Q: What is the maximum number of electrons that can occupy the third principal energy level (n=3) in an atom?

$$2n^2 = 2$$ \times $$3^2 = 18$

Question 1

Which scientist is credited with the discovery of the electron, and what experiment led to this discovery?

Accepted Answer

J.J. Thomson; cathode ray tube experiment

Question 2

What is the maximum number of electrons that can occupy the third principal energy level (n=3) in an atom?

Accepted Answer

$$2n^2 = 2$$ 	imes $$3^2 = 18$

Question 3

A neutral atom of sodium (Na) has an atomic number of 11. How many valence electrons does it have?

Accepted Answer

1

Question 4

Which of the following best describes an isotope?

Accepted Answer

Atoms with the same number of protons but different numbers of neutrons

Question 5

How many neutrons are present in the nucleus of $$^{235}_{92}U$$?

Accepted Answer

$$235 - 92 = 143$$

Question 6

Which of the following statements about Rutherford’s gold foil experiment is correct?

Accepted Answer

It showed that the atom is mostly empty space with a small, dense, positively charged nucleus.

Question 7

Which group in the periodic table contains elements with the valence electron configuration $$ns^2np^5$?

Accepted Answer

Halogens

Question 8

Which of the following best describes a cation?

Accepted Answer

An atom or group of atoms with a positive charge

Question 9

Which scientist determined the charge of the electron using the oil drop experiment?

Accepted Answer

Robert Millikan

Question 10

What is the electron configuration for a neutral fluorine atom (atomic number 9)?

Accepted Answer

$$1s^2$$ $$2s^2$$ $$2p^5$$

Question 11

Which of the following is a property of metals?

Accepted Answer

Malleable and shiny

Question 12

Which of the following best explains why helium atoms are about four times as massive as hydrogen atoms, even though helium has only twice as many protons?

Accepted Answer

Helium atoms contain two neutrons in addition to two protons.

Question 13

Which of the following statements about the Bohr model of the atom is correct?

Accepted Answer

Electrons emit or absorb quanta of energy when transitioning between energy levels.

Question 14

Which of the following is the correct order of filling for electron sublevels according to the Aufbau principle?

Accepted Answer

$$1s \rightarrow 2s \rightarrow 2p \rightarrow 3s \rightarrow 3p \rightarrow 4s \rightarrow 3d$$

Question 15

Which of the following elements is a metalloid?

Accepted Answer

Silicon

Question 16

A sample of an unknown element is tested in a flame and produces a bright red color. Which element is most likely present?

Accepted Answer

Lithium

Question 17

Which of the following best describes the quantum model of the atom?

Accepted Answer

Electrons are found in regions of high probability called orbitals.

Question 18

Which scientist discovered X-rays while experimenting with cathode ray tubes?

Accepted Answer

Wilhelm Roentgen

Question 19

Which of the following is the correct electron configuration for magnesium (atomic number 12)?

Accepted Answer

$$1s^2$$ $$2s^2$$ $$2p^6$$ $$3s^2$$

Question 20

Which of the following best describes the difference between an anion and a cation?

Accepted Answer

An anion is negatively charged and a cation is positively charged.

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