Question

Which elements are alkali metals? (a) barium (b) sodium (c) gold (d) tin (e) rubidium

Short answer

Sodium (b) and rubidium (e) are alkali metals.

Step-by-step solution

Understand the Properties of Alkali Metals

Alkali metals are located in group 1 of the periodic table. They have one electron in their outermost shell and are highly reactive, especially with water. They include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr).

Classify Each Element

Look at the list of elements given in the exercise and determine which of them are in group 1 of the periodic table, which is indicative of alkali metals.

Identify Alkali Metals from the List

From the provided list: (a) barium (Ba) is an alkaline earth metal, not an alkali metal; (b) sodium (Na) is an alkali metal; (c) gold (Au) is a transition metal; (d) tin (Sn) is a post-transition metal; and (e) rubidium (Rb) is an alkali metal.

Key concepts

Understanding the Periodic Table

The periodic table is like a big organizational chart for elements. Picture it as a grid where each box represents one of the basic building blocks of everything around us. Elements are arranged by their atomic number (that's the number of protons in the nucleus), and by similar characteristics.

At the very start, on the left-hand side, there's a special group called Group 1. This is where the alkali metals live. They're like a family with shared traits - the main one is they all have a single electron in their outermost shell, which might not sound like a big deal, but it's like having a superpower in the world of chemistry.

Remember, the position of an element in the table can tell you a lot about its behavior. For instance, being in Group 1 tells us that an element is more likely to give up that lone outer electron to join in chemical reactions, making the alkali metals very social in the chemistry world.

The Chemical Properties of Alkali Metals

Alkali metals have some unique chemical properties. As mentioned earlier, their single electron in the outermost shell is the key to understanding their behavior. This electron is like the one piece of luggage that's easy to lose at the airport - it's loosely held and can easily be passed on to other elements.

What's more, these metals are super reactive, particularly with water. Sodium (Na), for example, will dance around and fizz up if you throw it into water. It's this reactivity that makes alkali metals both fascinating and tricky to work with. They also have low melting and boiling points compared to other metals. This means some of them can melt just from the warmth of your hand!

Besides their sensational reactions with water, alkali metals are pretty soft. You could cut them with a knife, though that's not recommended for safety reasons. All these characteristics make alkali metals quite unique from their neighbors on the periodic table.

The Reactivity of Alkali Metals

Now, let's talk about the party trick of the alkali metals: their reactivity. These elements don't like being alone; they prefer to be part of compounds. For example, when you expose them to air, they'll start bonding with oxygen super quickly.

The reactivity of these metals increases as you go down the group. That means while lithium (Li), the lightweight, is pretty reactive, francium (Fr), way down at the bottom, is the life and soul of the chemistry party, reacting with a bang! And because of this reactivity, you rarely find them in nature just chilling by themselves; they're usually in compounds.

Why So Reactive?

Well, it's because losing that one outer electron makes them stable, and elements love stability. The larger the atom (like those further down in Group 1), the further away the outer electron is from the pull of the nucleus, making it even easier to lose. It's a bit like kids moving out when they grow up - the bigger they are, the more likely they are to want their own space, or in this case, join another element.