Which best describes the geologic time scale? It explains why events happen throughout Earth’s history. It presents the correct sequence of events in Earth’s history. It is used to determine the absolute dates in years for different periods.

3 0

3 years ago

The element boron exists in nature as two isotopes: 10B has a mass of 10.0129 u, and 11B has a mass of 11.0093 u. The average at

Shalnov [3]

Answer:

Percentage abundance of B 10 is = 20 %

Percentage abundance of B 11 is = 80 %

Explanation:

The formula for the calculation of the average atomic mass is:

$Average\ atomic\ mass=(\frac {\%\ of\ the\ first\ isotope}{100}\times {Mass\ of\ the\ first\ isotope})+(\frac {\%\ of\ the\ second\ isotope}{100}\times {Mass\ of\ the\ second\ isotope})$

Given that:

Since the element has only 2 isotopes, so the let the percentage of first be x and the second is 100 -x.

For first isotope, B 10:

% = x %

Mass = 10.0129 u

For second isotope, B 11:

% = 100 - x

Mass = 11.0093 u

Given, Average Mass = 10.81 u

Thus,

$10.81=\frac{x}{100}\times {10.0129}+\frac{100-x}{100}\times {11.0093}$

$10.0129x+11.0093\left(100-x\right)=1081$

Solving for x, we get that:

x = 20 %

Thus percentage abundance of B 10 is = 20 %

Percentage abundance of B 11 is = 100 - 20 % = 80 %

8 0

3 years ago

Read 2 more answers

Is Ca-Ci a covalent or ionic bond and why?

taurus [48]

Ionic bond

Explanation:

Ca - Cl₂ is an ionic bond because it involves a true metal and a non-metal.

An ionic bond is an inter-atomic bond between two chemical species.

This bond forms between two atom with a large electronegative difference.
Often times, this corresponds to a metal and a non-metal.
The metal is the less electronegative specie and the non-metal is more electronegative
The metal such as Ca loses two electrons to become positively charge ion.
The non-metal gains the electrons. Here two atoms of Cl are turned to ions.
Electrostatic attraction between the metal and non-metal forms the ionic bonding.

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Ionic bond brainly.com/question/6071838

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5 0

3 years ago