Configuration, the periodic table and properties

The periodic table is like a bookcase: each row is a period and each column is a group, as shown in the figure.

Explain what the electron configurations of elements in the same group have in common and what information the period number gives about the configuration of an element.

The aluminium in drink cans has the electron configuration $1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^1$.

1. a) Which period of the table is it in? (Hint: look at the highest level containing electrons.)
2. b) How many valence electrons does it have?
3. c) Aluminium is in group $13$: what relationship do you observe between this group number and the valence electrons?

Lithium ($Z = 3$) and sodium ($Z = 11$) are alkali metals so reactive that in the laboratory they are stored submerged in oil so that they do not touch the air.

1. a) Write the electron configuration of each.
2. b) Point out what their valence shells have in common and which group of the table they are in.

Match heads contain sulfur, whose electron configuration is $1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^4$.

1. a) Deduce which period and group of the table sulfur is in.
2. b) How many electrons does it need to complete its outermost level?
3. c) Predict which ion it will form and state its charge.

The fluorine ($Z = 9$) in some toothpastes and the chlorine ($Z = 17$) in swimming pools belong to group $17$, the halogens.

1. a) Write the electron configurations of the two elements.
2. b) Explain, based on these configurations, why they are in the same group.

An element is located in group $2$ and period $3$ of the periodic table.

1. a) Write its electron configuration.
2. b) Which element is it? (Hint: it burns with a very intense white light and is used in flares and fireworks.)
3. c) Predict the ion it forms easily and write its symbol with the corresponding charge.

Aluminium (group $13$) and chlorine (group $17$) form the compound $\text{AlCl}_3$, present in some antiperspirants.

1. a) Predict the ion formed by each element, reasoning from their valence electrons.
2. b) Using the charges of these ions, explain why the formula is $\text{AlCl}_3$ and not $\text{AlCl}$.

Sodium and chlorine are in period $3$, but the sodium atom is significantly larger than the chlorine atom, as shown in the figure.

1. a) Write the electron configurations of the two elements and check that their valence electrons occupy the same level.
2. b) Explain why the chlorine atom is smaller, comparing the number of protons attracting that electron shell in each case.

An element X has the electron configuration $1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^6\ 4s^1$.

1. a) Identify it using the periodic table and deduce its period and group.
2. b) Is it a metal or a non-metal? Which ion will it easily form?
3. c) Predict the formula of the compound it forms with oxygen, which gives $\text{O}^{2-}$ ions, and justify your answer.

The radius of the sodium atom is about $0,190\ \text{nm}$, whereas that of its $\text{Na}^+$ ion is only $0,098\ \text{nm}$. In contrast, the chlorine atom measures $0,099\ \text{nm}$ and its $\text{Cl}^-$ ion measures $0,181\ \text{nm}$, as shown in the diagram.

1. a) State how the size of each element changes when it becomes an ion.
2. b) Explain both changes by comparing the number of protons and electrons before and after the ions are formed (you may use electron configurations to help you).