Which description best describes what happens in a period?
Properties of elements gradually change across this category in a predictable way.
Elements in this category have similar chemical and physical properties.
The second description best describes what happens in a period.
The second description best describes what happens in a period. Elements in a period have similar chemical and physical properties.
The description that best fits what happens in a period is: "Properties of elements gradually change across this category in a predictable way."
To understand why this description best describes what happens in a period, you need to have a basic understanding of the periodic table of elements. The periodic table is organized into periods, which are the horizontal rows of elements. Each period represents a different energy level in an atom.
Within a period, the properties of the elements gradually change across the category in a predictable way. This is because the number of electrons in the outermost energy level, also known as the valence electrons, increases by one from left to right within a period. The arrangement of valence electrons determines an element's chemical and physical properties.
As you move from left to right across a period, the elements generally become less metallic and more non-metallic. Metals are typically found on the left side of the periodic table, while non-metals are on the right side. Additionally, the atomic size generally decreases across a period as the positively charged protons in the nucleus attract the negatively charged electrons more strongly.
Therefore, the description "Properties of elements gradually change across this category in a predictable way" accurately captures the trend of changing properties within a period on the periodic table.