Reading the Periodic Table
Learn how to read the periodic table—find elements by period and group, identify atomic number and symbols, and classify metals, nonmetals, and metalloids by position and properties.
What you'll do in this lesson
A voice-first session with the Crimsora tutor on Reading the Periodic Table, then targeted practice and FRQs — with the tutor adapting to where you get stuck.
What this lesson covers
The periodic table is one of the most powerful tools in science. It organizes all 118 known elements in a way that reveals their properties and helps you predict how they will behave. In this lesson, you will learn to navigate the periodic table like a scientist: finding elements by their position, reading their symbols and atomic numbers, and understanding why elements in the same column act so similarly. These skills are your foundation for understanding chemistry.
The Layout: Periods and Groups
The periodic table is organized into rows and columns, each with a special name and purpose. Rows are called periods, numbered 1 through 7 from top to bottom. Columns are called groups, numbered 1 through 18 from left to right. Each period and group tells you something important about the atoms in it.
The period number tells you how many electron shells (or energy levels) an atom has. An element in period 2, for example, has 2 electron shells. An element in period 5 has 5 shells. This is a quick way to understand the atomic structure without memorizing the arrangement for every single element.
The group number relates to the number of electrons in the outermost shell, which controls how an element will bond and react with others. Elements in the same group have the same number of outermost electrons, which is why they behave so much alike. This repeating pattern of properties across the groups is what makes the periodic table truly periodic.
The period number tells you how many electron shells (or energy levels) an atom has. An element in period 2, for example, has 2 electron shells. An element in period 5 has 5 shells. This is a quick way to understand the atomic structure without memorizing the arrangement for every single element.
The group number relates to the number of electrons in the outermost shell, which controls how an element will bond and react with others. Elements in the same group have the same number of outermost electrons, which is why they behave so much alike. This repeating pattern of properties across the groups is what makes the periodic table truly periodic.
Reading an Element's Card
Every element on the periodic table is shown with several key pieces of information. The most important are the element symbol (a one- or two-letter abbreviation), the atomic number (the number of protons in the nucleus), and usually the atomic mass (the average mass of its isotopes, which you will study in later lessons).
The atomic number is almost always shown as the smallest, boldest number on the card—usually at the top. The symbol is the large letter(s) in the center. The atomic mass sits below, often in smaller print. For example, carbon is shown with the symbol C, atomic number 6, and atomic mass approximately 12. When you need to find an element, always start by locating it in the table using the period (row) and group (column), then read its properties from the card itself.
The position on the table and the atomic number work together: as you move left to right and top to bottom, the atomic number increases. This ordering reflects the increasing number of protons in each nucleus.
The atomic number is almost always shown as the smallest, boldest number on the card—usually at the top. The symbol is the large letter(s) in the center. The atomic mass sits below, often in smaller print. For example, carbon is shown with the symbol C, atomic number 6, and atomic mass approximately 12. When you need to find an element, always start by locating it in the table using the period (row) and group (column), then read its properties from the card itself.
The position on the table and the atomic number work together: as you move left to right and top to bottom, the atomic number increases. This ordering reflects the increasing number of protons in each nucleus.
Metals, Nonmetals, and Metalloids
One of the most important ways to read the periodic table is to recognize where metals, nonmetals, and metalloids are located. A metal is an element that is typically shiny, conducts electricity well, conducts heat well, and can be bent or hammered into different shapes without breaking (it is malleable). A nonmetal is an element that is typically dull, does not conduct electricity, does not conduct heat well, and is brittle—it breaks easily when you try to bend it. A metalloid is an element that has properties between metals and nonmetals—it may look shiny but conducts electricity only under certain conditions.
On the periodic table, metals occupy the left and center regions. Nonmetals are clustered on the right side, especially in groups 14 through 18. Metalloids form a zigzag staircase line that separates metals from nonmetals. You can identify an element's type by remembering this layout, but you can also predict it by understanding how atoms gain, lose, or share electrons. Metals tend to lose electrons, nonmetals tend to gain them, and metalloids do either depending on what they bond with. As you study more, you will see that position and behavior are always connected.
On the periodic table, metals occupy the left and center regions. Nonmetals are clustered on the right side, especially in groups 14 through 18. Metalloids form a zigzag staircase line that separates metals from nonmetals. You can identify an element's type by remembering this layout, but you can also predict it by understanding how atoms gain, lose, or share electrons. Metals tend to lose electrons, nonmetals tend to gain them, and metalloids do either depending on what they bond with. As you study more, you will see that position and behavior are always connected.
Group Behavior: Patterns Across Columns
The real power of the periodic table is that elements in the same group behave alike. This happens because they have the same number of electrons in their outermost shell. For example, all the alkali metals in group 1 (lithium, sodium, potassium, rubidium, cesium) have one electron in their outer shell. They are all soft, shiny metals that react vigorously with water. Sodium reacts so violently that it catches fire. Potassium does too. You do not need to memorize the reactivity of each one individually—the group membership tells you the pattern.
