Atoms and the Periodic Table

Atoms and the Periodic Table

Middle School

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Learning Objectives

• Define atoms and their parts: protons, neutrons, and electrons.

• Use the periodic table to find an element's atomic number, symbol, and mass.

• Calculate the number of protons, neutrons, and electrons in an atom.

• Differentiate between metals, nonmetals, and metalloids by their properties.

• Describe how models show how electrons are arranged in an atom.

Key Vocabulary

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Atom

An atom is the basic unit of matter, made of protons, neutrons, and electrons.

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Nucleus

The center of the atom, which contains the protons and neutrons, and makes up the atomic mass.

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Atomic Number

This number tells you the number of protons and electrons found in an atom of an element.

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Periodic Table

A chart showing all known chemical elements, organized by atomic number and chemical properties.

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Element

A substance that is composed of a single kind of atom and cannot be broken down further.

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Valence Electrons

These are the electrons that are located in the outermost shell of an atom.

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The Structure of an Atom

• Atoms are the fundamental building blocks of matter that can form molecules.

• The nucleus contains protons (positive charge) and neutrons (no charge).

• Electrons carry a negative charge and orbit the central nucleus.

• An atom's mass is the sum of its protons and its neutrons.

Multiple Choice

Which two particles are found in the nucleus of an atom and contribute to its atomic mass?

• Electrons and protons

• Only protons

• Protons and neutrons

• Neutrons and electrons

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What Is the Periodic Table?

• It’s a chart organizing elements by atomic number and electron configuration.

• ​Elements are grouped by recurring chemical properties in columns called groups.

• The table’s seven rows are called periods; metals are on the left.

• Nonmetals are generally found on the right side of each period.

Multiple Choice

What do elements in the same group on the periodic table have in common?

• They are all nonmetals

• They are in the same period

• Similar chemical behaviors

• The same number of protons

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Reading an Element's Box on the Periodic Table

• Each element's box provides key information about its properties and structure.

• The atomic number equals the number of protons and electrons in the atom.

• The element symbol is a one or two-letter shorthand for the element’s name.

• Mass number is the sum of protons and neutrons in the nucleus.

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Multiple Choice

An element's atomic number tells you the number of:

• Protons and electrons

• Only neutrons

• Protons and neutrons

• Neutrons and electrons

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Calculating Protons, Neutrons, and Electrons

APE

• ​The mnemonic APE stands for Atomic Number = Protons = Electrons.

• ​​An element's atomic number is always equal to the number of protons in its nucleus.

• ​For a neutral atom, the number of electrons is the same as the number of protons.

MAN

• ​The mnemonic MAN stands for Mass Number – Atomic Number = Neutrons.

• ​​To find the number of neutrons, subtract the atomic number from the mass number.

• ​The mass number is found by rounding the atomic weight to the nearest whole number.

Multiple Choice

An atom has an atomic number of 7 and an atomic weight of 14. How many neutrons does it have?

• 14

• 21

• 0

• 7

Metals, Nonmetals, and Metalloids

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Metals

• ​Found on the left and middle of the periodic table.

• ​​They are typically shiny, malleable, and can be stretched into wires.

• ​They are excellent conductors of both heat and also electricity.

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Nonmetals

• ​Found on the right side of the periodic table.

• ​​They are generally dull in appearance and are very brittle.

• ​They are poor conductors of both heat and also electricity.

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Metalloids

• ​Located in a staircase pattern between metals and nonmetals.

• ​​They have a unique mix of properties from both groups.

• ​Silicon is a semiconductor used in many electronic devices.

Multiple Choice

An element is a brittle solid that is a poor conductor of electricity. How would it be classified?

• Nonmetal

• Noble Gas

• Metal

• Metalloid

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Electron Models and Valence Electrons

Bohr Model

• This model shows an atom with electrons in specific orbits, also known as shells, around the nucleus.

• The first shell can hold 2 electrons, the second shell holds 8, and the third holds up to 18.

• The electrons located in the outermost shell of an atom are called the valence electrons.

Lewis Dot Model

• This is a simplified way to show how reactive an atom is by representing its valence electrons.

• It uses the element's chemical symbol, with dots around it showing the number of valence electrons.

• The fullness of this outer valence shell determines how the atom will interact with other atoms.

Multiple Choice

Which part of an atom determines its reactivity and is represented by dots in a Lewis Dot Model?

• Valence electrons

• Electrons in the first shell

• Protons in the nucleus

• The total number of neutrons

Elements, Compounds, and Mixtures

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Element

• ​A pure substance that is made up of only one kind of atom.

• ​​It cannot be broken down into simpler substances by chemical or physical means.

• ​Examples of elements are Hydrogen and Oxygen, which are basic building blocks.

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Compound

• ​A substance formed when two or more elements are chemically bonded together.

• ​​Its properties are very different from its original constituent elements.

• ​A common example of a compound is pure water which is H₂O.

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Mixture

• ​A combination of substances that are physically mixed but not chemically bonded.

• ​​Each substance in a mixture retains its own original chemical identity.

• ​An example of a mixture would be mixing sand with sugar.

Multiple Choice

What is the key difference between a compound and a mixture?

• A compound can be separated by physical means, while a mixture cannot.

• A mixture has components that are all the same element, while a compound does not.

• A compound involves a chemical bond, while a mixture does not.

• A mixture is a pure substance, while a compound is not.

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Common Misconceptions About Atoms

Misconception	Correction
Electrons have a positive charge.	Electrons have a negative charge. Protons have a positive charge.
An element is made of multiple types of atoms.	An element is a pure substance made from only one type of atom.
Atomic mass is just the number of protons.	Atomic mass is the sum of protons and neutrons in an atom.

Multiple Choice

How do the properties of metals and nonmetals differ regarding their physical state and conductivity?

• Both metals and nonmetals are excellent conductors of heat.

• Metals are poor conductors of electricity, while nonmetals are good conductors.

• Metals are shiny and conduct electricity, while nonmetals are dull and are poor conductors.

• Metals are dull and brittle, while nonmetals are shiny and malleable.

Multiple Choice

Which statement is correct for a neutral atom?

• Atomic number equals the number of neutrons.

• Number of electrons equals the number of protons.

• Atomic number equals the total number of protons and neutrons.

• Electrons are always more than protons.

Multiple Choice

If an atom has 10 electrons, how are they arranged in shells according to this model?

• 2 in the first shell, 8 in the second shell

• 2 in the first shell, 2 in the second shell, 6 in the third shell

• 8 in the first shell, 2 in the second shell

• 2 in the first shell, 8 in the third shell

Multiple Choice

You discover a new element that is a brittle solid but also a semiconductor of electricity. How would you justify its classification on the periodic table?

• As a metalloid, because it has properties intermediate between metals and nonmetals.

• As a nonmetal, because it is brittle.

• As a compound, because it has mixed properties.

• As a metal, because all solids that conduct electricity are metals.

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Summary

• Atoms are made of protons, neutrons, and electrons.

• The periodic table organizes elements by atomic number and similar properties.

• Elements are classified as metals, nonmetals, or metalloids based on their properties.

• Matter can be classified as an element, a compound, or a mixture.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

• 1

• 2

• 3

• 4