Answer:
A. there is an isotope of lanthanum with an atomic mass of 138.9
Explanation:
By knowing the different atomic masses of both Lanthanum atoms, we can not tell anything about their occurence in nature. Therefore, all the last three options are incorrect. Because, the atomic mass does not tell anything about the availability or natural abundance of an element.
Now, the isotopes of an element are those elements, which have same number of electrons and protons as the original element, but different number of neutrons. Therefore, they have same atomic number but, different atomic weight or atomic masses.
Hence, by looking at an elements having same atomic number, but different atomic masses, we can identify them as isotopes.
Thus, the correct option is:
<u>A. there is an isotope of lanthanum with an atomic mass of 138.9.</u>
The answer is (C) as the definitions states that atomic mass is the number of protons and neutrons.
Hope this helps :).
Answer:
1) -COOH
2) -NH2
3) hydrogen bonds
4) dispersion forces
5) -CH3
6) hydrogen bonds
7) negative
8) negative
9) positive
Explanation:
Alanine has a <u>-COOH</u> and a <u>-NH2</u> group available to form <u>hydrogen bonds</u> with water molecules.
Although there are some potential <u>dispersion forces</u> between the terminal <u>-CH3</u> group of alanine and hexane molecules, we expect the <u>hydrogen bonds</u> between alanine and water to be stronger.
Stronger intermolecular attractive forces between alanine and water lead to a more <u>negative ΔHmix</u> and more <u>negative (smaller positive)</u> ΔHsoln for water than for hexane.
