In periodic trends, how does the atomic mass of the first 30 elements in the periodic table generally change as the atomic number increases?

Introduction / Context:
Understanding how atomic mass changes with atomic number is a key part of learning the structure of the periodic table. The first 30 elements, from hydrogen to zinc, provide a good sample for seeing general trends. Atomic mass is the weighted average mass of an element isotopes, measured in atomic mass units. This question asks you to identify the overall pattern in atomic mass for the first 30 elements as their atomic number increases.

Given Data / Assumptions:
- The first 30 elements range from hydrogen (atomic number 1) to zinc (atomic number 30). - Atomic number counts the number of protons in the nucleus. - Atomic mass depends on the total number of protons and neutrons, and on isotopic abundances. - We are looking for the general trend, not small irregular variations.

Concept / Approach:
In the periodic table, as atomic number increases, each successive element has an additional proton and typically one or more additional neutrons. As a result, the atomic mass generally increases with atomic number. There can be minor irregularities due to isotopes and binding energy differences, but these do not reverse the overall upward trend. When you examine the list of the first 30 elements, you see that hydrogen has the smallest atomic mass, and heavy elements like zinc have much larger atomic masses.

Step-by-Step Solution:
Step 1: Consider the starting point. Hydrogen (atomic number 1) has an atomic mass close to 1 atomic mass unit. Step 2: Move to helium (atomic number 2), which has an atomic mass near 4 units, already larger than hydrogen. Step 3: Continue along the sequence: lithium, beryllium, boron, carbon, nitrogen, oxygen and so on. Each new element generally has a larger atomic mass than the previous one. Step 4: By the time you reach elements like calcium, iron, and zinc, their atomic masses are many times greater than that of hydrogen. Step 5: Note that there may be small deviations in how much the mass increases from one element to the next, but there is no systematic decrease in mass as atomic number grows. Step 6: Conclude that the overall pattern for the first 30 elements is that atomic mass generally increases as atomic number increases.

Verification / Alternative check:
You can verify this trend by looking at any periodic table that lists approximate atomic masses beneath each element symbol. Starting at hydrogen and moving step by step to zinc, you will see the numbers rising from about 1 to values around 65 for zinc. Although isotopic composition sometimes creates slight irregularities in exact values, these never change the basic rule that atomic mass becomes larger as atomic number increases across this range. This confirms that a general increase is the correct description.

Why Other Options Are Wrong:
Option B claims that atomic mass decreases as atomic number increases, which contradicts observations because heavier elements have more nucleons. Option C suggests that atomic mass stays exactly the same for all first 30 elements, which is clearly false since hydrogen and zinc differ greatly in mass. Option D states that atomic mass changes randomly with no trend, but periodic tables and nuclear physics both show a clear overall increase tied to adding protons and neutrons.

Common Pitfalls:
Some learners focus too much on minor irregularities, such as cases where the increase in mass from one element to the next is small, and mistakenly think there is no pattern. Others confuse atomic number with atomic mass and think they have no relationship. To avoid confusion, remember that atomic number counts protons and that heavier elements usually also carry more neutrons, so the mass naturally increases as you progress through the periodic table.

Final Answer:
The correct answer is: Atomic mass generally increases as atomic number increases across the first 30 elements.