Text A Chemistry 1.2 Developing Atomic Theories, Stopped At Page 20 Flashcards
What is the main function of a linear accelerator?
To fire fast-moving particles into a target surrounded by sensitive detectors
Linear accelerators help scientists probe inside tiny particles of matter by splitting them apart.
According to Dalton, what was the atom?
A solid, uniform sphere
Dalton’s view of the atom was foundational to early atomic theory.
During which centuries did scientists improve laboratory techniques for isolating pure substances?
1600s and 1700s
What did scientists observe consistently that led to the generalization of scientific laws?
An action or condition
Consistent observations led to the formulation of scientific laws.
What hypothesis was developed to explain several early scientific laws?
Matter is made up of tiny particles
Who was John Dalton?
An English scholar and teacher who published a comprehensive atomic theory in 1808
What was the heart of Dalton’s atomic theory?
Every substance is made up of indivisible atoms
What key difference did Dalton propose between atoms of different elements?
Their mass
What law did Dalton’s atomic theory help explain regarding mass during chemical reactions?
The total mass of substances before and after a reaction is always the same
This supports the idea that particles are rearranged but not created or destroyed.
List three key points of Dalton’s atomic theory.
- All matter is made up of small particles called atoms.
- Atoms cannot be created, destroyed, or divided into smaller particles.
- All atoms of the same element are identical in mass and size, but different from atoms of other elements.
True or False: Dalton’s theory stated that atoms of different elements are identical in mass and size.
False
What are compounds formed from?
Atoms of different elements combining in fixed proportions.
What do the tiniest particles of any compound contain?
The same types and relative numbers of atoms.
Do chemical reactions change the atoms themselves?
No, they change the way atoms are grouped.
What was a basis for many of Dalton’s conclusions?
Assumptions.
What was Dalton’s incorrect assumption about water?
That the formula for water was OH.
What did Joseph Proust’s measurements indicate about water?
It contains eight times more oxygen by mass than hydrogen.
What mass did Dalton assign to hydrogen?
One unit.
Based on Dalton’s assumption, what mass would an atom of oxygen have?
Eight units.
What did Dalton develop to track his assumptions about atoms?
A system of symbols.
What were some of Dalton’s inaccurate assumptions about compounds?
The composition of water and other compounds.
What did Dalton predict about nitrogen and oxygen?
There should be several different compounds, including NO, NO2, and NO3.
What technological achievement improved Dalton’s theory?
The refinement of the gas discharge tube.
What is a gas discharge tube?
A sealed glass vessel containing a gas at low pressure.
What are cathode rays?
Rays produced in gas discharge tubes when electricity flows through the gas.
Who improved the gas discharge tube in 1855?
Heinrich Geissler.
What is Daltonism?
Color-blindness, specifically to red.
What did ancient Greek philosophers speculate about the universe?
That it must be composed of small particles that could not be broken down.
What term did ancient Greek philosophers use to describe indivisible particles?
Atomos.
Did ancient Greek thinkers use experimental investigation to develop their ideas?
No.
True or False: Dalton’s predictions about compounds were later verified experimentally.
True.
Fill in the blank: Dalton’s calculations of relative masses were inaccurate due to _______.
Incorrect assumptions.
What did experiments with gas discharge tubes suggest about matter?
Matter contains tiny particles that have negative charges
This inference led to the discovery of electrons.
What was the scientific consensus at the end of the nineteenth century regarding Dalton’s atomic theory?
Many scientists were reluctant to abandon Dalton’s atomic theory
Dalton’s theory proposed that atoms are indivisible.
What did scientists not want to believe about Dalton’s indivisible atoms?
That they might actually be made up of even smaller particles
This reluctance hindered acceptance of the concept of subatomic particles.
True or False: The concept of electrons was widely accepted at the end of the nineteenth century.
False
Many scientists were hesitant to accept the existence of subatomic particles.
Fill in the blank: Experiments with gas discharge tubes led to the inference that matter contains tiny particles with _______.
negative charges
What did experiments with gas discharge tubes suggest about matter?
Matter contains tiny particles that have negative charges
This inference led to the discovery of electrons.
