The Structure of Matter Section 1
Section 1: Compounds and Molecules
Preview
• How Does Structure Affect Properties?
• Water Bonding
The Structure of Matter Section 1
Key Ideas
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What holds a compound together?
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How can the structure of chemical compounds be shown?
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What determines the properties of a compound?
The Structure of Matter Section 1
Chemical Bonds
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What holds a compound together?
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The forces that hold atoms or ions together in a compound are called chemical bonds.
• chemical bond: the attractive force that holds atoms or ions together
The Structure of Matter Section 1
Chemical Structure
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How can the structure of chemical compounds be shown?
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The structure of chemical compounds can be shown by various models. Different models show different aspects of compounds.
• chemical structure: the arrangement of atoms in a substance
The Structure of Matter Section 1
Chemical Structure, continued
• Some models represent bond lengths and angles.
• bond length: the average distance between the nuclei of two bonded atoms
• bond angle: the angle formed by two bonds to the same atom
The Structure of Matter Section 1
Chemical Structure:
Models
Ball-and-Stick Space-filling
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Chemical Structure, continued
• In a ball-and-stick model, atoms are represented by balls. The bonds that hold the atoms together are represented by sticks.
• Space-filling models show the space occupied by atoms.
The Structure of Matter Section 1
Chemical Structure, continued
• Bonds can bend, stretch, and rotate without breaking.
– Bonds can be represented by flexible springs.
– Most reported bond lengths are average distances.
– Bonds hold atoms together tightly.
The Structure of Matter Section 1
How Does Structure Affect Properties?
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What determines the properties of a compound?
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The chemical structure of a compound determines the properties of that compound.
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Properties like melting point, boiling point, color, odor…
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How Does Structure Affect Properties? continued
• Compounds with network structures are strong solids.
_They have high melting point and boiling point.
– Example: Quartz, SiO
2 and oxygen atoms.
is made of silicon
– The atoms are bonded in a strong, rigid structure.
The Structure of Matter Section 1
Water Bonding:
The strength of attractions between molecules varies.
– Attractions between water molecules are called hydrogen bonds.
The Structure of Matter Section 1
Water Bonding
Hydrogen bonds are not as strong as the bonds holding oxygen and hydrogen atoms together within a molecule.
The Structure of Matter Section 1
Choose the correct answer:
1.Which of the following models could be used to compare the space occupied of atoms in a molecule?
a. Ball-and stick b. Structural c. Space- filling d. Formula
The Structure of Matter Section 1
Continue:
2. A hydrogen bond between two water molecules is ______ than the bond inside an individual water molecule?
a. stronger b. the same strength c. Weaker d. None of the above
The Structure of Matter Section 1
Continue:
• 3. Attractions between water molecules are called _______.
a. Hydrogen bonds b. Ionic bonds c. Metallic bonds d. None of the above
The Structure of Matter Section 1
Continue:
• 4. Which of the following models would show the bond angle?
a. Ball- and-stick b. Space-filling c. Structural d. Formula
Section Review p:182 numbers: 1 and 3
