The periodic table | Atoms, elements, and the periodic table | High school chemistry | Khan Academy

Summary

This educational video script explores the periodic table's organization, focusing on groups and periods. It explains how elements are classified into groups (vertical columns) and periods (horizontal rows), with groups numbered 1 to 18 and periods 1 to 6. The script highlights alkali metals in group 1A, alkaline earth metals in group 2A, and discusses their reactivity and states in nature. It contrasts metals, typically found on the left side, with nonmetals on the right, and introduces metalloids with properties between the two. The video also touches on halogens and noble gases, setting the stage for further discussions on electronic structure and transition metals.

Takeaways

• 🔍 The periodic table organizes elements into vertical columns called groups, numbered from 1 to 18.
• 📏 Another way to label groups is using A and B categories, such as 1A, 2A, and skipping to 3A for group 13.
• 🔬 The concept of periods refers to the horizontal rows on the periodic table, with elements like hydrogen and helium in the first period.
• 🟥 Alkali metals, found in group 1 or 1A, are soft, silvery, and extremely reactive metals that are never found in their pure state in nature.
• 🟩 Hydrogen, despite being in group 1, is a nonmetal and does not share the same reactivity as alkali metals.
• 🟨 Alkaline earth metals, located in group 2 or 2A, are less reactive than alkali metals but are also found in combination with other elements in nature.
• 🛠 Metals, in general, are malleable and ductile, and they conduct heat and electricity well, with the exception of mercury which is liquid at room temperature.
• 🟦 Nonmetals are typically poor conductors of heat and electricity, and solid nonmetals are brittle rather than malleable.
• 🌐 Halogens, found in group 7A or 17, are very reactive nonmetals known for their corrosive nature and ability to form salts.
• 💨 Noble gases, located in group 8A or 18, are colorless, unreactive gases with complete electron shells making them stable.
• 📏 The periodic table is divided into metals on the left, nonmetals on the right, and metalloids along a zigzag line in between, which have properties of both.

Q & A

What are the groups on the periodic table?

The groups on the periodic table are the vertical columns, numbered from 1 to 18. They are also referred to as groups 1A to 8A, excluding groups 3 through 12.

How are the groups numbered on the periodic table?

Groups on the periodic table can be numbered in two ways: either by simply numbering them 1 to 18, or by using the A system where groups 1 and 2 are called 1A and 2A, and groups 13 to 18 are labeled 3A to 8A.

What is the significance of valence electrons in group numbering?

The second way of numbering groups, using the A system, is useful when considering valence electrons because it helps in understanding the chemical properties and reactivity of elements within the same group.

What is a period on the periodic table?

A period on the periodic table is a horizontal row, with the first period containing hydrogen and helium, and each subsequent period adding more elements.

Why are alkali metals found in group 1 or 1A?

Alkali metals are found in group 1 or 1A because they all have one electron in their outermost shell, which they readily lose to form positive ions, making them highly reactive.

How do alkali metals react with water?

Alkali metals react vigorously with water, often producing a hydrogen gas and an alkaline solution, due to their high reactivity and tendency to lose their single valence electron.

Why are alkali metals not found in their pure state in nature?

Alkali metals are not found in their pure state in nature because of their extreme reactivity. They are typically found combined with other elements in compounds.

What distinguishes hydrogen from other alkali metals?

Hydrogen is in group 1 but is not an alkali metal; it is a nonmetal. This distinction is due to its unique properties and electron configuration, which do not align with the typical characteristics of alkali metals.

What are alkaline earth metals and where are they located on the periodic table?

Alkaline earth metals are found in group 2 or 2A and include elements like magnesium, calcium, and strontium. They are less reactive than alkali metals but share similar chemical properties.

What are the general properties of metals?

Metals are typically solid at room temperature, malleable, ductile, and good conductors of heat and electricity. They are found on the left side of the periodic table.

How are nonmetals different from metals in terms of properties?

Nonmetals are generally poor conductors of heat and electricity, can be brittle, and are found in various states of matter. They are located on the right side of the periodic table.

What are halogens and where can they be found on the periodic table?

Halogens are very reactive nonmetals found in group 7A or 17. They include elements like fluorine, chlorine, and bromine, and are known for their corrosive properties and tendency to form salts.

Why are noble gases unreactive?

Noble gases are unreactive because they have a full valence shell of electrons, making them stable and less likely to form chemical bonds with other elements.