At the opposite end, all the noble gases in group 18 (helium, neon, argon, krypton, xenon, radon) have a full outer shell of electrons. They are extremely unreactive—they barely react with anything. This is why noble gases are used in light bulbs and balloons: they will not burn or react. Again, position predicts behavior. Understanding these group patterns means that once you learn how one element in a group reacts, you can predict the behavior of all its neighbors in that column. This predictive power is what makes the periodic table an organizing principle, not just a reference chart.
At the opposite end, all the noble gases in group 18 (helium, neon, argon, krypton, xenon, radon) have a full outer shell of electrons. They are extremely unreactive—they barely react with anything. This is why noble gases are used in light bulbs and balloons: they will not burn or react. Again, position predicts behavior. Understanding these group patterns means that once you learn how one element in a group reacts, you can predict the behavior of all its neighbors in that column. This predictive power is what makes the periodic table an organizing principle, not just a reference chart.
Why Organization Matters
The periodic table was not invented all at once; it was discovered through observation. In the 1860s, scientists noticed that certain elements had similar properties and tried to arrange them in a way that made sense. A Russian chemist named Dmitri Mendeleev organized the elements by atomic mass and left gaps for elements that had not been discovered yet. When those elements were later found, they fit his predictions perfectly. This proved that the periodic table revealed something real about nature.
Today, we organize by atomic number rather than atomic mass, and we know far more about why the patterns exist. But the lesson remains the same: the periodic table is not random. Every position conveys information. Learning to read it—to find an element, to understand its type, and to predict its behavior from the group it belongs to—gives you the ability to make sense of the chemical world. This skill will help you throughout your chemistry studies.
Today, we organize by atomic number rather than atomic mass, and we know far more about why the patterns exist. But the lesson remains the same: the periodic table is not random. Every position conveys information. Learning to read it—to find an element, to understand its type, and to predict its behavior from the group it belongs to—gives you the ability to make sense of the chemical world. This skill will help you throughout your chemistry studies.
Key terms
- Period.
- A horizontal row on the periodic table; the period number indicates how many electron shells an atom of that element has.
- Group.
- A vertical column on the periodic table; elements in the same group have the same number of outermost electrons and similar chemical properties.
- Atomic number.
- The number of protons in the nucleus of an atom; this defines which element it is and usually appears as the smallest number on an element's card.
- Element symbol.
- A one- or two-letter abbreviation that represents an element (for example, H for hydrogen, Na for sodium).
- Metal.
- An element that is typically shiny, conducts electricity and heat well, and can be bent or shaped without breaking.
- Nonmetal.
- An element that is typically dull, does not conduct electricity well, is brittle, and tends to gain electrons in bonding.
- Metalloid.
- An element with properties between metals and nonmetals; may look shiny but conduct electricity only under certain conditions.
- Noble gas.
- An element in group 18 with a full outer shell of electrons; extremely unreactive and rarely forms bonds.
Worked example
Use the periodic table to find the element phosphorus (P) and answer the following: (a) What is its atomic number? (b) What period is it in? (c) What group is it in? (d) Is it a metal, nonmetal, or metalloid? (e) Name another element in the same group and predict whether it will have similar chemical properties.
Start by locating phosphorus on the periodic table. Look for the symbol P. You will find it on the right side of the table, in the upper-middle region.
(a) Atomic number: Look at the smallest number on phosphorus's card. The atomic number is 15, which means a phosphorus atom has 15 protons.
(b) Period: Count the rows from the top. Phosphorus is in the 3rd row, so it is in period 3. This tells you that a phosphorus atom has 3 electron shells.
(c) Group: Count the columns from the left. Phosphorus is in the 15th column, so it is in group 15 (also called group 5A in older notation). This means it has 5 electrons in its outermost shell.
(d) Metal, nonmetal, or metalloid: Phosphorus sits on the right side of the periodic table, in the region where nonmetals are located. It is indeed a nonmetal. You can predict this from its position: it is far to the right, away from the metals on the left. If you held white phosphorus, it would be dull, brittle, and would not conduct electricity.
(e) Other elements in group 15: Nitrogen (N) is directly above phosphorus in group 15, and arsenic (As) is directly below it. Since they are in the same group, they will have similar chemical properties to phosphorus. All three tend to gain 3 electrons when bonding, and all three are nonmetals. Nitrogen is a gas at room temperature, phosphorus is a solid, and arsenic is a metalloid, but their core chemistry is similar because of their shared group membership.
(a) Atomic number: Look at the smallest number on phosphorus's card. The atomic number is 15, which means a phosphorus atom has 15 protons.
(b) Period: Count the rows from the top. Phosphorus is in the 3rd row, so it is in period 3. This tells you that a phosphorus atom has 3 electron shells.
(c) Group: Count the columns from the left. Phosphorus is in the 15th column, so it is in group 15 (also called group 5A in older notation). This means it has 5 electrons in its outermost shell.
