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

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

Question 1

Which of the following statements best describes the modern atomic theory?

Accepted Answer

Chemical reactions change only the way atoms are combined in compounds, not the atoms themselves.

Question 2

A neutral atom of phosphorus has an atomic number $Z = 15$ and a mass number $A = 31$. How many neutrons does it have?

Accepted Answer

$16$ neutrons

Question 3

Which of the following is the correct electron configuration for magnesium ($Z = 12$)?

Accepted Answer

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

Question 4

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

Accepted Answer

$69.7$ amu

Question 5

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

Accepted Answer

Group 1A (Alkali metals)

Question 6

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

Accepted Answer

$ns^2 np^4$

Question 7

Which of the following statements about isotopes is correct?

Accepted Answer

Isotopes of an element have identical atomic numbers but different mass numbers.

Question 8

Which of the following best describes a metalloid?

Accepted Answer

An element whose properties are intermediate between those of metals and nonmetals.

Question 9

A tin atom ($Z = 50$) has electrons distributed in shells as follows: 2, 8, 18, 18, 4. How many valence electrons does tin have?

Accepted Answer

$4$

Question 10

Which of the following is the correct symbol for the isotope of platinum with 78 protons and 116 neutrons?

Accepted Answer

$^{194}_{78}Pt$

Question 11

Which of the following elements is a noble gas and is known for its lack of chemical reactivity?

Accepted Answer

Argon

Question 12

What is the maximum number of electrons that can be held in the third shell of an atom?

Accepted Answer

$18$

Question 13

Which of the following best explains why electrons fill the lowest energy orbitals first?

Accepted Answer

Because lower energy orbitals are closer to the nucleus and more stable.

Question 14

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

Accepted Answer

The symbol with five dots, one on each side and one paired.

Question 15

Which of the following elements is classified as a transition metal?

Accepted Answer

Nickel

Question 16

If an atom has 14 electrons, with its first and second shells filled and four electrons in its third shell, what is the element?

Accepted Answer

Silicon

Question 17

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

Accepted Answer

Elements in the same group have similar electron configurations in their valence shells.

Question 18

Which of the following is the correct formula for calculating the atomic weight of an element with multiple isotopes?

Accepted Answer

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

Question 19

Which of the following best describes the location and properties of nonmetals on the periodic table?

Accepted Answer

Nonmetals are found on the upper-right side and are poor conductors of heat and electricity.

Atoms and the Periodic Table: Foundations of GOB Chemistry

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