What is the dividing line between metals and nonmetals on the periodic table?

The dividing line between metals and nonmetals on the periodic table is a zigzag line that separates the elements with metallic properties on the left from those with nonmetallic properties on the right.

What are metalloids and which elements are commonly considered metalloids?

Metalloids are elements with properties intermediate between metals and nonmetals. Commonly considered metalloids include boron, silicon, germanium, arsenic, antimony, tellurium, and sometimes astatine.

Why is silicon an important metalloid?

Silicon is an important metalloid because it is a semiconductor, which means it can conduct electricity under certain conditions but not as readily as a metal, making it crucial in electronic devices.

Outlines

00:00

🔬 Introduction to the Periodic Table

This paragraph introduces the concept of the periodic table, focusing on the classification of elements into groups and periods. The groups are the vertical columns, numbered from 1 to 18, with an alternative numbering system that includes letters (1A to 8A). The video script explains how elements within the same group share similar chemical properties, which is why group 1 (or 1A) contains alkali metals like lithium, sodium, and potassium. The paragraph also touches on the concept of periods, which are the horizontal rows on the periodic table, and provides an example of the first two periods, highlighting elements like hydrogen, helium, lithium, and so on. The script emphasizes the importance of understanding group and period classifications for predicting an element's properties.

05:02

🌐 Properties of Metals and Nonmetals

The second paragraph delves into the properties of metals and nonmetals, contrasting their characteristics. Metals, found predominantly on the left side of the periodic table, are described as solid at room temperature (except for mercury), malleable, ductile, and good conductors of heat and electricity. Nonmetals, typically located on the right side, are portrayed as poor conductors of heat and electricity, often found in different states of matter, and can be brittle solids. The paragraph also introduces halogens and noble gases, highlighting their reactivity and unreactivity, respectively. Halogen elements are found in group 7A (or 17) and are known for their reactivity and corrosive nature, while noble gases in group 8A (or 18) are colorless, unreactive gases. The paragraph concludes with a discussion of metalloids, which have properties intermediate between metals and nonmetals, and are found along the zigzag line that divides metals from nonmetals on the periodic table.

Keywords

💡Periodic Table

The Periodic Table is a tabular arrangement of chemical elements organized on the basis of their atomic number, electron configurations, and chemical properties. In the video, the periodic table serves as the central theme, with elements being classified into groups and periods, providing a framework for understanding their properties and behaviors.

💡Groups

Groups, also known as families, are the vertical columns of the periodic table. Each group contains elements that have similar chemical properties due to having the same number of valence electrons. The video explains how groups are numbered and how elements within the same group, such as alkali metals, exhibit similar reactivity.

💡Periods

Periods are the horizontal rows of the periodic table. They represent the electron shells or energy levels that electrons occupy. The video describes periods as a way to categorize elements based on their atomic structure, with elements in the same period having the same number of electron shells.

💡Alkali Metals

Alkali metals are a group of chemical elements from Group 1 (or Group 1A) that include lithium, sodium, and potassium. The video highlights their soft, silvery appearance and extreme reactivity. Alkali metals are never found in their pure state in nature due to their tendency to react with other elements.

💡Hydrogen

Hydrogen is a unique element placed in Group 1 but is not an alkali metal; it is a nonmetal. The video points out that despite being in the same group as alkali metals, hydrogen does not share all their properties, illustrating the complexity of classifying elements.

💡Alkaline Earth Metals

Alkaline earth metals are found in Group 2 (or Group 2A) and include elements like magnesium, calcium, and strontium. The video describes them as being less reactive than alkali metals but still not found in their pure state in nature, highlighting their similar chemical properties.

💡Metals

Metals are a broad category of elements characterized by their malleability, ductility, and conductivity. The video discusses how metals are typically found on the left side of the periodic table and have properties such as being solid at room temperature (except for mercury), good conductors of heat and electricity, and generally not found in their pure state in nature.

💡Nonmetals

Nonmetals are elements that are typically brittle when solid, poor conductors of heat and electricity, and can be found in various states of matter. The video contrasts nonmetals with metals and places them on the right side of the periodic table, with examples including carbon, nitrogen, and oxygen.

💡Halogens

Halogens are a group of nonmetals found in Group 7A (or Group 17), including elements like fluorine, chlorine, and bromine. The video describes them as very reactive, often colorful and corrosive, and known as 'salt formers' due to their tendency to form salts.

