Q: Which of the following pairs of ions have the same number of electrons?

$$\mathrm{Cl^-}$$ \text{ and } \mathrm{Br^-}$

Q: Calculate the atomic mass of a hypothetical element Hy with three isotopes: Hy-299 (5.00%, 299.0 amu), Hy-300 (65.00%, 300.0 amu), and Hy-301 (30.00%, 301.0 amu).

$$0.05 \times 299.0 + 0.65 \times 300.0 + 0.30 \times 301.0 = 299.75 + 195.0 + 90.3 = 300.3\ \mathrm{amu}$$

Question 1

Which of the following statements best illustrates the relative size of atoms compared to everyday objects, as described in the study materials?

Accepted Answer

If every atom in a pebble were the size of the pebble itself, the pebble would be larger than Mount Everest.

Question 2

Which part of Dalton’s Atomic Theory was later found to be incorrect based on modern discoveries?

Accepted Answer

Atoms of a given element are identical in mass and properties.

Question 3

Which experiment provided direct evidence for the existence of atoms by manipulating individual xenon atoms to spell out 'IBM'?

Accepted Answer

Scanning tunneling microscope (STM) experiment

Question 4

Which model of the atom is depicted by a sphere of positive charge with electrons embedded throughout, as proposed by J.J. Thomson?

Accepted Answer

Plum pudding model

Question 5

According to Rutherford’s nuclear theory, where is most of the mass and all of the positive charge of an atom located?

Accepted Answer

In the nucleus

Question 6

Which subatomic particle has the least mass?

Accepted Answer

Electron

Question 7

What is the atomic number (Z) of an element defined as?

Accepted Answer

The number of protons in the nucleus

Question 8

Which element has the chemical symbol 'Pb'?

Accepted Answer

Lead

Question 9

Which of the following elements is a metalloid and is widely used in the electronics industry due to its semiconducting properties?

Accepted Answer

Silicon

Question 10

Which group in the periodic table contains elements that are highly reactive with water and include sodium and potassium?

Accepted Answer

Alkali metals

Question 11

A neutral atom of chlorine has 17 protons and 18 neutrons. What is its mass number?

Accepted Answer

$$17 + 18 = 35$$

Question 12

Which of the following ions has 12 protons and 10 electrons?

Accepted Answer

$$\mathrm{Mg$$^{2+}$$}$$

Question 13

How many electrons are in a bromide ion ($$\mathrm{Br^-}) if $$the atomic number of bromine is 35?

Accepted Answer

$$36$$

Question 14

Which of the following pairs of ions have the same number of electrons?

Accepted Answer

$$\mathrm{Cl^-}$$ 	ext{ and } \mathrm{Br^-}$

Question 15

A sample of gallium contains 60.11% $$\mathrm{Ga}-69 ($$mass 68.9256 amu) and 39.89% $$\mathrm{Ga}-71 ($$mass 70.9247 amu). What is the atomic mass of gallium?

Accepted Answer

$$69.72\ \mathrm{amu}$$

Question 16

Which isotope of strontium is most abundant if the atomic mass of strontium is 87.62 amu?

Accepted Answer

Sr-88 with a mass of 87.9056 amu

Question 17

Which of the following best describes isotopes?

Accepted Answer

Atoms of the same element with different numbers of neutrons

Question 18

A radioactive isotope is used in medical imaging to diagnose disease. Which property makes it suitable for this application?

Accepted Answer

It emits detectable radiation that can be traced inside the body.

Question 19

Calculate the atomic mass of a hypothetical element Hy with three isotopes: Hy-299 (5.00%, 299.0 amu), Hy-300 (65.00%, 300.0 amu), and Hy-301 (30.00%, 301.0 amu).

Accepted Answer

$$0.05 	imes 299.0 + 0.65 	imes 300.0 + 0.30 	imes 301.0 = 299.75 + 195.0 + 90.3 = 300.3\ \mathrm{amu}$$

Atoms and Elements: Foundations of Modern Chemistry

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