Lesson Video: The Periodic Table | Nagwa Lesson Video: The Periodic Table | Nagwa

Lesson Video: The Periodic Table Science • Second Year of Preparatory School

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In this video, we will learn how to describe and identify the rows, periods and blocks of the Periodic Table, and the position of different types of element.

16:08

Video Transcript

In this video, we will learn how to describe and identify the rows, periods, and blocks of the periodic table and the position of different types of elements. We’ll examine how the modern periodic table is arranged and relate the position of an element on the periodic table to its electronic configuration.

Elements are substances that consist of one type of atom. There are 118 known elements that each have their own unique set of properties. These elements have been arranged to create the modern periodic table of elements, where each box of the periodic table represents a different element. Of these elements, 92 occur naturally on Earth in significant amounts. The rest, like curium and einsteinium, are typically artificially created and only exist in the laboratory setting, sometimes only for a very short amount of time.

The elements neptunium and plutonium do occur naturally in small amounts. But their discovery was through artificial production. The element technetium is also often considered an artificially made element. While technetium does exist naturally, most of it has decayed away. So, nowadays, it is typically artificially created.

Most of the elements are solids at room temperature. Most of these elements, like iron, sodium, and gold, have a high melting and boiling point. Only two elements, bromine and mercury, are liquids at room temperature. And the rest are gases at room temperature, as these elements have very low melting and boiling points. The low boiling point of nitrogen makes liquid nitrogen useful in medicine to preserve tissues such as the cornea of the eye.

It’s worth mentioning that not much is known about the elements shown here in pink. Because they have only been artificially synthesized in very small quantities. We might expect them to be solids or gases as shown. However, some scientists disagree about how these elements will behave.

The elements of the periodic table can take on several forms, where some of these forms are stable and others are unstable. The unstable forms are radioactive and give off radiation in the form of high-energy rays or particles. All elements have an unstable radioactive form, though typically the most stable form of an element is the most common found in nature.

The elements boxed in pink do not have a stable form and are always radioactive. The radiation produced by a radioactive element may be harmful. But in many instances, the radioactive element can be used in a positive way. For example, cobalt-60, an unstable form of the element cobalt, is used in food preservation. Cobalt-60 produces 𝛾-rays, which prevent the reproduction of microbial cells without impacting human health.

Elements can exhibit other interesting properties. For example, silicon is a semiconductor. This means it can conduct electricity differently depending on the temperature, which makes silicon useful for creating computer chips.

Now that we’ve learned about some of the properties of the elements, let’s take a closer look at the periodic table and how it’s arranged.

Each of the boxes or cells of the periodic table contains information about the element. This cell shows some of the most common information that is typically represented. The chemical symbol is usually written in the middle of the box. This symbol consists of a single capital letter or a capital letter followed by a lowercase letter.

The name of the element often appears below the chemical symbol. The atomic mass typically appears at the bottom of the cell. The atomic mass of the elements varies widely, with hydrogen having an atomic mass of one and lead having an atomic mass of 207. Above the chemical symbol is the atomic number. This number is unique for each element. The atomic number indicates the number of protons in the nucleus of an atom of that element. Hydrogen has an atomic number of one. So an atom of hydrogen has a single proton in its nucleus. Carbon has an atomic number of six. So an atom of carbon has six protons in its nucleus.

Atomic number is one of the properties used to organize the elements in the modern periodic table. In the modern periodic table, the elements are organized in order of increasing atomic number from left to right. But the periodic table isn’t just a long list of elements. The elements are organized into precise rows and columns.

A column on the periodic table is known as a group. There are 18 groups that are usually numbered sequentially from left to right. We may also encounter an older numbering system for groups, shown here in pink. A row on the periodic table is called a period. There are seven periods numbered from top to bottom. The elements are organized into these groups and periods according to their electronic configurations. To better understand this organization, let’s take a look at the electronic configurations of the first 18 elements.

As we look at the electronic configurations, we can see that atoms of elements in the same group tend to have the same number of valence electrons or electrons in the outermost energy level. In addition, the A grouping numbers indicate how many valence electrons atoms of elements in the group will have. So atoms of elements in group one A have one valence electron. And atoms of elements in group six A will have six valence electrons.

The atoms of elements in the last column all have full outer shells or energy levels. Atoms of these elements all have eight valence electrons, except for helium, which only has two. Because elements in the same group have similar electronic configurations, these elements also have similar chemical properties and reactivity. For example, the elements in group seven A are highly reactive and can react with metals to form metal salts, while the elements in group zero, with full valence shells, are stable and unreactive.

If we look at the electronic configurations across a period, we see that atoms of elements in the same period have the same number of occupied energy levels. The number of occupied energy levels corresponds to the period number. In addition, atoms of elements in the same period have the same outermost energy level. The outermost energy level in atoms of elements found in period one is K. The outermost energy level in period two is L. And the outermost energy level in period three is M.