What was the scientific consensus at the end of the nineteenth century regarding Dalton’s atomic theory?
Many scientists were reluctant to abandon Dalton’s atomic theory
Dalton’s theory proposed that atoms are indivisible.
What did scientists not want to believe about Dalton’s indivisible atoms?
That they might actually be made up of even smaller particles
This reluctance hindered acceptance of the concept of subatomic particles.
True or False: The concept of electrons was widely accepted at the end of the nineteenth century.
False
Many scientists were hesitant to accept the existence of subatomic particles.
Fill in the blank: Experiments with gas discharge tubes led to the inference that matter contains tiny particles with _______.
negative charges
Who used a new version of the gas discharge tube in 1894 to provide evidence of cathode rays?
J. J. Thomson
What type of particles did J. J. Thomson demonstrate were present in cathode rays?
Negatively charged particles
What apparatus did Thomson modify to obtain evidence about cathode rays?
Gas discharge tube
What was the outcome of Thomson’s experiments regarding the relationship between charge and mass?
He found a quantitative relationship between charge and mass.
What are the negatively charged particles discovered by Thomson now known as?
Electrons
What is the mass of each electron compared to a hydrogen atom?
Less than the mass of a single hydrogen atom
What happens to cathode rays when a positively charged plate is placed near the tube?
The ray is attracted to the positive plate.
Fill in the blank: Thomson concluded that matter contained _______ charged particles.
negatively
Did J. J. Thomson initially have many believers in the existence of particles smaller than atoms?
No
What did Thomson say about a distinguished physicist’s reaction to his lecture on electrons?
He thought Thomson had been ‘pulling their legs.’
What does a ‘neon’ sign represent in terms of gas discharge tubes?
A modern version of a gas discharge tube
What determines the color of a neon sign?
The gas inside the tube
What color is emitted by a tube that contains neon gas?
Red
What gas glows violet-blue in a discharge tube?
Argon
When was the neon tube invented?
Not specified in the text
Where did the first neon sign appear?
Not specified in the text
Who is sometimes called ‘the father of the electron’?
J.J. Thomson
Thomson published results in 1897 referring to cathode ray particles as corpuscles.
What term did G. Johnstone Stoney invent in 1891?
Electron
He used it to describe a unit of charge in electrolysis experiments.
What did George Fitzgerald argue about electrons and corpuscles?
They were the same thing.
What is the charge of an electron?
Negatively charged.
What did scientists conclude about the presence of electrons?
Every atom contained electrons.
What must each atom contain to balance the negative charge of electrons?
A source of positive charge.
Who first suggested a model of the atom that included a positive charge cloud?
William Thomson (Lord Kelvin).
What is the Thomson model of the atom also known as?
Plum-pudding or raisin-bun theory.
What did Ernest Rutherford discover about radioactive elements?
They emitted three different types of emissions: alpha particles, electrons, and gamma rays.
Where did Ernest Rutherford teach from 1898 until 1907?
McGill University in Montreal.
What significant experiment did Rutherford conduct in 1909?
He probed the structure of atoms using alpha particles and gold foil.
What unexpected result did Rutherford observe in his gold foil experiment?
A small number of alpha particles bounced back from the gold foil.
Fill in the blank: The Thomson atomic model of 1903 viewed the atom as a positively charged sphere embedded with sufficient numbers of _______.
Electrons.
What did the Thomson model fail to account for?
The emission of alpha particles.
How much more massive are alpha particles compared to electrons?
About 7200 times.
What type of particles does polonium emit?
Alpha particles
Polonium is a radioactive element known for emitting alpha particles.
What happens to a fluorescent screen when struck by an alpha particle?
It lights up
Fluorescent screens are used in various experiments to detect alpha particles.
How do alpha particles interact with electrons in gold foil?
They are not significantly deflected
Alpha particles are much more massive than electrons, leading to minimal deflection.
What did Rutherford reason about the deflection of alpha particles?
Effects of many random deflections would cancel each other
This reasoning led to the conclusion that overall deflection would be minimal.
What did Rutherford’s observations lead him to develop?
A new atomic theory
This theory included both electrons and positively charged particles.
