Chapter 7 Science Test Flashcards
How many elements were identified by the late 1700’s?
• More than 30 elements
Who proposed an atomic theory of matter?
• John Dalton in 1808
Who was the first person to envision the atom?
• Democritus
How did John Dalton envision the atom?
• A small smooth solid sphere without an electric charge
What was Dalton’s Theory?
• All matter is made of atoms, which are particles too
small to see
• Each element has its own kind of atom, with its own
particular mass
• All atoms of any one element are identical
• Compounds are created when atoms of different
elements combine in a specific ratio
• Atoms cannot be created, destroyed, or subdivided
during chemical changes
Who discovered what that led to changes in Dalton’s Theory?
• Michael Faraday showed that atoms could gain
electric charges
What Revisions were made to Dalton’s Theory?
• Matter must contain positive and negative charges
• Opposite charges attract, and like charges repel
• Atoms combine to form the particles of a compound
because of the electrical attractions between charged
atoms
When was the electron discovered, and who discovered it?
• The electron was discovered in 1898 by J.J Thomson
What was Thomson’s Revision to the Atomic Theory?
• Atoms contain electrons
• The electrons have a negative charge and a very small
mass
• The rest of the atom has a positive charge
• The electrons are embedded randomly in the positive
part of the atom
• Electrons can be removed from, or added to, atoms to
create charged atoms
What was Thomson’s model called?
• Raisin-bun model
How did Rutherford attempt to probe the structure of an atom?
• He bombarded a very thin piece of gold foil with small,
positively charged particles
• He expected most of the particles to be deflected, as
predicted by Thomson’s revision
What did Rutherford’s discovery lead to?
• Rutherford’s Nuclear model
What are Rutherford’s Revisions to the Atomic Theory?
• The nucleus contains all of the positive charge and
most of the mass of the atom
• The nucleus contains positively charged protons and
uncharged neutrons.
• Neutrons have the same mass as protons
• The nucleus is very small, compared with the size of
the atom
• The mass of an electron is 1/1800 the mass of a proton
• The size of the atom is determined by the size of the
orbit of the electron
• There is only empty space between the electrons and
the nucleus
Why did Rutherford know his theory was not completely correct?
• A well-established theory of electromagnetic waves
predicted that Rutherford’s orbiting electrons should
continuously emit energy, which they do not.
What happens when atoms absorb electrical or heat energy?
• They re-emit the energy as light
• Each element emits a very specific pattern of
wavelengths, or colours, of light, called the emission
spectrum
How did Niels Bohr solve the problems of Rutherford’s model of the atom?
• He used the emission spectrum of the element and
discoveries of other scientists.
What was Albert Einstein’s observation that Bohr used?
• Albert Einstein had shown that atoms can only absorb
or emit light energy in specific amounts
• Bohr used this to observation to explain why the
electrons orbiting the nucleus do not continuously give
of energy
What are electron shells?
• Specific orbits in which electrons circle the nucleus,
electrons cannot exist in between shells
How is the energy of a electron determined?
• Based on it’s distance from the nucleus
Why does each element have an unique pattern of light emission?
• Because its unique separation of its allowed electron
shells
When can atoms absorb or emit light energy?
• When they jump between shells
What are Bohr’s Revisions to the atomic Theory?
• Electrons are located in defined shells, which are
located certain distances from the nucleus
• Electrons cannot exist between the defined shells
• Electrons can gain energy to move up to a higher shel,
or they can lose energy to move down to a lower shell
• Electrons are more stable (have less energy) when
they are closer to the nucleus