We can now use the periodic table to determine how many valence electrons an atom has, how many energy levels the electrons occupy, and which energy level is the outermost energy level. But the periodic table can provide us with even more information. The periodic table can be further divided to indicate which sublevel the valence electrons are found in. The sublevels are called s, p, d, and f.

With all of this information in mind, let’s consider the element phosphorus. Phosphorus is in period three. So the electrons in an atom of phosphorus will occupy three energy levels, with the outermost energy level being energy level M. Phosphorus is found in group five A. This means that an atom of phosphorus will have five electrons in its outermost energy level. This also means that the innermost energy levels will be full, with two electrons in the K energy level and eight electrons in the L energy level.

Furthermore, as phosphorus is in the p block, some of its valence electrons will be found in the p sublevel. In addition to being divided into s, p, d, and f blocks, the periodic table can also be divided into specifically named groups and sections. The elements in group one, excluding hydrogen, are known as the alkali metals. The elements in group two are called the alkaline earth metals. The elements in group 18 are called the inert gases. And the elements in group 17, or seven A, are called the halogens.

The elements found in the middle section of the periodic table are called the transition metals. The two rows that are separated from the main portion of the periodic table each have their own name that comes from the names of the first element in each row. The top row is called the lanthanides after the element lanthanum, and the bottom row is called the actinides after the element actinium.

The organization of the periodic table reveals several patterns or trends in the properties of the elements. One of these trends is atomic radius. Atomic radius describes the size of an atom. It is typically measured in picometers. A picometer is very small. One picometer is equivalent to 10 to the negative 12 meters. In general, atomic radius tends to increase down a group and from right to left across a period. So elements with a small atomic radius are found on the top right of the periodic table. And elements with a large atomic radius are found on the bottom left.

We can explain this trend by looking at the electronic configurations of elements in the same group and same period. Hydrogen, lithium, and sodium are all found in group one of the periodic table. We can see that an atom of each of these elements has one more occupied energy level than the element above it. The more occupied energy levels an atom has, the larger the atomic radius, as the occupied higher energy levels are further from the nucleus.

Now let’s look at an atom of lithium, carbon, and neon, three elements found in the same period. Atoms of these elements have the same number of energy levels. So, to understand which atom has a larger atomic radius, we need to look at the nucleus. An atom of lithium has three protons in its nucleus, an atom of carbon has six protons, and an atom of neon has 10 protons. As the number of protons in the nucleus increases, the attraction between the nucleus and the outer electrons increases. The outer electrons will be pulled closer to the nucleus when the attraction is stronger, making the atomic radius smaller. So an atom of neon will be smaller than an atom of carbon, which is smaller than an atom of lithium.

Another periodic trend involves the metallic character of an element. Metallic character relates to the tendency to lose electrons. The majority of the elements on the periodic table are metals. Metals have a strong metallic character. This means that during a chemical reaction, atoms of these elements tend to lose electrons and form positive ions. The nonmetallic elements have a weak metallic character. Atoms of these elements do not tend to lose electrons easily. During chemical reactions, atoms of nonmetals often share electrons or gain electrons to form negative ions. The metalloid elements can be considered to have a metallic character between the metals and the nonmetals.

Lastly, we have the inert gases, which are stable, unreactive, and do not tend to lose electrons or form ions. In general, we can see that metallic character increases as we move down a group and from right to left across a period. This is similar to the trend for atomic radius. In fact, an increase in atomic radius tends to correspond to an increase in metallic character. This is because as the atomic radius increases, the electrons are less attracted to the nucleus, which means that they can be lost more easily.

We’ve learned a lot about the organization of the periodic table in this video. But before we summarize what we’ve learned, let’s take a look at a question.

How many electrons in the outermost level will an element in the fourth period and one A group in the periodic table have?

The periodic table is a way to represent and organize the 118 known elements. Each horizontal row of the periodic table is called a period. There are seven periods numbered from top to bottom. The period number indicates the number of occupied energy levels in an atom of that element. The element in the question is found in the fourth period. So an atom of this element has four occupied energy levels.

Each vertical column in the periodic table is called a group. There are 18 groups numbered from left to right. The groups can also be numbered using an A-B numbering system. For the A groups, the group number indicates the number of electrons in the outermost energy level. The element in the question is found in group one A. So an atom of this element has one electron in the outermost energy level. This element happens to be potassium. So the number of outermost electrons in an atom of potassium, which is found in period four and group one A of the periodic table, is one.

Now let’s review what we’ve learned with the key points. The periodic table of elements is used to organize the 118 known elements that each have a unique set of chemical and physical properties. Each cell of the periodic table provides information about the element, including chemical symbol, element name, atomic number, and atomic mass. Each of the 18 columns are called groups, and each of the seven rows are called periods.

Atomic number increases from left to right across a period. Atoms of elements found in the same group have the same number of outermost electrons. The period number is equal to the number of occupied energy levels in an atom. The periodic table can be broken down into different sections, including sublevels and named groups. The organization of the periodic table reveals various trends. The atomic radius and the metallic character of an element increase moving down a group and from right to left across a period.

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