Question 1

Which experiment led to the discovery of the atomic nucleus, and what was the main conclusion drawn from it?

Accepted Answer

Rutherford’s gold foil experiment; atoms have a dense, positively charged nucleus.

Question 2

A neutral atom of chlorine has an atomic number of 17 and a mass number of 35. How many neutrons does it contain?

Accepted Answer

$$35 - 17 = 18$$ neutrons

Question 3

Which of the following statements best describes isotopes?

Accepted Answer

Isotopes have the same number of protons but different numbers of neutrons.

Question 4

How many electrons are present in an $$\mathrm{O}^{2-}$$ ion?

Accepted Answer

10

Question 5

Which property is most characteristic of metals in the periodic table?

Accepted Answer

They are malleable and ductile.

Question 6

Which group in the periodic table contains elements that are highly unreactive and chemically stable?

Accepted Answer

Group 8A (Noble gases)

Question 7

A main-group metal forms a cation by losing electrons. Which noble gas configuration does a sodium ion ($$\mathrm{Na}^+) $$achieve?

Accepted Answer

Neon ($$\mathrm{Ne})$$

Question 8

Which of the following best explains why Mendeleev’s periodic table had gaps?

Accepted Answer

He left gaps for elements that had not yet been discovered, predicting their properties.

Question 9

Which element is classified as a metalloid and what property does it exhibit?

Accepted Answer

Silicon; it is a semiconductor with temperature-dependent conductivity.

Question 10

An atom has 18 protons and 22 neutrons. What is its mass number, and which element is it?

Accepted Answer

Mass number $$= 18 + 22 = 40$$; element is Argon ($$\mathrm{Ar})$$

Question 11

Which of the following best describes the periodic law as stated by Mendeleev?

Accepted Answer

When elements are arranged in order of increasing mass, certain sets of properties recur periodically.

Question 12

Which of the following ions has the same number of electrons as a neon atom?

Accepted Answer

$$\mathrm{Na}^+$$

Question 13

Which scientist is credited with the discovery of the neutron, and why was this discovery important?

Accepted Answer

James Chadwick; it explained the missing mass in atoms.

Question 14

Which group of elements tends to gain two electrons to form anions with a $$2-$$ charge?

Accepted Answer

Group 6A (Chalcogens)

Question 15

A sample of neon contains 90.48% $$^{20}\mathrm{Ne}$$, 0.27% $$^{21}\mathrm{Ne}$$, and 9.25% $$^{22}\mathrm{Ne}. $$What does this information describe?

Accepted Answer

The natural abundance of neon isotopes.

Question 16

Which of the following is a correct representation of an isotope of carbon with 6 protons and 8 neutrons?

Accepted Answer

$$^{14}_{6}\mathrm{C}$$

Question 17

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

Accepted Answer

Elements are arranged in order of increasing atomic number.

Question 18

Which property distinguishes transition metals from main-group elements?

Accepted Answer

Their properties are less predictable based on their position in the periodic table.

Question 19

Which of the following best describes the charge and location of a proton in an atom?

Accepted Answer

Positive charge; located in the nucleus.

Question 20

Which of the following best explains why isotopes of the same element have different mass numbers?

Accepted Answer

They have different numbers of neutrons.

Atoms, Elements, and the Periodic Table: Study Notes for General Chemistry

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