electron, but of opposite sign
Neutron
A subatomic particle of about the same mass as a proton but without an electric charge, present in all atomic nuclei except those of ordinary hydrogen
Atomic Number
The number of protons in the nucleus of an atom, which determines the chemical properties of an element and its place in the periodic table
Isotope
Each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties; in particular, a radioactive form of an element
Mass Number
The total number of protons and neutrons in a nucleus
Nanowhiskers
tiny threads of carbon or silver that measure about 10 nanometers (1nm = 0.000000001m)
What do nanowhiskers have to do with atoms?
Both atoms and nanowhiskers are so small it’s hard to imagine, yet nanowhiskers are still 10x bigger than atoms
Scientists have always tried to find the smallest bits of matter that exist
Now they know that even atoms themselves are constructed from smaller particles
What is an atom?
An atom is the smallest particle that still can be considered an element
Why are atoms so difficult to study?
Because they’re so tiny
When did atomic theory start to grow
Atomic Theory began to grow in the 1600s as more scientists began to experiment with atoms
Who was John Dalton?
John Dalton, an English chemist, created his own theory which became very popular
Dalton’s Atomic Theory
- All elements consist of atoms that cannot be divided.
- All atoms of the same element are exactly alike and have the same mass. Atoms of
different elements are different and have different masses. - An atom of one element cannot be changed into an atom of a different element by a
chemical reaction. - Compounds are formed when atoms of more than one element combine in a specific
ratio.
Why might a theory change over time?
New evidence and perspective emerges
What major change was made to Dalton’s theory?
Part two of Dalton’s theory had to be modified after mass spectrometry experiments demonstrated that atoms of the same element can have different masses because the number of neutrons can vary for different isotopes of the same element
Thomson’s atomic model
Discovered that atoms contain negatively charged particles (electrons). Also reasoned atoms must contain some sort of positive charge (protons).
Rutherford’s atomic model
Using his model, concluded that the atom is mostly empty space but has a dense, positive charge at its center.
Bohr’s atomic model
Suggested that electrons move only in specific orbits around an atom’s nucleus
(like a solar system).
Cloud’s atomic model
Came about in the 1920s and proved Bohr’s theory wrong. Instead electrons
move rapidly within a cloud-like region around the nucleus.
How do later atomic theories differ from Dalton’s atomic theory?
Dalton says atoms of different elements differ in size and mass, whereas the modern theory says they differ in average mass
In 1932, which English scientist proved that neutrons exist in the nucleus of an atom.
James Chadwick
Neutrons, protons, and electrons are known as what?
Subatomic particles
A subatomic particle is…
Any particle smaller than an atom.
Most of an atom is made up of space in which the electrons move…
This space is huge compared to the space in which the nucleus occupies
Protons
+1
Electrons
-1
Neutrons
0
If there’s more protons
The atom is positive
If there’s more electrons
The atom is negative
If there’s equal parts protons and electrons
The atom is neutral
When it comes to the masses of particles…
Protons and neutrons are about equal
Electrons
Are much smaller
It takes about 1,840 electrons to equal
The mass of one proton or neutron
Scientists normally measure atoms using
Atomic mass units
What can atoms tell us about elements?
The number of protons in the nucleus of an atom is the atomic number of that atom’s element
The definition of an element is based
On its atomic number
Every oxygen atom has 8 protons, so…
The atomic number of oxygen is 8
Atoms with the same number of protons and different number of neutrons are called
Isotopes
An isotope is identified by its mass number
Which is the sum of the protons and neutrons in the atom
The most common isotope of oxygen has a mass number of
16
Why do you think the mass number only includes the numbers of protons and neutrons?
The mass of the electrons is too small to affect the overall mass
