Video Transcript
In this video, we will learn how to
identify and name the alkali metals, describe their physical properties, and explain
their chemical activity. The periodic table has elements
organized by periods, which go from left to right, and groups, which are positioned
from top to bottom, like a column. In this video, we will focus on the
group one metal elements.
Alkali metals are metal elements in
the leftmost group of the periodic table. These alkali metals include
lithium, Li; sodium, Na; potassium, K; rubidium, Rb; cesium, Cs; and francium,
Fr. It should be noted that hydrogen,
H, which is above lithium, is not an alkali metal even though it is in the leftmost
group of the periodic table since it is classified as a nonmetal. Now that we have identified the
alkali metals within the periodic table, let us discuss some of their chemical
properties.
One chemical property of alkali
metals is that they all react with water and form an alkaline solution. For example, solid lithium reacts
with water. This violent reaction creates
lithium hydroxide, which is the alkaline solution, and hydrogen gas. Since this reaction creates an
alkaline solution due to the hydroxide ions, chemists call group one elements the
alkali metals. In order for us to understand why
this chemical reaction occurs within alkali metals, let us investigate the electron
shell of these metals.
All alkali metals have one valence
electron. When an alkali metal undergoes a
chemical reaction, the one electron in the outer electron shell leaves the alkali
metal and is transferred to the outer electron shell of the nonmetal, such as
fluorine. When this occurs, the lithium atom
becomes a lithium ion with a charge of one plus since it lost one electron. Since the fluorine atom gained one
electron, it becomes a fluoride ion with a charge of one minus. This makes the lithium and fluoride
ions more stable and less likely to react.
Now that we have discussed how
alkali metals form compounds, let us move on to the physical properties of these
metals. Since these alkali metals can
readily react with water vapor in the air, chemists usually store the solid alkali
metals in containers with kerosene to prevent them from reacting. When observing the alkali metals,
lithium has the lowest density of all alkali metals and floats in kerosene. When this occurs, it can
tarnish. This is why lithium is usually kept
in paraffin wax. When identifying lithium within the
group of alkali metals, it is at the top of the group and has the lowest
density.
As we go down the alkali metal
group, we should note that the density generally increases. It should be noted that potassium
has a lower density compared to both sodium and rubidium. In general, alkali metals have a
lower density compared to other metals. When these alkali metals are taken
out of the kerosene or paraffin wax, this is when a reaction occurs. But do all the alkali metals have
the same reactivity? If we consider that this image
represents a reaction of francium, then the answer would be no. Since lithium is less reactive
compared to francium, reactivity of the alkali metals increases going down the group
of these metals.
Alkali metals also have additional
practical physical properties. For instance, they are good
conductors of heat and electricity. An example of this is when liquid
sodium is used in nuclear reactors to absorb and transfer the heat from inside the
reactor to outside. Alkali metals also tend to be
malleable, meaning they can be hammered into a thin sheet without breaking. They also have low melting and
boiling points compared to other metals within the periodic table. In general, the melting and boiling
points tend to decrease down the group of alkali metals. Finally, these metals are dull on
the outside because they have reacted with the oxygen or water vapor in the air. However, when they are cut, the
inside is shiny or has a luster since it has not been exposed to the air.
Now, let us have some practice.
In which of the following images of
the periodic table has the alkali metal group been correctly highlighted?
This question is asking us to
identify which group in the periodic table represents the alkali metals. A group on the periodic table is a
set of elements that form a column. All of the shaded areas in the
images given represent a group. Before we begin to answer this
question, let us now discuss alkali metals. An alkali metal is any metal
element in the leftmost group of the periodic table. The alkali metal group consists of
six elements: Li, lithium; Na, sodium; K, potassium; Rb, rubidium; Cs, cesium; and
Fr, francium. Above this group of elements is
hydrogen, which is not classified as an alkali metal since it is a nonmetal.
Looking back at our answer choices,
we should notice that option choice (A) has the group highlighted that is to the
leftmost side of the periodic table. In conclusion, answer choice (A) is
the image of the periodic table that has the alkali metal group correctly
highlighted.
Now, let us try another
question.
Which of the following is not a
property of the alkali metals? (A) Being chemically inactive, (B)
looking shiny when cut, (C) good conductivity of electricity, (D) good conductivity
of heat, (E) malleability.
This question is asking us to
identify which of the listed options is not a property of the alkali metals. An alkali metal is any metal
element in the leftmost group of the periodic table. The six alkali metals are lithium,
sodium, potassium, rubidium, cesium, and francium. Now that we have identified the
alkali metals, let us discuss some properties pertaining to this group of
metals.
Alkali metals usually look dull
because they easily react with the water vapor in the air. While these elements may look dull
on the outside, when these elements are cut, the inside has a shiny luster to
them. This group of elements are also
good conductors of heat and electricity. A good example of this is with
lithium. That element is used to make
batteries within your cell phone. Finally, these elements can be
hammered into thin sheets; therefore, they demonstrate malleability.
In order to correctly answer this
question, we need to identify which option is not a property of alkali metals. When comparing the properties of
alkali metals, the property that is not represented is being chemically inactive
since alkali metals are reactive. For example, they react readily
with water vapor in the air. Therefore, the correct answer
choice is (A). Being chemically inactive is not a
property of the alkali metals.
Now, let us try another problem
related to alkali metals.
The image below shows the elements
of the alkali metal group. Which element in this group can be
considered the most reactive towards water? Give your answer using the
element’s symbol.
This question is asking us to
identify the alkali metal that is most reactive in water. Let us first rearrange these
elements based upon how they would appear on the periodic table. When an alkali metal such as sodium
reacts with water, hydrogen gas and sodium hydroxide form. While all alkali metals react with
water, their reactivities are not the same. Within the alkali metal group of
the periodic table, there is a pattern to chemical reactivity that begins with
lithium being the least reactive metal within the group. Going down the group of alkali
metals, the reactivity increases. Therefore, the most reactive alkali
metal with water would be cesium. In conclusion, the alkali metal
that can be considered the most reactive towards water is Cs.
Now, let us review our final
question.
What type of solution is formed
when the metal elements of group one react with water? (A) Acidic, (B) neutral, or (C)
alkaline.
Since this question is asking us to
name the solution formed when a group one element reacts with water, let us first
identify these elements. Group one elements are also known
as alkali metals. An alkali metal is any metal
element in the leftmost group of the periodic table. Alkali metals are this set of six
metal elements: lithium, sodium, potassium, rubidium, cesium, and francium. When an alkali metal, such as
potassium, reacts with water, a chemical reaction occurs. The reaction produces potassium
hydroxide and hydrogen gas. The potassium hydroxide that forms
is classified as an alkaline solution, hence the reason group one elements are
labeled as alkali metals. When looking back at this question,
the type of solution that is formed when elements of group one react with water is
alkaline, or answer choice (C).
Now that we have reviewed a few
examples, let us summarize the key points of alkali metals. Alkali metals form group one of the
periodic table. This set of elements are lithium,
sodium, potassium, rubidium, cesium, and francium. Alkali metals react with water and
form alkaline solutions. The reason alkali metals can react
with water is because they have one valence electron. Chemical reactivity increases going
down the group of alkali metals. Alkali metals can have physical
properties such as having lower densities, melting points, and boiling points
compared to other metals. Finally, alkali metals can conduct
heat and electricity, have luster when cut, and are malleable.
