Chapter 3 Flashcards
Who first defined an atom? How?
Democritus; he defined the atom as the smallest indivisible particle.
chemical reaction
transformation of a substance or substances into one or more new substances
examples of chemical reactions
burning, rusting
law of conservation of mass
matter cannot be created nor destroyed during ordinary chemical reactions or physical changes
law of definite proportions
a chemical compound always contains the same elements in exactly the same proportions by mass regardless of size of the sample or source of the compound
law of multiple proportions
if two or more different compounds are composed of the same two elements, then the ratio of masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers
What are the five postulates of Dalton’s Atomic Theory?
- all matter is composed of extremely small particles called atoms
- atoms cannot be created, destroyed, or subdivided
- atoms of a given element are identical in size, mass, and other properties
- atoms of different elements combine in simple, whole number ratios to form chemical compounds
- in chemical reactions, atoms can be combined, separated, or rearranged
Which two of Dalton’s postulates are incorrect?
- atoms can actually be subdivided into smaller particles known as protons, neutrons, and electrons
- atoms of a given element are not always identical in mass due to varying number of neutrons in isotopes
atom
smallest particle of an element that retains its chemical properties
nucleus
very small region located at the center of the atom
What is the nucleus made up of?
subatomic particles known as protons and neutrons
What is the nucleus’ charge?
positive
What surrounds the nucleus?
electron cloud made up of negatively charged particles called electrons
Electrical charge, mass number, and location of subatomic particles?
- proton- electrical charge is positive, mass number is one, and location is inside the nucleus
- neutron- no charge, mass number is one, and location is inside nucleus
- electron- negative charge, mass number is zero, and location is outside of nucleus in electron cloud
Who are the three main people that used experiments to discover important parts about the atom?
Rutherford, Robert A. Millikan, and JJ Thompson
What was JJ Thompson’s experiment, and what did he discover?
JJ Thompson used a cathode ray tube to measure the charge to mass ratio of an electron; he deflected the negatively charged particles of the cathode ray with a magnet because opposite charges attract
What was Robert A. Millikan’s experiment, and what did he discover?
Millikan used the oil drop experiment to measure the charge of an electron. He set up a tube where electrons would latch onto oil droplets and fall through a hole into an electrically charged area where negatively charged particles would float against gravity.
How were scientists able to find the mass of an electron?
Using the information found from Thompson’s and Millikan’s experiments, the mass and charge of an electron could be determined.
What was Rutherford’s experiment, and what did he discover?
Rutherford did the gold foil experiment and discovered the nucleus. He shot positive particles through an atom, and these particles deflected off of the nucleus because similar particles repel.
How was Rutherford able to determine the size of the nucleus?
Since positive particles reflected off of the nucleus, he could look at the area where particles were not deflected and infer the size of the nucleus.
What is an atom’s charge?
electrically neutral because the positive charge is equal to the negative charge
How do nuclei of different elements differ?
they only differ in their number of protons and the amount of positive charge they possess
What determines an atom’s identity?
number of protons
What is a strong nuclear force?
an attraction between two subatomic/ nuclear particles, such as proton-neutron, proton-proton, neutron-neutron, etc.
size of atoms
radius of an atom is the distance from the center of the nucleus to the outer portion of the electron cloud
What is the unit of measurement for an atom?
picometer
What is the atomic number?
the number of protons in each atom of an element
How many protons do different atoms of the same element have?
all atoms of the same element contain the same amount of protons
What are isotopes?
atoms of the same element that have different masses
Compare and contrast isotopes.
all isotopes have the same number of protons and electrons and a different number of neutrons
What to most elements consist of?
mixtures of isotopes
What is the mass number?
total number of protons and neutrons in the nucleus
What is hyphen notation?
the name of the element, a hyphen, and then the mass number
example of hyphen notation
Carbon-12
What is a nuclide?
general term for a specific isotope of an element
What is standard relative mass?
comparing units of atomic mass, or amu, to the atomic mass of a Carbon-12 atom
What is the standard relative mass of Carbon-12?
12 amu
What is one atomic mass unit equal to?
one amu is equal to 1/12 the mass of a Carbon-12 atom
What is the average atomic mass?
the weighted average of atomic masses of naturally occurring isotopes of an element
How is average atomic mass found?
multiplying the atomic mass of each isotope with its relative abundance in decimal form and adding the results
What is a mole?
amount of substance that contains as many particles as there are atoms in exactly 12g of Carbon-12
What is Avagadro’s number?
6.022 x 10^23
What does Avagadro’s number represent?
number of particles in exactly one mole of a pure substance
What is molar mass?
mass of one mole of a pure substance
What is the unit for molar mass?
g/mol
What is molar mass equal to?
numerically equal to atomic mass of an element in amu
