Question 36 - Chemical and Physical Foundations of Biological Systems Practice Test for the MCAT

Which of the following pairs of elements has the same number of electrons on its valence layer? (See attachment.)

The IUPAC notation for representing an atom is \(^A_ZX\), where A is the mass number (number of protons + neutrons), Z is the atomic number (number of protons), and X is the element’s chemical symbol. The Z number is often omitted and the number of protons is usually found from the element’s symbol, as all atoms of the same element have the same atomic number.

The periodic table serves as a way of arranging elements based on their increasing atomic numbers. On the periodic table, elements with the same number of electrons in their valence layer are located in the same group (vertical row), and elements with the same principal energy level of their valence layer are located in the same period (horizontal row). The periodic table is shown in the image below:


The location of an element in the periodic table influences its properties. Among the most important periodic trends are ionization energy, which increases from left to right and from bottom to top; atomic radius, which increases from right to left and from top to bottom; and electron affinity, which increases from left to right and from bottom to top.

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