💡Noble Gases

Noble gases are found in Group 8A (or Group 18) and include helium, neon, argon, krypton, and others. The video characterizes them as colorless gases that are generally unreactive due to their full valence electron shells, which make them stable and less likely to engage in chemical reactions.

💡Metalloids

Metalloids are elements that have properties intermediate between metals and nonmetals. They are found along the zigzag line that divides metals from nonmetals on the periodic table. The video mentions elements like silicon, germanium, and arsenic as examples of metalloids, with silicon being particularly notable for its use as a semiconductor.

Highlights

The periodic table organizes elements into groups based on their properties.

Groups are the vertical columns on the periodic table, numbered from 1 to 18.

An alternative group numbering system uses A (e.g., 1A, 2A) and skips 3-12.

Valence electrons are a key concept when considering group numbering.

Periods are horizontal rows on the periodic table, with elements like hydrogen and helium in the first period.

Alkali metals, found in group 1 or 1A, include lithium, sodium, and potassium.

Alkali metals are soft, silvery, and highly reactive, not found in pure form in nature.

Elements within the same group exhibit similar chemical properties.

Hydrogen, despite being in group 1, is a nonmetal and behaves differently from alkali metals.

Alkaline earth metals, in group 2 or 2A, include magnesium, calcium, and strontium.

Alkaline earth metals are less reactive than alkali metals but still not found in pure form in nature.

Metals are generally solid at room temperature, malleable, ductile, and good conductors of heat and electricity.

Nonmetals are often brittle, poor conductors of heat and electricity, and can be found in different states of matter.

Halogens, found in group 7A or 17, are very reactive nonmetals known for their corrosive nature.

Noble gases, in group 8A or 18, are colorless, unreactive gases.

Metals are typically found on the left side of the periodic table, while nonmetals are on the right.

The dividing line between metals and nonmetals is a zigzag line, with metalloids having properties between the two.

Metalloids, such as silicon, have properties intermediate between metals and nonmetals and are sometimes semiconductors.

The periodic table's organization helps predict the properties and behaviors of elements based on their groups and periods.

Transcripts

In this video, we're going to look at the periodic table.

We're going to classify the elements into groups.

And so as we go through these terms,

I'm going to be checking them off.

The groups are the vertical columns on the periodic table.

And so, if I go over here, I can see that all of these elements

are in the same vertical column.

So all these elements are in the same group.

And we call this group 1.

I can see that all of these elements

are also in the same column.

So all these elements are in the same group,

and we call this group 2.

I can continue labeling my groups.

This would be group 3, 4, 5, 6, 7, 8, 9, 10, 11, 12.

And then I go back up to here, and I

can see I have another vertical column, so group 13, 14, 15,

16, 17, and finally 18.

So that's one way to number your groups.

There is another way to number your groups,

and that would be to say that group 1 is group 1A,

group 2 is group 2A.

And then kind of ignoring groups 3 through 12,

continue on with your numbering system.

So 1A, 2A-- that would make this group 3A, group 4A,

group five 5A, group 6A, 7A, and finally 8A.

And this second way of numbering your groups

is useful when you're thinking about valence electrons.

And so let's move on to the concept of periods.

A period is a horizontal row on the periodic table.

And so, if I look at period 1, and I just

move across my periodic table, hydrogen is in the first period

and so is helium.

I move on to the second period, so lithium, beryllium, boron,

carbon, nitrogen, oxygen, fluorine, and neon.

And so I can continue with numbering my periods,

so this would be period 3, 4, 5, and 6.

Now notice I don't have the entire periodic table

on this video.

I didn't have enough room, and we're not really

going to talk about all of those elements anyway.

So let's go ahead and focus on metals next.

Let's talk about the alkali metals.

When I'm talking about metals, I'm

going to try to write it in red here.

The alkali metals are found in group 1, or group 1A,

so things like lithium, and sodium, potassium.

So here are my alkali metals.

The alkali metals are soft, silvery metals

that are extremely reactive.

And one nice thing about organizing elements into groups

is elements in the same group have similar chemical

properties.

And so the alkali metals react in similar ways.

For example, all the alkali metals will react with water.

And the alkali metals turn out to be so reactive

that you're not going to find them

in their pure state in nature.

