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Honors Chemistry: History of the Atom
Terms in this set (69)
Greek philosopher that said all matter is made of tiny particles called atoms
Why did everyone not believe Democritis when he suggested the existence of Atoms?
Aristotle did not believe in atoms and rather believed in continuous matter (uninterrupted blobs of matter)
Everyone believed Aristotle
Dalton's Atomic Theory
1. Each element is composed of small particles called atoms
2. Atoms are invisible and indestructible
3. Atoms of an element are identical
4. Atoms of one element are different from atoms or other elements (true to this day)
5. Compounds always have the same ratios of the same atoms (law of definite proportions)
6. In chemical reaction, atoms are separated, combined or rearranged (law of conversation of matter)
law of definite proportions
Compounds always have the same ratios of the same atoms
a statement in chemistry: every definite compound always contains the same elements in the same proportions by weight.
law of conversation of matter
In chemical reaction, atoms are separated, combined or rearranged but mass stays the same
matter is neither created nor destroyed, so we must have the same number and type of atoms after the chemical change as were present before the chemical change.
J.J. Tomson (1897)
Disovered that atoms had electrons
-Cathode Ray Tube
Who proposed the Plum pudding model?
What was the plum pudding model?
an early model of what the structure of atoms was thought to be like
What was the cathode ray tube?
vacuum tube containing electron gun
Ernest Rutherford (1871-1937)
in 1911, he performed his famous gold-foil experiment and discovered the nucleus of the atom.
What was the gold foil experiment?
Rutherford shot alpha particles (double positive charge) at a thin sheet of gold, and the particles that bounced back led him to discover the dense mass at the center of the atom called the nucleus
Discovered the neutron in 1932
Determined the charge of an electron
Oil drop experiment
the oil drop experiment?
A drop of oil was placed in a cylinder with negative and positive plates, the drops were charged using an x-ray. Different waves of xrays let the drops fall at different rates. Determined that the mass of the electron is 9.10 x 10^-28 by Robert Milikan
atomic number on periodic table
Atomic number definition
number of protons in the nucleus
What happens in the Elements is neutral? (0 overall charge)
Protons = electrons
mass number on periodic table
Mass number (A)
the sum of the number of neutrons and protons in an atomic nucleus
Number of nuetrons =
Mass Number (a) - Atomic Number (z) (mass number minus protons)
Atoms of the same element that have different numbers of neutrons
Isotopes always have the same...
Isotopes always have a different...
Atomic Mass (AMU)
The average mass of all the isotopes of an element (decimal number on periodic table)
-Percent abundance of Isotopes
Modern Periodic Law
When elements are arranged in order of increasing atomic number, there is a repetition of their chemical and physical properties
constructed a useful way into organizing the periodic table by rows and columns
Vertical columns are called?
groups or families
Horizontal rows are called?
Rows or periods
How many families?
How many rows?
Alkali metals =
alkaline earth metals =
Noble gases =
Where are metals located on the periodic table?
Characteristics of metals:
1. Solids at room temp.
2. Malleable (can be pounded into different shapes)
3. Ductile (can be drawn into a wire) Flexible
4. Conductors of heat and electricity
5. high melting and boiling points
6. Lose an electron to become positive cations
Where are nonmetals located on the periodic table?
Characteristics of Nonmetals:
1. Generally gas or liquid
2. If not liquid or gas, brittle solid
3. nonconductors (dont make heat and electricity)
4. Gain or share electrons
Elements along the stair step line dividing the periodic table
Both metals and nonmetals
shows characteristics of both
Elements where 2 atoms of the same element are bonded together
Dont have to be paired up in a compound Either bonded to another element or to themselves HOBrFINCL
What are the Diatomic elements?
H2, N2, O2, F2, Cl2, Br2, I2
positive charge, lose electrons
negative charge, gain electrons
Outermost electrons in an atom
are involved in the bonds that atoms form
Group 1 =
1 valance electron
Group 2 =
2 valence electrons
Group 3 =
3 valence electrons
protons have a ___ charge
Electrons have a ____ charge
Where are protons and neutrons are located?
Where does most of the nucleus mass come from?
Neutrons and protons
The atom is consisted of mostly what?
What does a neutral atom have?
a equal amount of protons and electrons
The subatomic particle with the least amount of mass is?
A cathode ray tube consists of?
The electron was discovered by
The scientist who measured the charge of the electron was
Rutherford called the core of the atom the
What particle is normally found on the outside of the nucleus of the atom?
An elements identity is determined by its?
An ion always contains an unequal number of ...?
Protons and electrons
Two atoms are isotopes if they contain...
The same number of protons but different numbers of neutrons
The force that holds protons together are
Strong nuclear force
Who classified elements into triads?
The scientist who observed a pattern of properties that repeated every eight elements was
Who discovered the concept of atomic number?
How many labeled groups are in the periodic table?
Electrons that are largely responsible for an atoms chemical behavior are called?
When an atom loses an electron, it becomes
smaller in radius and positive in charge
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