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Honors Chemistry-History of the atom (test #3)
Terms in this set (27)
Which ancient Greek thinker was credited with coming up with the idea that matter was composed of particles that were indivisible, thus describing atoms?
Why were Democritus' ideas accepted as opinions rather than facts?
There were no experimental evidence/advanced technology was not present
The foundation of modern chemistry dates back to the century when scientists were able to:
Gather evidence favoring the atomic theory
What were the 3 rules discovered in the late 1700s that helped lay the foundation of modern chemistry?
1. Law of conversation of mass-States that mass is neither created or destroyed during ordinary chemical reactions and physical changes
2. 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; H₂O will always have 11% of hydrogen and 89% Oxygen
3. Law of multiple proportions-If two or more 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; CO is a 1:1, and CO₂ is a 1:2
How did the development of improved balances make the discovery of these 3 laws possible?
People could accurately measure the masses of the elements and compounds
In 1808, John Dalton, an English teacher, proposed an atomic theory that used all three laws; list the 5 statements in Dalton's atomic theory
1.All matter is composed of extremely small particles called atoms
2.Atoms of an element are identical in size, mass, and other properties, and atoms of different elements differ 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
*We know today that number 2 and 3 are false. Number 2 is false because of isotopes and number 3 because atoms can be divisible into smaller particles:subatomic particles and quarks*
The smallest particle of an element that retains the chemical properties of that element
What are the two general areas of an atom
The nucleus and the area surrounding the nucleus (where the electrons are)
Smaller than and occurring in an atom; composes the atom
List the 3 subatomic particles and their electrical charge
Proton - Positive charge
Neutron - Neutral, no charge
Electron - Negative charge
*The protons and neutrons make up the nucleus, while the electrons surround the nucleus*
Positively charged core of an atom (protons and neutrons)
What was the first subatomic particle to be found and by whom?
An electron; John Thomson (J.J)
What was the name of the experiment John Thomson's hypothesis was based on?
Cathode Ray Tube experiment
In 1897, who discovered the charge-to-mass ratio of the cathode-ray particles?
John Thomson (J.J)
In 1909, who is credited with measuring the charge of electrons?
Robert A. Millikan by the Oil Drop experiment
What was John Thomson's plum pudding model of the atom?
The electrons were spread evenly throughout the outside of the nucleus like seeds in a watermelon
*This was quickly disproved but is important because it represents the first time scientists tried to incorporate the then-revolutionary idea that atoms were not indivisible*
In 1911, who worked on the gold-foil experiment?
Ernest Rutherford, Hans Geiger, and Ernest Marsden
What did Rutherford expect to happen when he fired alpha particles, which have a positive charge, at the piece of gold foil?
What actually happened?
Pass right through with slight deflection
1/8,000 alpha particles had been deflected towards the source
What was Rutherford's conclusions?
The force must be caused by a very densely packed bundle of matter with a positive charge, and he called this bundle of matter the nucleus
He discovered the volume of the nucleus was very small to the atom's volume
The nucleus holds which two subatomic particles?
Protons and neutrons
How does the charge of a proton compare to the charge of an electron?
Protons and electrons are equal in magnitude, so they have the same electrical impact. But, electrons are smaller than protons
Why are atoms electrically neutral?
There is an equal quantity of protons and electrons within an atom
Which subatomic particle determines the identity of an element?
Define nuclear force
The short range proton-neutron, proton-proton, and neutron-neutron forces that hold the nuclear particles together;bonded together
In order for there to be a force of attraction between like charged particles, the particle must be
Which two subatomic particles have roughly the same mass?
Protons and neutrons
Most of the mass of an atom is found in the
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