Honors Chemistry Chapter Four
How is atomic mass calculated?
(mass of isotope x % abundance) + (mass of isotope x % abundance)...
How did the contributions of Becquerel and the Curies contribute to the modern atomic theory?
-They discovered information about radiation. -Most atomic nuclei are stable, but a few aren't stable at all. These nuclei spontaneously emit particles that scientists refer to as radiation. -This helps with the modern atomic theory and how atoms work and are made.
What are the four parts of Dalton's Atomic Theory?
1. All elements are composed of tiny indivisible particles called atoms. 2. Atoms of the same element are identical. The atoms of any one element are different from those of any other element. 3. Atoms of different elements can physically mix together or can chemically combine in simple whole-number ratios to form compounds. 4. Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element, however, are never changed into atoms of another element as a result of a chemical reaction.
What contributions did the Curies make to science?
1. Curie Point 2. Curie's Law 3. Experimented with uranium and came up with the term radioactivity. 4. Discovered two new radioactive elements - polonium and radium.
Which parts of Dalton's Atomic Theory are still considered correct today?
1. No because atoms can be destroyed and divided via nuclear reactions. 2. No because isotopes have atoms with different masses. 3. No because atoms do not always combine in whole number ratios. 4. This is the only completely correct part.
What are the three subatomic particles?
1. Proton 2. Electron 3. Neutron
When did Henry Becquerel win the Nobel Prize?
1903
When did Marie Curie win the Nobel Prize?
1903
When did Pierre Curie win the Nobel Prize?
1903
When did JJ Thomson win the Nobel Prize?
1906
When did Ernest Rutherford win the Nobel Prize?
1908
When did Niehls Bohr win the Nobel Peace Prize?
1922
When did Robert Millikan win the Nobel Prize?
1923
When did James Chadwick win the Nobel Prize?
1935.
How do you get the number of neutrons from a nuclear symbol?
A - Z = Number of Neutrons
In a nuclear symbol, for what does a stand?
A = Mass Number (Number of Protons and Neutrons)
What is a nuclear reaction?
A change that occurs in the nucleus of an atom that changes the composition of the nucleus.
What are cathode rays?
A stream of electrons emitted by the cathode in electrical discharge tubes.
What is the mass of a neutron?
About 1 x 10⁻²⁷
What is the mass of a proton?
About 1 x 10⁻²⁷
What is the mass of an electron?
About 9 x 10⁻³¹
Who were the alchemists?
Alchemists were philosophers who tried to transmute baser metals into more precious metals like gold.
What was Democritus's major contribution?
All materials are composed of indivisible atoms.
All nuclei with more than ____ protons (an atomic number greater than ____) are radioactive.
All nuclei with more than *83* protons (an atomic number greater than *83*) are radioactive.
In terms of speed, list the types of radioactive decay in order from low to high.
Alpha, Beta, Gamma
What are the products of a nuclear reaction?
Alpha, beta, and gamma radiation.
What is an atom?
An atom is the smallest particle of an element that retains its identity in a chemical reaction. All matter is composed of atoms. They are the basic building blocks of matter. Atoms come together to make molecules.
What are ions?
An electrically charged atom or group of atoms formed by the loss or gain of one or more electrons.
What do beta rays give off?
An electron (⁰₋₁ e).
Describe Bohr's model of the atom.
An electron is found only in specific circular paths, or orbits, around the nucleus. Each possible electron orbit in Bohr's model has a fixed energy called energy levels. Each energy level can hold a specific number of electrons.
What is a radioactive isotope?
Any of several species of the same chemical element whose nuclei are unstable and dissipate excess energy by spontaneously emitting rays of radiation in the form of alpha, beta, and gamma rays.
What was significant about Dalton's Atomic Theory vs. Democritus or Aristotle?
Aristotle thought that all materials on the earth were made up of the four elements. He did not believe in atoms. Democritus believed that all materials on earth were made up of extremely small, indestructible atoms and that a group of atoms formed multiple different elements. Aristotle's theory was thought true until disproved by John Dalton when he proved Democritus's theory. Antoine Lavosier took Dalton's proven theory and applied it when making the Law of Conservation of Matter.
