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PreAP Chemistry Chapter 3. Democritus was the early Greek philosopher who is credited with the concept of the atom (atomos) –which means invisible. Democritus was the early Greek philosopher who is credited with the concept of the atom (atomos) –which means invisible

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Democritus was the early Greek philosopher who is credited with the concept of the atom (atomos) –which means invisible


Democritus was the early Greek philosopher who is credited with the concept of the atom (atomos) –which means invisible

Law of Definite Proportions states that the elements in a specific compounds always contain the same proportions by mass.


Law of Multiple Proportions states that 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


Dalton is an English school teacher who proposed the law of conservation of mass, the law of definite proportions, and the law of multiple proportions.


Dalton is an English school teacher who proposed the law of conservation of mass, the law of definite proportions, and the law of multiple proportions.

He is also known as the Father of the Atomic Theory


Dalton’s atomic theory

1.All matter is composed of very small particles called atoms


  • Dalton’s atomic theory

  • All matter is composed of very small particles called atoms

  • Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in these properties.


3.Atoms cannot be subdivided, created, or destroyed


  • Atoms cannot be subdivided, created, or destroyed

  • 4.Atoms of different elements combine in simple whole-number ratios to form chemical compounds.


  • 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.




Atom incorrect: --smallest particle of an element that retains the properties of that element.


Two regions of an atom incorrect:

1. Nucleus -- small region near the center of the atom.

Composed of two particles—the proton which is positively charged and the neutron which is neutral (zero) charged.


2. incorrect:Electron Cloud --composed of negatively charged electrons. It is very large in comparison to the nucleus.


2. incorrect:Electron Cloud --composed of negatively charged electrons. It is very large in comparison to the nucleus.

Subatomic particles—protons, neutrons, electrons


2. incorrect:Electron Cloud --composed of negatively charged electrons. It is very large in comparison to the nucleus.

Subatomic particles—protons, neutrons, electrons

Cathode Ray tubes — the instrument used in the discovery of the electron


J. J. Thomson incorrect: is the man credited with the discovery of the electrons in the late 1800’s


J. J. Thomson incorrect: is the man credited with the discovery of the electrons in the late 1800’s

Millikan discovered the mass of the electrons


Knowledge of electrons led to two inferences about atomic structure:

1.Because atoms are electrically neutral, they must contain positive charge to balance the negative electrons.


Knowledge of electrons led to two inferences about atomic structure:

1.Because atoms are electrically neutral, they must contain positive charge to balance the negative electrons.

2.Because electrons have so little mass, atoms must contain other particles to account for most of their mass


Nucleus of the atom—discovered by structure:Lord Ernest Rutherford


Nucleus of the atom—discovered by structure:Lord Ernest Rutherford

Gold foil experiment—actually done by Hans Geiger and Ernest Marsden


  • Observations: structure:

  • Majority of the alpha (α)particles penetrated foil undeflected.

  • b.About 1 in 20,000 were slightly deflected

  • c.About 1 in 20,000 were deflected back to emitter


Conclusions: 1. Mass of the atom and the positive charge are concentrated in small regions called nucleus


Conclusions: 1. Mass of the atom and the positive charge are concentrated in small regions called nucleus

2. Most of the atom is empty


  • Conclusions: 1. Mass of the atom and the positive charge are concentrated in small regions called nucleus

  • Most of the atom is empty

  • 3.Magnitude of charge on the nucleus is different for different atoms


4. Number of 1. electrons outside the nucleus = number of units of nuclear charge (to account for the fact that the atom is electrically neutral)


4. Number of 1. electrons outside the nucleus = number of units of nuclear charge (to account for the fact that the atom is electrically neutral)

Atoms are electrically neutral because they contain equal numbers of protons and electrons


1. What kinds of particles are being emitted by the radioactive source? What is their charge?

















Nuclear Forces atom had been thinly spread out throughout the atom? the short-range proton-neutron, proton-proton, and neutron-neutron forces that hold the nuclear particles together


Nuclear Forces atom had been thinly spread out throughout the atom? the short-range proton-neutron, proton-proton, and neutron-neutron forces that hold the nuclear particles together

Mass of one proton = mass of neutron = mass of 1837 electrons


Atomic number—the number of atom had been thinly spread out throughout the atom?protons in the nucleus of the atom.


Atomic number—the number of atom had been thinly spread out throughout the atom?protons in the nucleus of the atom.

--number of protonsidentifies the

element and is equal to the number of electrons (of a neutral atom)

--symbol is Z


Isotopes atom had been thinly spread out throughout the atom? are atoms of the same element that have different masses because they have different numbers of neutrons but they still have similar chemical properties


Isotopes atom had been thinly spread out throughout the atom? are atoms of the same element that have different masses because they have different numbers of neutrons but they still have similar chemical properties

Mass number – approximate atomic mass of an atom (nucleus)

-- the number of protons + neutrons


Isotopes of Carbon atom had been thinly spread out throughout the atom?


Isotopes of Carbon atom had been thinly spread out throughout the atom?


Nuclide atom had been thinly spread out throughout the atom? is the general term for any isotope of any element


Nuclide atom had been thinly spread out throughout the atom? is the general term for any isotope of any element

Atomic Mass Unit (amu) is exactly 1/12 the mass of a carbon-12 atom


Average atomic mass atom had been thinly spread out throughout the atom? is the weight average of the atomic masses of the naturally occurring isotopes of an element.

Ave. Atomic mass = %abundace(mass of isotope 1) + %abundance(mass of isotope 2) +…..


Moles atom had been thinly spread out throughout the atom?

Mole (mol) is the amount of a substances that contains as many particles as there are atoms in exactly 12 g of carbon-12

(Mole comes from the German word for “pile”)


Avogadro’s atom had been thinly spread out throughout the atom? number – 6.022 ×1023 – is the number of particles in exactly 1 mole of a pure substance. Just as one dozen = 12 somethings, one mole = 6.022 ×1023 somethings.


The mass of one mole of a pure substance (element or compound) is called the molar mass of that substance. The unit is


Mole Review compound) is called the


How many grams are in 2.0 mol Carbon? compound) is called the


How many grams are in 2.0 mol Carbon? compound) is called the


How many grams are in 2.0 mol Carbon? compound) is called the


How many grams are in 2.0 mol Carbon? compound) is called the


How many grams are in 2.0 mol Carbon? compound) is called the


How many moles are in 0.58 g Al? compound) is called the


How many moles are in 0.58 g Al? compound) is called the


How many moles are in 0.58 g Al? compound) is called the


How many moles are in 0.58 g Al? compound) is called the


How many moles are equal to 1.20 x 10 compound) is called the 25 atoms of sodium? (Na)


How many moles are equal to 1.20 x 10 compound) is called the 25 atoms of sodium? (Na)




What is the mass in grams of 4.75 x 10 compound) is called the 24 atoms of silver? (Ag)


What is the mass in grams of 4.75 x 10 compound) is called the 24 atoms of silver? (Ag)




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