question 1
*according to daltons atomic theory, atoms were indivisible; they could not be broken down into smaller pieces. in 1904, j.j. thomson proposed that he had found a sub - atomic particle.*

a) what was the name of the piece of equipment used by thomson?
b) what did thomson call the particle that he had discovered, and what was the charge on this particle?
c) overall, matter is neutral (does not have a charge). what other sub - atomic particle did thomson suggest must also be present in an atom?
d) what model of the atom did thomson propose? how are the sub - atomic particles arranged?

question 2
naturally occurring magnesium (mg) consists of a mixture of three isotopes, as follows:
78.9% of mg - 24, atomic mass of 23.98 amu
10.0% mg - 25, atomic mass of 24.98 amu and 11.1% of mg - 26, atomic mass of 25.98 amu. calculate the average atomic mass of magnesium?

Question

question 1
*according to daltons atomic theory, atoms were indivisible; they could not be broken down into smaller pieces. in 1904, j.j. thomson proposed that he had found a sub - atomic particle.*

a) what was the name of the piece of equipment used by thomson?
b) what did thomson call the particle that he had discovered, and what was the charge on this particle?
c) overall, matter is neutral (does not have a charge). what other sub - atomic particle did thomson suggest must also be present in an atom?
d) what model of the atom did thomson propose? how are the sub - atomic particles arranged?

question 2
naturally occurring magnesium (mg) consists of a mixture of three isotopes, as follows:
78.9% of mg - 24, atomic mass of 23.98 amu
10.0% mg - 25, atomic mass of 24.98 amu and 11.1% of mg - 26, atomic mass of 25.98 amu. calculate the average atomic mass of magnesium?

Accepted Answer

### Question 1 (Subfield: Chemistry)
#### Part a
# Brief Explanations:
J.J. Thomson used a cathode ray tube to discover the sub - atomic particle. The cathode ray tube is a device that emits cathode rays (streams of electrons) when a high voltage is applied across two electrodes in a partially evacuated tube.
# Answer:
a) Cathode ray tube

#### Part b
# Brief Explanations:
Thomson called the particle he discovered an electron. Electrons are negatively charged sub - atomic particles. The charge of an electron is approximately $- 1.6\times10^{-19}$ coulombs, and in terms of the elementary charge, we say it has a charge of $-1$ (relative to the proton's $ + 1$ charge).
# Answer:
b) The particle was called an electron, and its charge is negative (or $-1$ elementary charge or $-1.6\times10^{-19}$ C)

#### Part c
# Brief Explanations:
Since matter is neutral and electrons have a negative charge, Thomson suggested that there must be positively charged sub - atomic particles present in the atom to balance the negative charge of electrons. These positively charged particles were later understood to be protons (though Thomson's initial model had a more diffuse positive charge).
# Answer:
c) Positively charged particle (proton - like, in the context of balancing charge)

#### Part d
# Brief Explanations:
Thomson proposed the plum - pudding model of the atom. In this model, the atom is thought of as a sphere of positive charge (like the pudding) with electrons (like plums) embedded within it, distributed throughout the positive charge to make the atom electrically neutral.
# Answer:
d) Plum - pudding model; Electrons are embedded in a sphere of positive charge

### Question 2 (Subfield: Chemistry)
# Explanation:
## Step 1: Recall the formula for average atomic mass
The formula for calculating the average atomic mass ($A$) of an element with isotopes is $A=\sum_{i = 1}^{n}(f_{i}\times m_{i})$, where $f_{i}$ is the fractional abundance of isotope $i$ and $m_{i}$ is the atomic mass of isotope $i$. First, we need to convert the percentage abundances to fractional abundances by dividing each percentage by 100.

## Step 2: Calculate the fractional abundances
- For Mg - 24: $f_{1}=\frac{78.9}{100}=0.789$, $m_{1} = 23.98$ amu
- For Mg - 25: $f_{2}=\frac{10.0}{100}=0.100$, $m_{2}=24.98$ amu
- For Mg - 26: $f_{3}=\frac{11.1}{100}=0.111$, $m_{3}=25.98$ amu

## Step 3: Calculate the contribution of each isotope to the average atomic mass
- Contribution of Mg - 24: $0.789\times23.98=0.789\times23.98\approx18.92$ amu
- Contribution of Mg - 25: $0.100\times24.98 = 2.498$ amu
- Contribution of Mg - 26: $0.111\times25.98=0.111\times25.98\approx2.884$ amu

## Step 4: Sum the contributions
$A=18.92 + 2.498+2.884=24.302\approx24.30$ amu

# Answer:
The average atomic mass of magnesium is approximately $24.30$ amu

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Explanation:

Question 1 (Subfield: Chemistry)

Part a

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Part b