Video Transcript
An ion has atomic number 29, mass number 65 and a charge of two plus. How many protons does the ion contain?
Generally speaking, an ion is an atom or molecule that has lost or gained electrons. For instance, lithium can form a lithium ion by giving up one electron. The ion in this question has properties of atomic number, mass number, and charge. Atomic number and mass number only apply to single atoms. So this ion must be derived from an atom.
What the question is asking is how many protons there are in the nucleus of this ion. To answer this question, we can fall back on the definition of the atomic number. The atomic number refers to the number of protons in the nucleus of the atom or ion it refers to. In our case, the atomic number of the ion is 29. So this ion contains 29 protons.
How many neutrons does the ion contain?
The mass number of an ion or atom refers to the number of protons plus the number of neutrons in the nucleus. This ion has a mass number of 65. This gives us the equation that the number of protons plus the number of neutrons for this ion is equal to 65.
From part a) we know that the number of protons is equal to the atomic number, which is 29. So the number of neutrons in this ion is equal to 65 minus 29, which is equal to 36.
How many electrons does the ion contain?
The charge of an atom or ion is equal to the number of protons minus the number of electrons. This is because protons have a one plus charge. And electrons have a one minus charge. Since we’re given the charge of this ion, we can work out how many electrons it contains. For this ion, the number of protons minus the number of electrons is equal to two.
As before, we know that number of protons is equal to the atomic number, which is 29. So we can rearrange the equation in terms of the number of electrons to equal 29 minus two, which is equal to 27. We can check that this makes sense by looking at 27 minus and 29 plus, which will have an overall charge of two plus. So we’ve demonstrated that this ion will contain 27 electrons.
What is the chemical symbol for this element?
So this ion has an associated element. And the element has an element symbol. Every element is uniquely identified by its atomic number. In this case, we’re looking for the element with atomic number 29. Where should we look? On our periodic table. The periodic table contains all the known elements and contains much information about them. Each element on the periodic table has its own cell, which contains at the top its atomic number and in the middle its element symbol. So we’re looking for the 29th element, the cell which has 29 at the top. And then we’re going to find the chemical symbol.
If you look at your periodic table, you’ll see the element with atomic number 29 is copper, with the symbol Cu. So the chemical symbol for the element associated with this ion is Cu. If you wanted to, you could represent all the information in this question in nuclide notation like this, where the chemical symbol Cu has the associated atomic number, mass number, and charge.
