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3 years ago

The existence of isotopes violates one of the original ideas of Dalton's atomic theory. Which one?

Chemistry

1 answer:

Colt1911 [192]3 years ago

3 0

Explanation:

One of the Dalton's postulates states that:

The atoms of same element are similar in the shape and the mass and other properties but different from atoms of other elements.

But the existence of isotopes violates this postulate because isotopes are the species which have same atomic number but different atomic mass. For example, carbon exist in three isotopes which are C-12, C-13 and C-14 and have different mass and some properties and is a contradiction of this postulate.

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All chemicals should be stored in ?

netineya [11]

im a container or a glass

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3 years ago

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A heating curve has two flat lines, or plateaus. What does the plateau at the lower temperature represent?

masya89 [10]

Answer:

B) Melting of a solid.

Explanation:

Kindly, see the attached image.

It is known that the substance has different 3 phases (solid, liquid, and gas).

By heating, the substance converted from solid phase to liquid phase passing by a plateau that represents equilibrium between the two phases.

By further heating, the solid completely converted into liquid phase, then converted to gaseous phase passing by a plateau that represents an equilibrium between the liquid an gaseous phase.

The plateau at the lower temperature represent: B) Melting of a solid.

8 0

3 years ago

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Uranium-235 decays to form lead-207. The half-life of uranium-235 is 704,000,000 years. What is the approximate age of an igneou

Strike441 [17]

Answer:

The approximate age of the igneous rock is $7.042\times 10^{6}$ years.

Explanation:

Chemically speaking, the Uranium-235 decays to form Lead-207 throughout time. All isotopes decay exponentially by means of the following model:

$m(t) = m_{o}\cdot e^{-\frac{t}{\tau} }$ (1)

In addition, we can determine the time constant of the former isotope in terms of its half life, that is:

$\tau = \frac{t_{1/2}}{\ln 2}$ (2)

Where:

$m_{o}$ - Initial mass of Uranium-235, in atoms.

$m(t)$ - Current mass of Uranium-235, in atoms.

$\tau$ - TIme constant, in years.

$t_{1/2}$ - Half-life of Uranium-235, in years.

Please remind that a 1 : 1 ratio of Uranium-235 to Lead-207 atoms means that current mass of Uranium-235 is a half of its initial mass. If we know that $m(t) = 0.5\cdot m_{o}$ and $t_{1/2} = 7.04\times 10^{8}\,yr$ , then the approximate age of the igneous rock is:

$\tau = \frac{7.04\times 10^{8}\,yr}{\ln 2}$

$\tau \approx 1.016\times 10^{9}\,yr$

$t = -\tau \cdot \ln \left(\frac{m(t)}{m_{o}} \right)$

$t = -(1.016\times 10^{9}\,yr)\cdot \ln \frac{1}{2}$

$t \approx 7.042\times 10^{6}\,yr$

The approximate age of the igneous rock is $7.042\times 10^{6}$ years.

5 0

3 years ago

Determine the identity of the daughter nuclide from the electron capture by 3517cl. determine the identity of the daughter nucli

brilliants [131]

Answer:

$^{35}_{16}S$

Explanation:

When the nucleus of an atom captures and electron, such electron combines with a proton and forms a neutron. Thus, the mass number remains the same (just a proton has been converted into a neutron) but the atomic number (the number of protons) decrease in one.

Then, the daughter nuclide will have the same mass number and the atomic number reduced in one.

The given parent isotope is $^{35}_{17}Cl$ , which means that it has these features:

Chemical symbol: Cl

Name of the element: chlorine

Mass number (the superscript to the left): 35

Atomic number (the subscript to the left): 17

And the daughter nuclide after the electron capture will be:

Mass number: 35 (the same of the parent nuclide)

Atomic number: 17 - 1 = 16

Identity: sulfur (search the element with atomic number 16 in a periodic table).

Chemical symbol: S

Idenity of the daughter nuclide using the isotope notation:

$^{35}_{16}S$

Hence, the answer is the third choice.

4 0

3 years ago

If you were asked to convert 25 mg to the unit hg, which of the following would be the first fraction used in the conversion? te

NemiM [27]

The conversion factor is added to the original given unit so that you can end up with the final unit. Basically, the conversion unit does not change the value because the factor is just equal to 1. You just manipulate the units by cancelling them.

Among the given choices, the fraction which is equal to 1 is 10⁻³ g/ 1 mg, because there are 1,000 mg per 1 g. In reverse, that would be 10⁻³ of a gram.

6 0

3 years ago