Why was Aristotle considered correct over Democritus based on the time period?
Aristotle was the tutor of Alexander the Great and people in general found him more credible, plus Democritus had no evidence to support his ideas.
In the cathode ray experiment, why did the rays bend toward the positive plate?
Because the current produced by the generator is negatively charged and opposites attract.
Because they have different numbers of neutrons, isotopes differ in ____ but not in ____.
Because they have different numbers of neutrons, isotopes differ in *relative atomic mass* but not in *chemical properties*.
What was JJ Thomson's major contribution?
Cathode Ray Experiment
What was Dalton's major contribution?
Dalton's Atomic Theory.
What did Democritus say about matter? When? What did he call those particles?
Democritus was a Greek philosopher who said that all materials were composed of small indivisible particles called atomos. The lack of experimental evidence prevented clear resolution of this debate regarding the true nature of substances. This was proposed from 460-370 BC.
Why is Bohr's model of the atom sometimes called the planetary model?
Electrons are in orbit around the nucleus just like the planets are in orbit around the sun.
What contributions to science did alchemists make?
Even though the alchemists were wrong, alchemy led to chemistry.
Of what four substances did Greeks believe matter was made?
Fire, Earth, Water, and Air. They did not have clear evidence, though, so it was not clear whether this was true or not.
What did Aristotle believe about the atom?
He believed that fire, earth, water, and air made up matter and that no matter how many times you cut a form of matter in half, you would always have a smaller piece of that matter.
Describe Robert Millikan's Oil Drop Experiment.
He charged oil drops with a battery to find the charge and mass of an electron.
Describe Thomson's Plum Pudding Model of the atom.
He created it after he discovered electrons. It represents the positive and negative charges in an atom - the positive and negative balance each other out. Thomson saw the atom as a large positively charged mass with random negatively charged particles distributed through it, like oatmeal with raisins or a chocolate chip cookie.
What was Pierre Curie's major contribution?
He discovered information about radiation with Marie Curie.
What was James Chadwick's major contribution?
He discovered neutrons.
What did Henri Becquerel discover?
He discovered radioactivity, though he thought it was a spontaneous emission by the uranium.
What was Henri Becquerel's major contribution?
He discovered radioactivity.
What did Robert Millikan discover about the electron?
He discovered than an electron carries one unit of negative charge and its mass is 1/1840 the mass of hydrogen.
What was Ernest Rutherford's major contribution?
He discovered the nucleus.
What did Rutherford hypothesize would occur in his gold foil experiment?
He hypothesized that if the current atomic model was correct, the beam of alpha particles would directly pass through the sheet of gold in a straight line.
What else did Thomson do?
He introduced the idea of subatomic particles.
What was Niehls Bohr's major contribution?
He investigated the structure of atoms and the radiation emanating from them.
What was Aristotle's major contribution?
He thought matter could always be divided.
Beta rays can be stopped by ____.
Heavy clothing
What are alpha particles?
Helium atoms that lose their two electrons.
What do gamma rays give off?
High energy (so no mass and no change in protons) (⁰₀γ (it's the little upside down fish thing)).
Describe Ernest Rutherford's Gold Foil Experiment.
His plan was to shoot a beam of alpha particles through a thin sheet of gold. A zinc sulfide screen was placed around the foil as a backdrop upon which the alpha particles would appear. It had to be performed in complete darkness so the particles could be seen.
In a nuclear symbol, the ____ numbers are always on top and they are both ____ (no ____).
In a nuclear symbol, the *larger* numbers are always on top and they are both *integers* (no *decimals*).
Where are neutrons found in the atom?
In the nucleus.
Where are protons found in the atom?
In the nucleus.
Gamma rays can be stopped by ____.
Lead (some still make it through, but only a fraction of the original amount)
What is the law of electrostatics in the atom?
Like charges of electricity repel each other, whereas unlike charges attract each other. When you look at a periodic table, every element is electrically neutral because the protons and electrons are equal, so they balance each other out.
How can you tell which is the atomic mass and which is the mass number when given a number?
Mass number is always a whole number, where atomic masses can be written in decimals.
