Bonding Flashcards
What is an ionic bond?
An ionic bond is the electrostatic attraction between positively and negatively charged ions.
How do you determine the formula of an ionic compound?
The total positive charge must balance the total negative charge. The charges on individual ions determine how many of each ion is needed.
What is the formula for caesium oxide?
Cs₂O. Caesium (Cs⁺) has a +1 charge, and oxygen (O²⁻) has a -2 charge. Two Cs⁺ ions are needed to balance the charge.
What is the formula for ammonium sulfate?
(NH₄)₂SO₄. Ammonium (NH₄⁺) has a +1 charge, and sulfate (SO₄²⁻) has a -2 charge. Two NH₄⁺ ions are needed to balance the charge.
Why do ionic compounds have high melting points?
Strong electrostatic forces between oppositely charged ions require large amounts of energy to overcome.
Do ionic compounds conduct electricity?
Only when molten or dissolved in water, as ions must be free to move.
What is a covalent bond?
A covalent bond is a shared pair of electrons between two atoms.
How is a covalent bond formed?
The positively charged nuclei of both atoms attract the shared electrons.
Why do covalent molecules not conduct electricity?
They have no overall charge and do not contain free-moving charged particles.
What is a dative covalent bond?
A covalent bond where both electrons in the shared pair come from one atom.
What type of bond is found in carbon monoxide (CO)?
A triple bond consisting of two normal covalent bonds and one dative covalent bond.
What is metallic bonding?
The attraction between positive metal ions and a sea of delocalised electrons.
How does metallic bonding explain metal properties?
- High melting points: Strong attraction between metal ions and delocalised electrons.
- Conductivity: Delocalised electrons move freely, carrying charge
Why does magnesium have a higher melting point than sodium?
- Magnesium has a higher charge density (+2 vs. +1 for sodium).
- Magnesium’s atomic radius is smaller, so electrons are more strongly attracted to the nucleus.
What are the four main types of crystal structures?
Ionic, metallic, macromolecular (giant covalent), and molecular.
What are the structure of the four main types of crystal structures?
Ionic Crystals
• Lattice of positive and negative ions (e.g., NaCl).
• High melting points due to strong electrostatic forces.
• Conduct electricity when molten or dissolved but not when solid.
Metallic Crystals
• Metal ions surrounded by a sea of delocalised electrons.
• High melting points and electrical conductivity.
Macromolecular (Giant Covalent) Crystals
• Atoms held by covalent bonds in a giant lattice (e.g., diamond, graphite).
• High melting points due to strong covalent bonds.
• Diamond is hard and does not conduct electricity.
• Graphite conducts electricity due to delocalised electrons.
Molecular Crystals
• Held together by weak intermolecular forces (e.g., iodine, ice).
• Low melting points because intermolecular forces are weak.
• Do not conduct electricity (no free-moving charged particles).
Why is diamond so hard?
Each carbon atom forms four strong covalent bonds in a tetrahedral structure.
Why does diamond have a high melting point?
Large amounts of energy are needed to break its strong covalent bonds.
Why does graphite conduct electricity while diamond does not?
Graphite has delocalised electrons that can move between layers, whereas diamond has none.
What forces hold graphite layers together?
Van der Waals forces.
What are intermolecular forces?
Forces between molecules, not within them.
Why does carbon dioxide exist as a gas at room temperature?
Weak intermolecular forces do not require much energy to break.
What are van der Waals forces?
Weak attractions between molecules due to temporary dipoles.
What are hydrogen bonds?
Stronger intermolecular forces that form between molecules with H attached to N, O, or F (e.g., water).
Why does ice have a crystalline structure?
Hydrogen bonds hold water molecules in a fixed pattern
What determines the shape of a molecule?
The number of bonding and lone electron pairs around the central atom.
How do electron pairs affect molecular shape?
- Bonding pairs and lone pairs repel each other.
- Lone pairs repel more strongly than bonding pairs.
What are some common molecular shapes and bond angles?
