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Flashcards in Ch 3 Section 2 Deck (58):
1

Atom

Smallest particle of an element that retains the chemical properties of that element

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All atoms consist of

2 regions

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Nucleus

Very small region at the center of an atom

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Nucleus is made up of at least one

Positively charged particle called a proton and usually one or more neutral particles called neutrons

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Surrounding the nucleus is a region occupied by

Negatively charged particles called electrons

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Electrons region is very

Large compared with nucleus

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Subatomic particles

Proton
Neutron
Election

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First discovery of a subatomic particle resulted from investigations into

Relationship between electricity and matter

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Many experiments performed in which electric current was passed

Through various gases at low pressures

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As scientific advances allowed a deeper exploration of matter it became clear that atoms are actually composed of several basic types of

Smaller particles and that the number and arrangement of these particles determine that atoms chemical properties

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Those experiments carried out in

Cathode ray tubes

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When current was passed through a cathode ray tube surface of tube

Directly opposite the cathode glowed

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Hypothesized that glow was caused by a

Stream of particles, a cathode ray

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Ray traveled from cathode to

Anode when current was passed through the tube

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Cathode Rays were deflected by a

Magnetic field in the same manner as a wire carrying electric current which is know to have negative charge

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Rays were deflected

Away from a negatively charged object

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Observations led to hypothesis that particles that commode cathode Rays are

Negatively charged

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Cathode ray hypothesis supported by

JJ thomsons experiments

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Thomson was able to measure the ratio of the charge of

Cathode Ray particles to their mass and found that ratio was always the same

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Thomson concluded that all cathode Rays are composed of

Identical negatively charged particles called electrons

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Cathode Rays have identical properties regardless of the

Element used to produce them

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Concluded that electrons are present in

Atoms of all elements

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Cathode ray experiments provided evidence that atoms are

Divisible and that one of an atoms basic constituents is the electron

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Thomsons experiment revealed that the electron has a very large

Charge to mass ratio

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Robert a Millikan measured

The charge of the electron

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Scientists used the charge of the electron and the charge to mass ratio of the electron to determine that an electrons mass is about

1/2000 the mass of the simplest type of hydrogen atom

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Simplest type of hydrogen atom

Smallest atom known

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Electron actually has a mass of

1/1837 the mass of the simplest hydrogen atom

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Because atoms are electrically neutral they must contain a

Positive charge to balance the negative electrons

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Because electrons have so much less mass than atoms atoms must contain

Other particles that account for most of their mass

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Thomson proposed the plum pudding model-> negative electrons were spread evenly throughout the

Positive charge of the rest of the atom

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Ernest Rutherford, Hans greiger, and Ernest mars den bombarded a thin piece of

Gold foil with fast moving alpha particles

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Alpha particles are positively charged particles with about

4x the mass of a hydrogen atom

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Greiger and marsden assumed that mass and charge were

Uniformly districts throughout atoms of gold foil

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Expected alpha particles to pass through with only a slight

Deflection and for vast majority of particles that was the case

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When they checked for the possibility of wide angle deflections they found that approx

1 in 8000 alpha particles were deflected back toward the source

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Rutherford reasoned that deflected alpha particles must have experienced some

Powerful force within the atom

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Rutherford concluded that the force must be caused by a very densely packed

Bundle of matter with a positive electric charge, the nucleus

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Rutherford discovered that volume of nucleus was very

Small compared with total volume of an atom

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Niels Bohr proposed a model in which electrons

Surrounded the positively charged nucleus

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Except for the nucleus of the simplest type of hydrogen atom all atomic nuclei are made of

Protons and neutrons

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A proton has a positive charge equal in

Magnitude to the negative charge of an electron

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Atoms are electrically neutral because they contain

Equal numbers of protons and electrons

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Neutrons are

Electrically neutral

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Simplest hydrogen atom consists of a single

Proton nucleus with a single electron moving about it

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A proton has a mass 1836 times greater than

That of an electron

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The nuclei of atoms of different elements differ in their number of

Protons and thus in the amount of positive charge they possess

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Number of protons determines

Atoms identity

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Particles other than electrons protons and neutrons have little

Effect on the chemical properties of matter

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Generally particles that have the same electric charge

Repel one another

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When 2 protons are extremely close to each other there is a strong

Attraction between them

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As many as ---- protons can exist

83 protons can exist close together to help form a stable nucleus

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Nuclear forces: short Range

Proton-neutron, proton-proton, and neutron-neutron forces that hold nuclear particles together

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Electron cloud: region occupied by

Electrons, cloud of negative charge

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Radius of an atom is the distance from

Center of the nucleus to the outer portion of the electron cloud

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Because atomic radii are so small they are expressed using

The pico meter (pm)

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Atomic radio range from about

49 to 270 pm

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Nuclei of atoms have radiu about

.001 pm and incredibly high densities (2 x 10^8 metric tons per cm^3)