Structure and Bonding Flashcards
Ionic Bonding
- An electrostatic attraction between 2 oppositely charged ions
- Happens between metals and non-metals
Properties of Ionic Compounds
- Always solid at room temperature
- Conduct electricity when molten or dissolved as ions are free to move and carry charge
- High melting and pointing points as lots of energy is needed to break strong electrostatic forces of attraction between the ions
- Brittle and shatter easily when the layers of alternating charge are distorted in a lattice. The charges repel causing the lattice to fragment
Covalent Bonding
- Electrostatic attraction between the nucleus of an atom and a shared pair of electrons
- Happens between non-metals
Double Bond
- When the atoms each share 2 electrons with each other
- E.g. Carbon Dioxide
Triple Bond
- When the atoms each share 3 electrons with each other
- E.g. Carbon Monoxide
Properties of Simple Molecular Compounds
- Low melting and boiling points due to weak Van Der Waals forces
- Don’t conduct electricity because there are no particles that can carry charge
Dative Covalent Bond/Coordinate Bond
- A bond where both electrons in the shared paired are supplied by the same atom
- Represented using an arrow
- Once a dative bond has formed, it is treated as a standard covalent bond as it reacts in the same way as one
Examples of Dative Covalent Bonds
- NH3 and H+ become NH4+
- A double bond between carbon and oxygen becomes a triple bond (oxygen shares an extra lone pair so carbon also has a full outer shell)
Metallic Bonding
- A lattice of positively charged ions surrounded by a sea of delocalised electrons
- Strong electrostatic forces of attraction between the oppositely charged ions
- Occurs between metals
Properties of Metallic Structures
- Good conductors of electricity/heat
- Malleable
- Ductile
- High melting and boiling points
Explanation of Metallic Structure Properties
- Good conductors of electricity/heat as they have delocalised electrons that can carry charge through the structure
- Malleable and ductile as the layers of positive ions are able to slide over one another
- High melting/boiling points due to strong electrostatic forces of attraction which require lots of energy to break
Electronegativity
- The tendency of an atom to attract a bonding pair of electrons in a covalent bond
Factors impacting Electronegativity
- Atomic Radius
- Distance from nucleus
- Nuclear Charge
- Electron Shielding
How does Atomic Radius impact Electronegativity?
A smaller atom has a higher electronegativity as the pair of electrons is closer do the nucleus so there is less shielding
How does Nuclear Charge impact Electronegativity?
Increased nuclear charge increases electronegativity as the more protons there are, the stronger the attraction to the shared pair of electrons
What is the trend in electronegativity along a period and why?
- Electronegativity increases because the nuclear charge increases but the shielding stays the same
- There is a greater attraction to the shared pair of electrons so there is a higher electronegativity
What is the trend in electronegativity down a group and why?
- Electronegativity decreases but shielding increases
- Shared pairs of electrons are less attracted to the nucleus so electronegativity decreases
How does a bond become polar?
When there is a clear difference in electronegativity of the atoms involved in a covalent bond
What 2 things does a molecule need to be a polar molecule
- Contain polar bonds
- Not be symmetrical in terms of polar bonds
What causes symmetry in molecules?
- When the bonds are all the same (e.g. AlCl3)
- In symmetrical molecules, the polar bonds cancel each other out
What type of molecule has intermolecular forces?
Covalent compounds with a single molecular structure
Types of Intermolecular Forces
- Permanent dipole forces
- Hydrogen Bonding
- Induced dipole-dipole forces (AKA Van Der Waals forces)
- Ion induced dipole forces
Van Der Waals Forces
- Weakest type of intermolecular force
- All simple covalent molecules have Van Der Waals forces
- All atoms and molecules have positive and negative charges even though they are neutral overall
- These charges produce very weak electrostatic forces of attraction between all atoms and molecules
Permanent Dipole Forces
- Occurs between polar molecules when there is a difference in electronegativity between atoms
- The more electronegative atom will attract the bonding pair of electrons and this creates an electronegative region and an electropositive region
- The electronegative region of one atom will be attracted to the electropositive region of another atom
- This creates a lattice structure as many molecules are held together
Linear
- 2 bonding pairs
- 0 lone pairs
- Bond angle: 180 degrees
Trigonal Planar
- 3 bonding pairs
- 0 lone pairs
- Bond Angle: 120
Tetrahedral
- 4 bonding pairs
- 0 lone pairs
- Bond Angle: 109.5
Trigonal Pyramidal
- 4 bonding pairs
- 1 lone pair
- Bond Angle: 107
Bent
- 4 bonding pairs
- 2 lone pairs
- Bond Angle: 104.5
Trigonal Bipyramidal
- 5 bonding pairs
- 0 lone pairs
- Bond Angles: 120 and 90
Seesaw
- 5 bonding pairs
- 1 lone pair
- Bond Angles: 102 and 86.5
T-Shape
- 5 bonding pairs
- 2 lone pairs
- Bond Angle: 87.5
Linear (5 pairs)
- 5 bonding
