Let's analyze each question:
21. A student looks up an element on the periodic table. The table says that the atomic number of the element is 12 and the mass number of the element is 40. What information do these two numbers convey about the element?
- The atomic number (12) indicates the number of protons in the element. Since the element is neutral, this also means it has 12 electrons.
- The mass number (40) is the total number of protons and neutrons. Therefore, to find the number of neutrons, we subtract the number of protons from the mass number: \[ \text{Number of neutrons} = \text{Mass number} - \text{Number of protons} = 40 - 12 = 28 \]
So, the correct answer is: c The element has 12 protons and has 28 neutrons.
22. In all elements in a group, the thing that is the same is the:
In the periodic table, elements in the same group (column) typically have the same number of electrons in their outermost shell, which is known as the valence shell.
So, the correct answer is: a Number of electrons in the valence shell.
23. How many oxygen atoms are in the compound below: Cu3(PO4)2?
First, let's break down the compound:
- The phosphate ion (PO4) contains 4 oxygen atoms.
- There are 2 phosphate ions in the compound, as indicated by the subscript 2 outside the parentheses.
Therefore, the total number of oxygen atoms is: \[ \text{Total oxygen} = 4 , \text{(from PO4)} \times 2 = 8 \]
So, the correct answer is: C) 8.
16 answers