Q: Calculate the average atomic mass of an element with two isotopes: 70% of isotope X-35 (mass = 35 amu) and 30% of isotope X-37 (mass = 37 amu).

$$(0.70 \times 35) + (0.30 \times 37) = 35.6$$ amu

Q: Which of the following is the correct formula for calculating average atomic mass?

$$\text{average atomic mass} = (\text{abundance}_1 \times \text{mass}_1) + (\text{abundance}_2 \times \text{mass}_2) + \ldots$$

Question 1

Which experiment led to the discovery of the nucleus in the atom, and what was the key observation that supported this discovery?

Accepted Answer

Rutherford's gold foil experiment; the observation that a small fraction of alpha particles were deflected at large angles.

Question 2

Which of the following statements about isotopes is correct?

Accepted Answer

Isotopes of an element have the same number of protons and electrons, but different numbers of neutrons.

Question 3

A neutral atom of beryllium (Be) has an atomic number $$Z = 4$$ and a mass number $$A = 9. $$How many protons, neutrons, and electrons does it have?

Accepted Answer

4 protons, 5 neutrons, 4 electrons

Question 4

Which group on the periodic table is known for being highly unreactive, and why?

Accepted Answer

Group 18 (Noble Gases); because they have a complete set of valence electrons.

Question 5

If a chlorine atom (atomic number 17) gains one electron, what type of ion is formed and what is its charge?

Accepted Answer

An anion with a $$-1$$ charge

Question 6

Which of the following best describes the difference between atomic mass and mass number?

Accepted Answer

Atomic mass is the weighted average of all isotopes of an element; mass number is the total number of protons and neutrons in a specific atom.

Question 7

Which subatomic particle is responsible for the chemical properties and reactivity of an element?

Accepted Answer

Electron

Question 8

Calculate the average atomic mass of an element with two isotopes: 70% of isotope X-35 (mass = 35 amu) and 30% of isotope X-37 (mass = 37 amu).

Accepted Answer

$$(0.70 	imes 35) + (0.30 	imes 37) = 35.6$$ amu

Question 9

Which of the following statements about the periodic table is correct?

Accepted Answer

Elements in the same group have similar chemical properties due to similar valence electron configurations.

Question 10

A neutral atom has 15 protons, 16 neutrons, and 15 electrons. Write its nuclide symbol.

Accepted Answer

$$^{31}_{15}\mathrm{P}$$

Question 11

Which of the following best explains why the symbol 'Co' represents cobalt and not carbon monoxide?

Accepted Answer

Element symbols are case-sensitive; 'Co' is cobalt, while 'CO' is carbon monoxide.

Question 12

Which particle(s) are found in the nucleus of an atom?

Accepted Answer

Protons and neutrons

Question 13

If an atom loses two electrons, what is the resulting charge and what is the ion called?

Accepted Answer

Charge $$= +2$$, called a cation

Question 14

Which of the following is the correct formula for calculating average atomic mass?

Accepted Answer

$$	ext{average atomic mass} = (	ext{abundance}_1 	imes 	ext{mass}_1) + (	ext{abundance}_2 	imes 	ext{mass}_2) + \ldots$$

Question 15

Which of the following best describes why elements in Group 1 (alkali metals) are highly reactive?

Accepted Answer

They have one valence electron, which they readily lose to achieve a stable noble gas configuration.

Question 16

Which of the following is NOT a correct statement about the modern atomic theory?

Accepted Answer

Atoms are indivisible and cannot be broken down further.

Question 17

A sample of chlorine contains 75.77% chlorine-35 (mass = 34.969 amu) and 24.23% chlorine-37 (mass = 36.966 amu). Calculate the average atomic mass of chlorine.

Accepted Answer

$$(0.7577 	imes 34.969) + (0.2423 	imes 36.966) = 35.45$$ amu

Question 18

Which of the following best explains why the periodic table is arranged by atomic number rather than atomic mass?

Accepted Answer

Atomic number reflects the number of protons, which determines the element's identity and chemical properties.

Question 19

Which of the following is a correct nuclide symbol for Uranium-238?

Accepted Answer

$$^{238}_{92}\mathrm{U}$$

Question 20

Which of the following best describes the charge and relative mass of an electron compared to a proton?

Accepted Answer

Electrons have a charge of $$-1$$ and a much smaller mass than protons.

Atoms and Elements: Foundations of Atomic Theory and the Periodic Table

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