Question

1. choose the best answer.

atomic masses ___ across a period and ___ down the periodic table.
decrease; increase
increase; increase
decrease; decrease
increase; decrease

1. choose the best answer.

_____ model was used to help mendeleev and meyer construct the periodic table.
bohrs
rutherfords
the plum pudding
daltons

Explanation:

Question 15

As we move across a period (from left to right) in the periodic table, the atomic number increases. Since atomic mass is related to the number of protons, neutrons (and electrons, but their mass is negligible). As the atomic number (number of protons) increases, and generally the number of neutrons also increases in a non - systematic but overall increasing way across a period. When we move down a group (top to bottom), new electron shells are added. Each new shell has more protons, neutrons (and electrons). So, atomic masses increase across a period and increase down the periodic table.

• Bohr's model: Proposed in 1913, long after Mendeleev (1869) and Meyer (1864 - 1870) constructed the periodic table.
• Rutherford's model: Proposed in 1911 (gold foil experiment), after Mendeleev and Meyer's work.
• Plum - pudding model: Proposed by J.J. Thomson in 1904, after Mendeleev and Meyer's work.
• Dalton's model: Dalton's atomic theory (1808) stated that atoms of different elements have different masses. This was a foundational concept that Mendeleev and Meyer could have used. For example, Mendeleev arranged elements in order of increasing atomic mass (a concept related to Dalton's atomic theory where atoms of different elements have different properties including mass)

Answer:

increase; increase

Question 16