(d) Metal, nonmetal, or metalloid: Phosphorus sits on the right side of the periodic table, in the region where nonmetals are located. It is indeed a nonmetal. You can predict this from its position: it is far to the right, away from the metals on the left. If you held white phosphorus, it would be dull, brittle, and would not conduct electricity.
(e) Other elements in group 15: Nitrogen (N) is directly above phosphorus in group 15, and arsenic (As) is directly below it. Since they are in the same group, they will have similar chemical properties to phosphorus. All three tend to gain 3 electrons when bonding, and all three are nonmetals. Nitrogen is a gas at room temperature, phosphorus is a solid, and arsenic is a metalloid, but their core chemistry is similar because of their shared group membership.
Practice questions
Which of the following statements correctly describes the relationship between an element's position on the periodic table and its properties?
- The atomic number increases as you move from left to right and top to bottom, and elements in the same period always have similar reactivity.
- Elements in the same group have the same number of outermost electrons, which is why they behave similarly; elements in the same period have the same number of electron shells.
- An element's reactivity is determined only by its atomic mass, not by its position on the table.
- Metals are found on the right side of the periodic table, while nonmetals are found on the left side.
Answer: Elements in the same group have the same number of outermost electrons, which is why they behave similarly; elements in the same period have the same number of electron shells.
This statement captures the core organizing principle of the periodic table. Elements in the same vertical column (group) share the same number of electrons in their outermost shell, which controls how they bond and react—that is why they behave alike. Elements in the same horizontal row (period) have the same number of electron shells, which is a different property. The first choice incorrectly suggests that elements in the same period behave similarly (they do not). The third choice ignores the importance of electron structure and position. The fourth choice reverses the correct layout—metals are on the left and center, nonmetals on the right.
Sodium and potassium are both in group 1 of the periodic table. They are both soft, shiny metals. Sodium reacts vigorously with water, releasing heat and catching fire. Without looking up potassium's reactivity, predict how potassium will react with water and explain your reasoning using periodic table principles.
Answer: Potassium will react even more vigorously with water than sodium does. It will likely catch fire and release more heat and energy.
Both elements are in group 1, which means they both have exactly 1 electron in their outermost shell. This electron arrangement is the main factor that controls how readily they react. Potassium is below sodium in the same group—it is in period 4 while sodium is in period 3. Having more electron shells, potassium's outer electron is held less tightly by the nucleus, so it is easier to remove. Therefore, potassium reacts even faster and more violently than sodium. This is an example of how group membership and position work together: the same group tells you the elements will behave alike, and the specific period tells you the relative intensity of that behavior. You can make this prediction without memorizing potassium's properties because you understand the underlying pattern.
FAQ
- How do I find a specific element on the periodic table?
- Use the element's symbol—a one- or two-letter abbreviation. Scan the table systematically, checking each block. Once you locate the symbol, you can read the atomic number (usually the smallest number, often at the top), the atomic mass (usually below the symbol), and the element's position (period and group). If you do not know the symbol, you can search by atomic number if you know it, or learn the symbols of common elements like C (carbon), N (nitrogen), O (oxygen), H (hydrogen), and Na (sodium).
- Why do elements in the same group behave alike if they are not the same element?
- Elements in the same group have the same number of electrons in their outermost shell. The outermost electrons are the ones involved in bonding and chemical reactions. Because all elements in a group have the same outer-shell electron count, they follow the same bonding patterns and react in similar ways. For example, all group 1 elements have 1 outer electron, so they all tend to lose that electron in reactions. The elements are not identical—they have different atomic numbers and different numbers of inner shells—but their chemical behavior is determined by the outer electrons, which is the same across the group.
- How can I tell the difference between a metal, a nonmetal, and a metalloid just by looking at the periodic table?
- Metals occupy the left side and center of the periodic table. Nonmetals are found on the right side, especially in groups 14, 15, 16, 17, and 18. Metalloids form a jagged staircase line that separates the metal region from the nonmetal region—they are the elements that border this line, including boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), and tellurium (Te). If you look at the layout, you can predict the type without memorizing every element. When in doubt, remember the key properties: metals conduct electricity and are malleable, nonmetals do not conduct and are brittle, and metalloids are in between.
- Does the order of elements on the periodic table have a meaning, or is it just random?
- The order is absolutely meaningful. Elements are arranged by increasing atomic number (left to right, top to bottom), which reflects the increasing number of protons. This ordering is not random—it was discovered because scientists noticed that elements with similar properties appeared at regular intervals. The pattern emerges because atoms with the same number of outermost electrons (which repeats in a cycle as you go down the table) have similar chemistry. The periodic table is called periodic because the properties repeat periodically, like notes on a musical scale. Understanding this order helps you predict properties without memorizing every single element.
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The Crimsora tutor teaches Reading the Periodic Table live — explaining on a whiteboard, asking you questions, and adapting to where you get stuck.