what is a Polar Covalent Bond — Reading Comprehension

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"This middle school science passage, aligned with NGSS standards, explores the concept of polar covalent bonds. It explains how these bonds form due to the unequal sharing of electrons between atoms with different electronegativity. The passage uses the example of water (H2O) to illustrate how this unequal sharing creates a dipole, with one end of the molecule having a partial positive charge and the other a partial negative charge. Students will learn the significance of electronegativity in determining bond polarity and understand the real-world implications of these bonds, such as water’s unique properties. The text is designed for self-study and includes a clear, factual tone to aid comprehension of fundamental chemistry principles."

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2D diagram of a water molecule showing the oxygen atom with a partial negative charge and the two hydrogen atoms with partial positive charges, with the shared electrons closer to the oxygen, representing a polar covalent bond. — The polar covalent bonds in a water molecule, where electrons are pulled closer to the more electronegative oxygen atom, creating partial charges.

Chemical bonds are the forces that hold atoms together to form molecules. A covalent bond is a fundamental type of chemical bond where atoms share pairs of electrons. However, this sharing is not always equal. A polar covalent bond occurs when the shared electrons are pulled closer to one atom than the other, leading to an uneven distribution of charge. This happens because some atoms have a stronger attraction for electrons, a property known as electronegativity.

In a polar covalent bond, the atom with higher electronegativity will pull the shared electrons closer to itself. This gives that atom a slight negative charge, represented by the Greek letter delta negative (δ−). The other atom, which has lost some of its electron density, gains a slight positive charge, represented by delta positive (δ+). This separation of charge creates a dipole, a molecule with a positive end and a negative end, similar to the poles of a magnet.

Water (H2O) is a classic example of a molecule with polar covalent bonds. The oxygen atom has a much higher electronegativity than the hydrogen atoms. As a result, the shared electrons are pulled closer to the oxygen atom, giving it a partial negative charge. The hydrogen atoms, in turn, acquire a partial positive charge. This polarity is a key reason why water is an excellent solvent, able to dissolve many substances by surrounding their charged particles. This unique property of water is essential for life on Earth.

Fun Fact: The polarity of water molecules is why water forms a meniscus in a glass tube and why some insects can walk on the surface of water.

What is a key characteristic of a covalent bond?

Atoms transfer electrons.Atoms share electron pairs.Atoms gain a full positive charge.Atoms become completely neutral.

What is the main cause of a polar covalent bond?

Atoms having equal electronegativity.The atoms are of the same element.An unequal sharing of electrons.The molecule is linear in shape.

What is electronegativity?

The number of protons in an atom.The ability of an atom to attract electrons.The total mass of an atom.The number of neutrons in an atom.

In a polar covalent bond, what happens to the atom with higher electronegativity?

It becomes completely positive.It gains a partial positive charge.It becomes completely negative.It gains a partial negative charge.

Which of the following is a real-world example of a molecule with polar covalent bonds mentioned in the passage?

Table salt (NaCl)Hydrogen gas (H2)Carbon dioxide (CO2)Water (H2O)

Based on the passage, what term describes a molecule with a positive end and a negative end?

An isotopeA dipoleA cationAn anion

What is the main idea of the passage?

To explain the concept of electronegativity.To describe why some covalent bonds are polar.To list different types of chemical bonds.To show the importance of water as a solvent.

If an unknown molecule has a polar covalent bond, how would its shared electrons likely be distributed?

Evenly between both atoms.Closer to the more electronegative atom.Closer to the less electronegative atom.Outside of both atoms.