Question

Moving from left to right across a row of the periodic table, which of the following values increases by exactly one from element to element?
A. Isotope number
B. Atomic number
C. Atomic mass unit
D. Mass number

Answer 1

Moving left to right across a row of the periodic table, $\boxed{{\text{B}}{\text{. atomic number}}}$ increases by exactly one from element to element.

Further Explanation:

Periodic table:

A systematic arrangement of elements in various rows and columns is known as a periodic table. Here, elements are arranged in increasing order of their respective atomic numbers so that elements with the same chemical and physical properties lie in the same group. Horizontal rows are called periods and vertical columns are called groups. There are 18 groups and 7 periods in a periodic table.

Elements are further classified as metals, non-metals, and metalloids in the periodic table. The elements placed at the left side of the table are called metals and the elements placed at the right of the table are called non-metals. Metalloids are the elements kept between metals and non-metals.

Atomic number is equal to the number of protons present in the nucleus of the atom. In the periodic table, elements are arranged in the increasing order of their atomic numbers so the atomic number increases by exact one unit while moving from left to right in a row.

Atomic mass is the total number of nucleons (protons and neutrons) within the atomic nucleus. It is also known as the mass number. Boron and carbon lie in the same period of the periodic table. Carbon is present to the right of boron. But the mass number of B is 10.8 g while that of C is 12 g. So the mass number does not increase by exactly one unit while moving from left to right in a row.

Atomic mass unit (AMU) is defined as 1/12th mass of a carbon-12 atom. It is used to indicate relative masses of various isotopes. It also does not increase by one unit from left to right in a row.

Atoms of the same element with the same atomic number but different mass numbers are called isotopes. These have the same number of protons but the number of neutrons is different. Isotope number is calculated by the subtraction of number of neutrons and number of protons. It is dependent on both the atomic number and the mass number. As the mass number does not increase by one unit from left to right, isotope number cannot increase by exactly one unit in a row.

Therefore option B is the correct answer.

Learn more:

1. Which ion was formed by providing the second ionization energy? brainly.com/question/1398705

2. Write a chemical equation representing the first ionization energy for lithium: brainly.com/question/5880605

Answer details:

Grade: High School

Subject: Chemistry

Chapter: Periodic classification of elements

Keywords: periodic table, systematic arrangement, elements, groups, periods, atomic number, isotope number, atomic mass unit, mass number, carbon-12, 12 g, neutrons, protons, nucleons, atomic mass.

Answer 2

The periodic table is an arrangement of the chemical elements found in nature. These elements are ordered by their atomic number, the configuration of their electrons as well as their chemical properties.

The current periodic table has 115 elements listed in 7 periods and 10 groups.
Moving from from left to right across a row of the periodic table, the atomic number increases by exactly one from element to element.