Explain the Law of Conservation of Matter as explained by Antoine Lavoisier.
Matter is neither created nor destroyed because the atoms are not created nor destroyed during a chemical reaction. This law allows scientists to check for human error in a chemical reaction by checking if the mass of the product equals the mass of the reactants.
What is the charge of an electron?
Negative
What is an anion?
Negative ion created by an electron gain and attracted to the anode.
What particle did Thomson discover? What did he call it? What do we call it today?
Negatively charged particles. Corpuscles. Electrons
Which subatomic particle did James Chadwick discover?
Neutron
When did Aristotle win the Nobel Prize?
Never
When did Dalton win the Nobel Prize?
Never.
When did Democritus win the Nobel Prize?
Never.
What is the charge of a neutron?
No charge.
Do electrons have a circular orbit?
Not necessarily, but they do follow a certain path.
Alpha rays can be stopped by ____.
Paper
What is the charge of a proton?
Positive
What is a cation?
Positive ion created by electron loss and attracted to the cathode in electrolysis.
What were Rutherford's results in the gold foil experiment? How did they change the appearance of the atomic model?
Results: Most alpha particles passed through, but some deflected to the outside ring (the zinc sulfide screen). This confirmed that the atom contained more than empty space and scattered electrons (he discovered the nucleus). It disproved the previous theory. Model: The new model contained positively charged material in the center of the atom, which would be named the nucleus.
What was Marie Curie's major contribution?
She discovered information about radiation with Pierre Curie and discovered 2 new elements polonium and radium.
What are cathodes?
Sources of electrons in an electric device. (negatively charged)
What are anodes?
Sources of protons in an electric device. (positive electric charge)
What was Robert Millikan's major contribution?
The Oil Drop Experiment.
What is atomic mass?
The average mass of all atoms in an element.
What do alpha rays give off?
The equivalent of 1 Helium 4 nuclei (⁴₂ He).
Explain the Law of Constant Composition as explained by Joseph Proust.
The law of constant composition says that, in any particular chemical compound, all samples of that compound will be made up of the same elements in the same proportion or ratio.
What is radioactive decay?
The natural process in which an atom of a radioactive isotope will spontaneously decay into another element through one of three common processes: alpha decay, beta decay, and gamma decay.
The neutron has the same ____ as the proton, but has no ____, making it ____. It is present in all atoms except for ____. It is found in the ____ with the ____, and the ____ circle around them, but this wasn't discovered until after ____.
The neutron has the same *mass* as the proton, but has no *electric charge*, making it *neutral*. It is present in all atoms except for *hydrogen*. It is found in the *nucleus* with the *protons*, and the *electrons* circle around them, but this wasn't discovered until after *Rutherford*.
Why do electrons orbit around the nucleus?
The nucleus has a positive charge and electrons have a negative charge, and in chemistry, opposites attract.
What is mass number?
The number of protons and neutrons.
What is relative abundance?
The percentage of that particular isotope that occurs in nature. It can only be calculated when an element has only two isotopes.
What is the difference between saying atomic mass and average atomic mass?
There is none - atomic mass is always an average because it is the average of all the isotopes.
Where are electrons found in the atom?
They are found outside of the nucleus in fixed energy levels according to Bohr's model.
What are isotopes?
Two or more forms of an element that have the same number of protons but a different number of neutrons in their nuclei.
What is electrolysis?
When you put an electric current through something.
Describe JJ Thomson's Cathode Ray Experiment.
Without Thomson's Cathode Ray Experiment, we would not have been able to invent things like big screen TVs and neon signs. Through his experiment, it was found that atoms are further divisible and that an electron was one of the fundamental units of an atom.
In a nuclear symbol, for what does x stand?
X = Element Symbol
What is meant by a nuclear symbol?
XAZ Method Y \ / Z / \ (X with a superscript Y and a subscript Z)
In a nuclear symbol, for what does z stand?
Z = Atomic Number (Number of Protons)
How do you calculate relative abundance?
amu1 (x) + amu2 (1-x) = average atomic mass x = decimal abundance (move decimal point to turn into percent - that's your relative abundance)
amu
atomic mass unit
