Q: Which of the following is the correct formula for calculating the atomic weight of an element from its isotopes?

$\text{Atomic weight} = \sum[(\text{isotopic abundance}) \times (\text{isotopic mass})]$

Question 1

Which of the following statements is NOT one of the four main postulates of atomic theory as described in the study materials?

Accepted Answer

Atoms of the same element can have different numbers of protons.

Question 2

A neutral atom of phosphorus has a mass number of 31. How many neutrons does it contain?

Accepted Answer

16

Question 3

Which subatomic particle has a mass approximately $1/1836$ that of a proton and carries a negative charge?

Accepted Answer

Electron

Question 4

Gallium has two naturally occurring isotopes: $^{69}\mathrm{Ga}$ (60.4% abundance, mass = 68.9257 amu) and $^{71}\mathrm{Ga}$ (39.6% abundance, mass = 70.9248 amu). What is the atomic weight of gallium? (Round to one decimal place)

Accepted Answer

$69.7$ amu

Question 5

Which group of the periodic table contains elements that are shiny, soft metals with low melting points and react vigorously with water?

Accepted Answer

Group 1A (Alkali metals)

Question 6

Which of the following elements is classified as a metalloid based on its position in the periodic table?

Accepted Answer

Silicon (Si)

Question 7

An atom has its first and second shells filled and has four electrons in its third shell. What is the atomic number and identity of this element?

Accepted Answer

Z = 14, Silicon (Si)

Question 8

Which of the following electron configurations represents chlorine (Cl)?

Accepted Answer

$1s^22s^22p^63s^23p^5$

Question 9

Which of the following best describes the electron configuration for magnesium (Mg)?

Accepted Answer

$1s^22s^22p^63s^2$

Question 10

Which of the following elements has the electron configuration $[Kr] 5s^24d^2$?

Accepted Answer

Zirconium (Zr)

Question 11

What is the general valence-shell electron configuration for elements in group 6A?

Accepted Answer

$ns^2np^4$

Question 12

Which of the following statements about noble gases is TRUE?

Accepted Answer

They are colorless gases with very low chemical reactivity.

Question 13

A platinum isotope is represented as $^{194}_{78}\mathrm{Pt}$. How many neutrons does this isotope contain?

Accepted Answer

116

Question 14

Which of the following is the correct electron-dot (Lewis) symbol for an element in group 5A?

Accepted Answer

The atomic symbol with five dots arranged around it, with one pair and three single dots.

Question 15

Which of the following best explains why alkali metals are never found in nature in a pure state?

Accepted Answer

They are highly reactive and readily combine with other elements.

Question 16

Which of the following statements about electron shells and subshells is correct?

Accepted Answer

The farther a shell is from the nucleus, the more electrons it can hold.

Question 17

Which element has 50 electrons, with 4 valence electrons in the 5s and 5p subshells?

Accepted Answer

Tin (Sn)

Question 18

Which of the following is the correct formula for calculating the atomic weight of an element from its isotopes?

Accepted Answer

$	ext{Atomic weight} = \sum[(	ext{isotopic abundance}) 	imes (	ext{isotopic mass})]$

Question 19

Which of the following best describes the difference between a transition metal and a main group element?

Accepted Answer

Transition metals have partially filled d subshells, while main group elements fill s and p subshells.

Atoms and the Periodic Table: Fundamentals for GOB Chemistry

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