Chemistry 3.1-3.2
Why did Rutherford choose alpha particles (helium nucleus) for his Experiment?
They were small and positively charged, so Rutherford thought they would pass through the malleable gold
2H₂ + O₂ --> 2H₂O What parts of Dalton's atomic theory are illustrated by this reaction? What law does this reaction illustrate?
- Atoms cannot be created, subdivided, or destroyed. - Atoms of different elements combine in simple, whole-number ratios to form compounds - the law of conservation of Mass
An aluminum isotope contains of 13 protons, 13 electrons, and 14 neutrons. It's mass number is
27
How many grams of hydrogen (H2) must combine with 32g oxygen (O₂) to produce 36 g of hydrogen peroxide according to the equations: H₂ + O₂ --> H₂O₂. What law does this demonstrate?
4g. The Law of conservation of mass
Why did Rutherford choose Gold for his experiment?
Gold is very malleable, and he could roll it into sheets thin enough for the alpha particles to pass through.
the law of definite proportions
a chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound
What did Rutherford conclude about the structure of the atom?
an atom contains a small, dense, positively charged central region
The smallest unit of an element that can exist wither alone or in molecules containing the same or different elements is the _____
atom
In cathode-ray tubes, the cathode ray is emitted from the negative electrode, which is called the _______.
cathode
In the cathode ray tube, the negative electrode is called the _________.
cathode
Aristotle believed matter was...
continuous (not made of particles), (infinitely divisible)
According to Rutherford's experiment, the atom is composed largely of...
empty space
In Rutherford's experiment, most alpha particles passed through the atoms undeflected because most of the atom is _________.
empty space
What direction do the cathode rays move when no electric field is applied?
from the negative metal electrode to the positive metal electrode
the law of multiple proportions
if two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers
the law of conservation of mass
mass is neither created nor destroyed during ordinary chemical reactions or physical changes
_________ forces are short range forces that bind protons and neutrons together.
nuclear
Most of the atom's mass is in it's _________.
nucleus
The gold foil experiment lead to the discovery of the
nucleus
Location, relative mass, and charge of a neutron:
nucleus, 1 (relatively massive), neutral
What path was most likely to occur in Rutherford's Gold foil experiment?
the alpha particles would go right through the sheet of gold
What path was least likely to occur in Rutherford's Gold foil experiment?
the alpha particles would move directly towards the nucleus, hit the nucleus, and shoot back in the same direction
The nucleus of most atoms is composed of
tightly packed protons and neutrons
t/f: the electron has the same size charge as the proton
true
t/f: the electron is about 2,000 times smaller than the proton
true
What information did Millikan use to determine the charge on an electron?
- the rate at which the oil drop was rising from the plate - the strength of the electric field - the mass of the oil drop
Dalton's atomic theory:
1. All matter is compared of tiny particles called atoms 2. Atoms of a given element are identical in size, mass, and other properties 3. Atoms cannot be subdivided, created, or destroyed 4. Atoms of different elements combine in simple whole number ratios to form chemical compounds 5. In chemical reactions, atoms are combined, separated or rearranged
Differences between Dalton's atomic theory and modern atomic theory:
1. In Dalton's atomic theory, he states that all atoms of a given element are identical in mass, this is not correct. Modern atomic theory states that the masses of atoms of the same substance can be different (aka isotopes) 2. In Dalton's atomic theory, he states that atoms cannot be subdivided. This is also incorrect. Modern atomic theory states that atoms can be divided into protons, neutrons, and electrons.
If 3g of element C combine with 8 g of element D to form compound CD, how many grams of D are needed to form compound CD₂?
16g
Different gases were used inside the tube and different metals were used for electrodes but the results were the same throughout the experiments, what can be concluded from this evidence?
All the particles are the same
Explain how an atom can exist in a neutral state?
Atoms have a positive charged nucleus, made up of protons and neutrons, that is surrounded by a negatively charged electron cloud. The positive and negative charged combine to fork a net neutral change.
Why is Democritus's view of matter considered only an idea, while Dalton's view is considered a theory?
Dalton's view is considered a theory because he has scientific evidence from performing controlled experiments, while Democritus does not.
Who explained the behavior of positively charged particles being deflected from a metal foil as the nucleus?
Ernest Rutherford
A sample of baking soda, NaHCO₃, always contains 27.37% by mass of sodium, 1.20% of hydrogen, 14.30% of carbon, and 57.14% of oxygen. Which law does this data illustrate?
Law of definite proportions
What is the difference between a philosophy and a scientific theory?
Scientific theory has scientific evidence from performing controlled experiments while a philosophy does not.
