Group 3A

Group 3a Elements

Let's start by looking at the definition of group 3A elements.

Because they are in the 13th column, they are also called group 13. They are also called the "boron family" since they start with boron, as shown below:

Fig.1-Group 3A location on periodic table

This group is different from group 3, which is the third column of the periodic table. This is the first column of transition metals. Group 3A is the third column across when you skip the transition metals.

The group 3A elements in order are:

• Boron (B): Element 5

• Aluminum (Al): Element 13

• Gallium (Ga): Element 31

• Indium (In): Element 49

• Thallium (Tl): Element 81

There is another element in this group called nihonium (Nh). It is man-made, and the small amounts of it that were made decayed in seconds. While it is calculated to have properties similar to group 3A elements, not enough is known about it to be thoroughly talked about.

Group 3A Electron Configuration

Let's first talk about each element's Electron Configuration, since they will give us some insight on some of each element's properties.

Below is each group 3A element's electron configuration:

The Valence Electrons are highlighted in blue.

All 3A electrons have 3 valence electrons, which is why they are often referred to as "group 3A" instead of group 13.

Physical Properties of Group 3A Elements

There are clear trends in the physical properties of this group. However, boron is often an outlier. Boron, unlike the other 3A elements, is a metalloid, which shares properties of non-metals and metals. The other group 3A elements are metals.

Here are some common properties of group 3A elements:

• Soft, silver/grey metals

  • Boron is brittle and is either a dark crystal or brown powder

For comparison, here is what boron and thallium look like:

Fig.2 Comparing boron to thallium

• Good conductors of electricity

  • Boron is a good conductor at high temps, but it as an insulator (poor conductor) at room temp

• Low melting/boiling points

  • Boron's has a significantly higher boiling point than the other group 3a elements

As you can see, since Boron is a metalloid, its properties are somewhat unlike the other group 3A elements, however, as you'll see later, it's reactivity "falls in line" with most or all of the other elements in the group.

Trends in Physical Properties' Table

Another way we can characterize the physical properties of a group is by looking at how these properties change for element to element. Let's look at some different properties and their trends across the group:

Boiling point

As you go down the group, boiling point decreases

-There is a sharp decrease between boron and aluminum

Atomic radius (distance between center of nucleus and outermost electron(s))Atomic radius increases as you move down the group. However, Aluminum is larger than gallium. This is because gallium has d-electrons, which do a poor job of "shielding" the attractive force of the nucleus from other electrons. Because of this, the attractive force of the nucleus is stronger, meaning the electrons will be held more closely, causing the radius to be smaller.

Think of it like putting pieces of paper in between two magnets. The paper "shields" the magnets from each other, so the attractive force is weakened. However, if there are fewer sheets of paper, the attractive force is stronger. Electronegativity (the tendency to attract/gain electrons)Electronegativity decreases as you move down the table. The order of most to least electronegative is:

boron > gallium > indium > thallium > aluminum

Chemical Properties of Group 3a Elements

All the group 3A elements have a +3 oxidation state, except thallium, which has a +1 oxidation state.

In this case, that means most 3A elements will lose 3 electrons, meaning they lose all of their valence electrons. This means that they have a new and complete "set" of valence electrons (i.e. the electrons in the energy level below the highest are now the highest energy level).

Thallium only loses one electron, so it will have a full 6s-orbital.

Because boron is a metalloid, it forms mainly covalent bonds, which are bonds where the electrons are shared between two non-metals or a non-metal + metalloid. However, the other group 3A elements usually form ionic bonds. These are bonds where one element donates electrons to another element.

Group 3A Reactions and Compounds

The group 3A elements have a common set of compounds they produce, let's walk through some of them

Oxides

All group 3A's elements are able to react with oxygen gas (O₂), as shown below:

$$G_{(s)} + O_{2\,(g)} \rightarrow G_2O_3$$

Where "G" is a group 3A element. However, thallium is the exception, since it forms TlO₂ because of it's +1 oxidation state (oxygen has a -2 oxidation state).

Nitrogen

Except for thallium, all group 3A elements react with Nitrogen gas (N₂) as shown below:

$$G_{(s)} + N_{2\,(g)} \rightarrow GN$$

Where "G" is a group 3A element. Nitrogen has a -3 oxidation state, which is why the ratio is 1:1.

Halides

The last type of reaction we are going to talk about is with the halides (group 17). Like with the oxides, all the halide compounds follow a similar formula, except for thallium.

Below is a general group 3A halide reaction:

$$G_{(s)} + X_{2\,(g)} \rightarrow GX_3$$

Where "G" is a group 3A element and "X" is a halide (ex: Cl₂, Br₂, etc.). Halides have a -1 oxidation state, which is why the general form is GX₃, but thallium forms TlX.

Group 3A Characteristics

As a summary of what we've learned, here are the group 3A characteristics:

• Metals

  • Except for boron, which is a metalloid

• Good conductors

  • Boron only at high temps

• Low melting/boiling points

  • Except for boron

• Have 3 valence electrons

• Have a +3 oxidation state

  • except for thallium, which has a +1 state

• Will react with oxygen gas, nitrogen gas, and halides

  • Thallium will not react with nitrogen gas