Methane
Ammonia
Water
What is the order of increasing electron pair repulsion?
• Order of increasing electron pair repulsion:
1. Bonding pair–Bonding pair (weakest repulsion)
2. Lone pair–Bonding pair (moderate repulsion)
3. Lone pair–Lone pair (strongest repulsion)
Why does water (H₂O) have a bond angle of 104.5°?
The two lone pairs on oxygen exert stronger repulsion on the bonding pairs, reducing the bond angle from 109.5° (tetrahedral) to 104.5°.
What are the five steps to predicting molecular shape?
- Determine the number of electron pairs (bonding & lone pairs).
- Identify the basic shape (e.g., tetrahedral, trigonal planar).
- Check for lone pairs.
- Apply repulsion rules to adjust bond angles.
- Draw the final shape with accurate bond angles.
What is the shape and bond angle of the ammonium ion (NH₄⁺)?
• Shape: Tetrahedral
• Bond angle: 109.5°
• No lone pairs affect the shape.
What is the molecular shape of hydrogen sulfide (H₂S)?
Bent
Why does H₂S have a bond angle of 104.5° instead of 109.5°?
The two lone pairs on sulfur exert stronger repulsion on bonding pairs, reducing the bond angle.
What is electronegativity?
The ability of an atom to attract bonding electrons in a covalent bond.
How does electronegativity change across the periodic table?
• Increases across a period (due to higher nuclear charge and smaller atomic radius).
• Decreases down a group (due to increased shielding and atomic size).
Why is the H-F bond in hydrogen fluoride (HF) polar?
Fluorine is more electronegative than hydrogen, pulling electron density toward itself, creating a polar bond (Hδ⁺—Fδ⁻).
Which element is the most electronegative?
Fluorine (4.0 on the Pauling scale).
Which elements are the least electronegative?
Caesium and Francium (0.8 on the Pauling scale).
What two factors determine an atom’s electronegativity?
- Atomic radius – Smaller atoms attract bonding electrons more strongly.
- Nuclear charge – More protons mean a stronger attraction to electrons.
What is the difference between polar bonds and polar molecules?
• Polar bonds occur when atoms have different electronegativities (e.g., HCl).
• A polar molecule has an overall dipole moment (e.g., H₂O).
Why is tetrachloromethane (CCl₄) non-polar despite having polar bonds?
The molecule is symmetrical, so the dipoles cancel out, making it non-polar.
What are the three types of intermolecular forces?
- Permanent dipole–Permanent dipole (e.g., HCl).
- Permanent dipole–Induced dipole (e.g., Cl₂ near HCl).
- Induced dipole–Induced dipole (Van der Waals/London forces) – Weakest (e.g., CH₄).
What factors affect Van der Waals forces?
- Molecular size – Larger molecules have stronger Van der Waals forces.
- Surface area – Longer, unbranched molecules have stronger forces.
Why does pentane (C₅H₁₂) have a higher boiling point than ethane (C₂H₆)?
Pentane molecules are larger, allowing more Van der Waals forces to form.
What is hydrogen bonding?
A strong intermolecular force occurring when hydrogen is bonded to highly electronegative atoms (N, O, F).
Why is hydrogen bonding stronger than dipole-dipole interactions?
Hydrogen has no inner non-bonding electrons, so the nucleus (proton) is strongly attracted to lone pairs on N, O, or F.
How does hydrogen bonding affect water’s properties?
• Higher boiling/melting points than expected.
• Ice is less dense than liquid water due to an open lattice structure
What is the general trend in boiling points of hydrides down Groups 16 and 17?
Boiling points increase due to increasing molecular size.
Why do water (H₂O) and hydrogen fluoride (HF) have unusually high boiling points?
Hydrogen bonding increases the energy needed to separate molecules
What is the chemical formula of ethanoic acid?
CH₃COOH
How does hydrogen bonding affect ethanoic acid’s physical properties?
It increases its melting and boiling points compared to molecules of similar size.