A molecule of carbon monoxide, CO, has one atom of oxygen while a molecule of carbon dioxide, CO₂, has two. In a sample of CO containing 1 g of C, 1.33g O has combined to form the compound. What law does this illustrate?
The Law of Multiple Proportions
How could you describe J.J. Thomson's model of the atom?
The atom is composed of diffuse ball of positive charge with negative particles dispersed throughout
Every sample of table salt (sodium chloride) contains 39.44% sodium. The remainder is chlorine. What law does this illustrate?
The law of definite proportions
How did Thomson determine that the cathode ray particles were a new particle and not simply an atom, molecule or ion carrying a negative charge?
The m/e was one thousand times smaller than the m/e for any known atom, molecule, or ion.
What determines the charge of an atom?
The number of protons in it's nucleus
A positively charged object attracted the beam and a negatively charged object repelled the beam, what can be concluded from this evidence?
The particles making up the beam are negatively charged
What situation would cause a droplet to be momentarily suspended between the two electrical plates?
The repelling and attracting electrical forces of the plates exactly balances the mass of the droplet.
When a paddle wheel was placed between the cathode and the anode, the ray spun from cathode to anode, what can be concluded from this evidence?
Told us that the beam has mass and volume, therefore it is made up of particles
How does a physical process such as freezing illustrate the law of conservation of mass?
When a liquid freezes, it has the same mass that it had when it was in it's liquid state. The volume may have changed, but the mass always remains the same in physical processes.
Experiments with cathode rays led to the discovery of the
electron
The _________ is the subatomic particle that was discovered first.
electron
In the atom, the electrons are located in the _________.
electron cloud
Location, relative mass, and charge of a electron:
electron cloud, 1/1850 (low mass), negative
The subatomic particles that are least massive and most massive, respectively, are the ________ and _________.
electron, neutron
A cathode ray produced in a gas-filled tube is deflected by a magnetic field. A wire carrying an electric current can be pulled by a magnetic field. A cathode ray is deflected away from a negatively charged object. What property of the cathode ray is shown by these phenomena?
electrons have a negative charge
Isotopes are atoms of the same element that have different
masses
Experiments that showed the cathode ray was attracted to a positive object meant the cathode ray itself was _________.
negative
J.J. Thomson discovered that cathode ray particles carry a negative charge. These negatively charged particles are deflected from their straight-line path when an electric field is applied. What is the charge on the LOWER electrode of the applied electric field?
negative
A nuclear particle that has no electrical charge is called a(n)
neutron
The _________ is a subatomic particle that is electrically neutral.
neutron
Isotopes of an element contain different numbers of
neutrons
Location, relative mass, and charge of a proton:
nucleus, 1 (relatively massive), positive
Rutherford discovered the _________ by performing the _________ experiment.
nucleus, gold foil
Millikan performed the _________ experiment where he measured the _________ of the electron and used it to calculate it's _________.
oil-drop, electric charge, mass
Democritus believed matter was...
particulate (made of particles), (can only be divided into an indivisible particle)
In the gold foil experiment, most of the particles fired at the foil...
passed through the foil
J.J. Thomson discovered that cathode ray particles carry a negative charge. These negatively charged particles are deflected from their straight-line path when an electric field is applied. What is the charge on the UPPER electrode of the applied electric field?
positive
The charge on an alpha particle is positive. Based on this information, the charge of the nucleus must be...
positive
A positively charged particle found in the nucleus is called a(n)
proton
The _________ and _________ are subatomic particles with about the same mass.
proton, neutron
When an object was placed between a cathode and an anode, a sharp shadow was cast, what can be concluded from this evidence?
rays are traveling in a straight line
Alpha particles were chosen for Rutherford's experiment because they are _________ and _________.
small, positively charged
Give an example of a chemical or physical process that illustrates the law of conservation of mass.
In chemical and physical processes, matter is neither created or destroyed. Physical process - 50 g of ice melts into 50g of water Chemical process - iron reacting with oxygen to form rust
How does a chemical process such as rusting illustrate the law of conservation of mass?
In this case, the substance that is produced is just the two elements we already had coming together. The mass doesn't change after the reaction.
Who first proposed an atomic theory based on scientific knowledge?
John Dalton
Is an atom positively charged, negatively charged, or neutral?
Neutral
What is J.J. Thomson's model referred to as?
The "plum pudding" model
How would the electrons produced in a cathode-ray tube filled with neon gas compare with the electrons produced in a cathode-ray tube filled with chlorine gas?
The electrons would behave in the same way because electrons do not differ from element to element.