You're not going to walk outside and find

some sodium lying on the ground.

They're found in nature in combination

with other elements.

Let's talk about hydrogen, because hydrogen is also

in group 1, but hydrogen is not an alkali metal.

Hydrogen is a nonmetal.

So let me go ahead and draw that in green here.

I will represent nonmetals in green.

Hydrogen is the exception in group 1.

Next, let's talk about the alkaline earth metals.

You find those in group 2, or group 2A, so right in here.

Things like magnesium and calcium and strontium

are your alkaline earth metals.

Your alkaline earth metals are reactive-- not

quite as reactive as the metals in group 1,

but you don't find these in the pure state, either.

You find them in combination with other elements.

And so once again, the alkaline earth metals

are going to react in similar ways.

They have similar chemical properties,

and so that's, again, a convenient way

of organizing the periodic table into groups.

For right now, let's just go ahead

and say-- groups 3 through 12-- these are all metals in here.

And let's just talk about metals in general for a minute.

Metals, the properties of metals.

Metals are solids at room temperature,

except for mercury.

So here is mercury down here, which is a liquid at room

temperature.

Metals are very malleable, which means

you can form them into different shapes.

They're very workable.

They're not brittle.

Metals are also ductile, which means

you can draw them into wires.

You can form them into wires.

For example, like copper.

Here's copper right here.

Copper wires, of course, carry current in homes.

So metals are good conductors of heat and electricity.

And so those are the properties of metals

that most textbooks will talk about.

Let's contrast those with nonmetals.

Nonmetals-- if you have a solid nonmetal,

those solids would tend to be brittle, not malleable

like metals.

Nonmetals are poor conductors of heat and electricity.

So you find nonmetals in different states of matter.

Let's talk about one of the nonmetals now,

and that would be the halogens.

Let's find the halogens on our periodic table.

You find them in group 7A, or group 17,

things like fluorine, chlorine, bromine.

Here are your halogens right in here.

Halogens are very reactive nonmetals.

So they're often very colorful, very, very corrosive,

and the name halogen actually means salt former.

We're actually going to come back to that in the next video

when we look at some electron configurations

and we talk about why these things are so reactive.

And so those are the halogens.

Next, let's find the noble gases.

The noble gases are found in group 8A, or group 18.

Some of these are very famous, like helium, neon, argon,

krypton.

Here are your noble gases.

They're colorless gases, and they're generally

very unreactive.

Once again, we'll talk about why in the next video

when we talk about some electron configurations.

There are some other nonmetals on here,

which I will identify in a minute.

But first I want to talk about the fact

that you pretty much find metals on the left side

of the periodic table.

So let me go back to the red color.

And you can see I have all these metals over here

on the left side.

And then for my nonmetals, in green, you're

going to find those over here on the right side

of your periodic table.

The dividing line between those--

let me go ahead and draw it in there--

it's kind of a zigzag line.

Let me see if I can sketch it in here.

The dividing line would go something like this.

We're going to go a zigzag line down our periodic table.

And some of the elements that you find on this zigzag line

have properties in between those of metals and nonmetals,

and we call those metalloids.

Let's go ahead and talk about metalloids now.

Metalloids-- oid, of course, being like a metal,

so it's similar to metals, but, again, the properties

are in between those of a metal and a nonmetal.

Some of the elements that are considered to be metalloids

would be boron-- right in here-- silicon, germanium, arsenic,

antimony, tellurium, and sometimes you'll

see astatine listed as one.

It depends on which textbook that you're looking in.

So you can see that some of the elements along this zigzag line

are considered to be metalloids.

And there's no official, one definition for which elements

are considered to be metalloids, and so you

might see a little bit of a discrepancy

there for some of these elements.

But in general, those are the ones

that are considered to be metalloids, silicon probably

being the most famous one.

Silicon is a semiconductor.

It's a metalloid, so it's like a metal,

so it does conduct electricity, but not

to the same extent that a metal would.

And so these intermediate properties

are sometimes useful.

Let's go ahead and mark some of the rest of these.

These would be some other metals.

And then over here on the right would

be the rest of your nonmetals here.

Carbon is nonmetal, nitrogen is nonmetal,

oxygen is nonmetal, phosphorus, sulfur.

So that's just a quick way to divide the periodic table up

with some simple definitions.

In the next video, we'll talk more

about the electronic structure, and we'll

get into definition of transition metals.