What did Rutherford conclude about the atoms in the foil?
They must possess something very dense and intensely positive
This conclusion was based on the observed rebounds of alpha particles.
What did most alpha particles do when passing through the gold foil?
Went straight through
This observation indicated that most of the positive alpha particles were not deflected.
What did Rutherford suggest about the ‘dense positive something’ in the atoms?
It must be relatively small
The small size was inferred because most alpha particles passed through the foil without deflection.
In what year did Hantaro Nagaoka propose an atomic model similar to Rutherford’s?
1904
Nagaoka’s model described a disk-shaped atom with negatively charged particles orbiting a positive nucleus.
What shape did Nagaoka’s atomic model describe?
Disk-shaped
This model depicted negatively charged particles orbiting a positively charged nucleus.
What did Rutherford note about his results regarding Nagaoka’s model?
They would be the same if Nagaoka’s model were correct
This indicates the compatibility of their models despite different descriptions.
What large region do atoms possess according to Rutherford’s theory?
A mostly empty space
This empty space is where electrons are thought to exist around the nucleus.
Fill in the blank: The _______ in the gold foil experiment were deflected off course.
Some alpha particles
This phenomenon indicated that certain alpha particles interacted with the dense positive center.
What is the central region of an atom called?
Nucleus
The nucleus is positively charged and contains almost all of the atom’s mass.
What particles are located in the outer region of the atom?
Electrons
Electrons have a single negative charge and are much less massive than protons and neutrons.
Who proposed the ‘solar-system’ atomic model in 1911?
Ernest Rutherford
Rutherford’s model visualized electrons moving around the nucleus similar to planets orbiting the Sun.
What is a proton?
A positively charged particle in the nucleus
A proton has about the same mass as 1836 electrons.
What is the term for atoms of the same element that differ in mass but are chemically alike?
Isotopes
Isotopes have the same number of protons but different numbers of neutrons.
What did Harriet Brooks discover about thorium?
It emits radioactive emissions that are actually a simpler atom, radon
Brooks was the first to recognize that one element could transmute into another.
What did Rutherford hypothesize about helium atoms?
They contain two protons and two neutrons
This would make helium four times as massive as hydrogen, which has one proton and one electron.
What is the volume of space surrounding the nucleus called?
Empty space
This space is large compared to the nucleus and contains the electrons.
True or False: Rutherford’s model suggested that atoms are packed closely together.
True
Rutherford assumed that atoms in the gold foil were closely packed, allowing most alpha particles to pass through.
Fill in the blank: The particle hypothesized by Rutherford that has no electrical charge is called a _______.
Neutron
The neutron is hypothesized to have the same mass as the proton.
What is the mass relationship between hydrogen and helium atoms according to Rutherford’s hypothesis?
Helium atoms are four times more massive than hydrogen atoms
This was explained by the presence of neutrons in helium.
What is the significance of Rutherford’s reasoning about the nucleus?
It showed that the nucleus is extremely small and dense
This contradicts Thomson’s idea of a cloud of positive charge.
What is the isotope of neon with 10 neutrons called?
neon-10
What is the isotope of neon with 12 neutrons called?
neon-12
How many protons do all neon atoms have?
10
What particle has no electric charge and was difficult to isolate?
neutron
Who provided experimental evidence for the existence of neutrons?
James Chadwick
What major objection was raised against Rutherford’s atomic model?
Electrons should emit energy and spiral into the nucleus
What is emitted by gases in a discharge tube when electrical energy is supplied?
light
What does the spectrum of light correspond to?
specific wavelengths
Who hypothesized that electrons have allowed energy levels?
Niels Bohr
What are the specific energy levels associated with electrons called?
electron shells
True or False: Electrons can exist between energy levels.
False
What happens when an electron absorbs energy?
It moves to a higher energy level
What happens when an electron emits energy?
It moves back to its original energy level
What shape do the energy levels of electrons have in three dimensions?
spherical shells
What are alpha particles now known to be?
helium nuclei
How many protons and neutrons are in an alpha particle?
2 protons and 2 neutrons
What was Niels Bohr a leading advocate for in later life?
international cooperation in peaceful uses of atomic energy
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