Water and Solutions Review

What is the electron configuration of oxygen?

• 1s² 2s² 2p⁴

• 1s² 2s² 3p⁴

Answer explanation

The electron configuration of oxygen (atomic number 8) is 1s² 2s² 2p⁴. This indicates it has 2 electrons in the 1s subshell, 2 in the 2s subshell, and 4 in the 2p subshell, making the first choice correct.

How many valence electrons does oxygen have?

• 6

• 8

Answer explanation

Oxygen has 6 valence electrons, which are found in its outer shell. This is because it is in group 16 of the periodic table, where elements typically have 6 valence electrons.

Draw the Lewis dot structure of oxygen.

• [Two O atoms with 6 valence electrons each, sharing two pairs of electrons]

• [Two O atoms with 8 valence electrons each, sharing one pair of electrons]

Answer explanation

Oxygen has 6 valence electrons. In the correct structure, two O atoms share two pairs of electrons, forming a double bond, resulting in each atom having a complete octet (8 electrons). Thus, the first choice is correct.

What is the name of the shape of a water molecule?

• Linear

• Bent

Answer explanation

The shape of a water molecule is described as 'bent' due to the angle between the hydrogen atoms, which is approximately 104.5 degrees. This bent shape is a result of the molecule's polar nature and the repulsion between lone pairs of electrons.

What physical properties does water have due to its “bent-ness?”

• High boiling point and surface tension

• Low boiling point and no surface tension

Answer explanation

Water's bent molecular shape leads to strong hydrogen bonding, resulting in a high boiling point and significant surface tension. These properties are crucial for various biological and environmental processes.

Define polarity.

• Distribution of electrical charge over atoms joined by chemical bonds.

• Absence of electrical charge in molecules.

Answer explanation

Polarity refers to the distribution of electrical charge over atoms in a molecule. The correct choice highlights that this distribution occurs in atoms joined by chemical bonds, which is essential for understanding molecular interactions.

Draw a diagram of a polar water molecule and identify its polar ends.

• [Diagram with δ+ on hydrogen and δ- on oxygen]

• [Diagram with δ+ on oxygen and δ- on hydrogen]

Answer explanation

A water molecule is polar due to its bent shape and the difference in electronegativity between oxygen and hydrogen. Oxygen carries a partial negative charge (δ-) while hydrogen carries a partial positive charge (δ+). Thus, the correct diagram shows δ+ on hydrogen and δ- on oxygen.

What is hydrogen bonding? Draw a model of a hydrogen bond between 2 water molecules.

• [Diagram showing hydrogen bonds between hydrogen of one water molecule and oxygen of another]

• [Diagram showing hydrogen bonds between oxygen atoms]

Answer explanation

Hydrogen bonding occurs when a hydrogen atom covalently bonded to an electronegative atom (like oxygen) interacts with another electronegative atom. The correct diagram shows hydrogen bonds between the hydrogen of one water molecule and the oxygen of another.

Why is water described as the “Universal Solvent?”

• It can dissolve many substances due to its polarity.

• It dissolves only a few substances due to its non-polarity.

Answer explanation

Water is called the "Universal Solvent" because its polar nature allows it to dissolve a wide variety of substances, making it effective in many chemical reactions and biological processes.

What is water really good at dissolving?

• Polar substances and ions

• Non-polar substances

Answer explanation

Water is a polar solvent, meaning it effectively dissolves polar substances and ions due to its ability to form hydrogen bonds. Non-polar substances do not dissolve well in water, making the first choice correct.