Question

atomic theory part 2- isotopes

check for understanding:
how many neutrons are in chlorine with a mass of 37 amu?

review questions:

1. john dalton’s atomic theory proposed that:

a) atoms are divisible into protons, neutrons, and electrons
b) atoms of a given element are identical in mass and property
c) electrons orbit the nucleus in defined energy levels
d) the nucleus is a dense, positively charged center

1. which experiment led ernest rutherford to conclude that atoms have a small, dense, positively charged nucleus?
2. j.j. thomson is credited with the discovery of which particle, and through which experiment?
3. which of the following best describes isotopes of an element?

a) atoms with the same number of protons but different numbers of neutrons
b) atoms with the same number of neutrons but different numbers of protons
c) atoms with identical mass numbers but different charges
d) atoms that differ only in the number of electrons

1. the atomic mass of an element listed on the periodic table is:

a) the mass of the most common isotope of that element
b) the average mass of all isotopes of the element, weighted by the natural abundance
c) the exact number of protons plus neutrons in the atom
d) the difference between the masses of protons and electrons

Explanation:

Check for understanding:

Step1: Recall atomic structure formula

The formula to find the number of neutrons is \( \text{Number of neutrons} = \text{Mass number} - \text{Atomic number} \). From the periodic table, Chlorine (Cl) has an atomic number of 17 (as seen in the Cl symbol: \( ^{17}\text{Cl} \)). The mass number here is 37 (given as mass of 37 amu).

Step2: Calculate neutrons

Substitute the values into the formula: \( \text{Number of neutrons} = 37 - 17 = 20 \).

John Dalton's Atomic Theory proposed that atoms of a given element are identical in mass and property (option b). Dalton didn't know about subatomic particles (so a is wrong), electrons in energy levels was Bohr's idea (c is wrong), and the nucleus being dense/positive was Rutherford's discovery (d is wrong).

Ernest Rutherford's gold foil experiment (alpha - particle scattering experiment) led him to conclude that atoms have a small, dense, positively charged nucleus. In this experiment, most alpha particles passed through the gold foil, but some were deflected at large angles, indicating a small, dense, positive center (nucleus).

Answer:

20

Review Questions:

1. Question 1