Periodic Table: Answers

If an element is found in group 4 of the Periodic Table, how many outer electrons does it have?

Short answer: 4

Long answer: The Periodic Table is arranged in columns, numbered 1 to 8 and the group number is the same as the number of electrons in the outer shell of the atom. This means that all of the elements which are found in group 4 (carbon, silicon, germanium etc) will all have four outer electrons. The number of outer shell electrons determines how a particular element behaves in a chemical reaction. This means that the group 4 elements will all react in similar ways and show similar properties.

State the maximum number of electrons that can be held in the first three electron shells.

A maximum of 2 electrons can be held in the innermost shell then 8 in the second and third shell. If you don’t already know this make sure you learn it because it will be sure to come up in your exam.

Give the electron configuration of aluminium.

Short answer: 2,8,3

Long answer: By looking at the Periodic Table we can see that aluminium has an atomic number of 13, so we know there are 13 protons in its nucleus. The number of protons is always equal to the number of electrons (in a neutral atom), so we also know that aluminium has 13 electrons. The first electron shell is only able to hold 2 electrons, while the second can hold 8. By this point we’ve accounted for ten electrons, so we only have three remaining which will all be in the third shell. The electron configuration for aluminium is 2,8,3.

Explain the difference between a ‘group’ and a ‘period’.

A group is a vertical column within the Periodic Table whereas a period is a horizontal row. If you go down the group (e.g. from lithium, sodium, potassium etc) you gain a whole extra electron shell from one element to the next. If you go across a period (e.g. from lithium, beryllium, boron, carbon etc), you gain just one electron as you go from one element to the next.

Which element has the electron configuration 2,8,5?

Short answer: phosphorus

Long answer: there are a few ways to work this out so choose whichever works for you and stick with it. Probably the simplest is to count the total number of electrons and look for the element with the same atomic number on the Periodic Table. Here we have a total of 15 electrons and element no. 15 on the Periodic Table is phosphorus. Another way is to see how many numbers we have separated by commas, which tells us which period the element will be found in. Here we have three numbers separated by commas so the element must be in period 3. Then you look at the last number to tell you the group that the element is in. Here the last number is five, so we know that the element is in period 3 and group 5.

Compare the properties of metals and non-metals.

Metals can conduct electricity whereas non-metals can’t. Metal oxides act as bases (they remove hydrogen ions from a solution) whereas non-metal oxides act as acids (they add hydrogen ions to a solution).

Where are metals placed on the Periodic Table?

Short answer: on the left hand side

Long answer: if you draw an imaginary diagonal line starting from boron and passing through silicon until you reach astatine, then the metals will be found to the left of this line and actually make up the majority of all elements on Earth. There are much fewer non-metals, which are found in the top right hand corner. The elements lying on your imaginary line are called ‘metalloids’ and have properties of both metals and non-metals.