Bonding and Structure Flashcards
Covalent bond definition
A bond formed by a shared pair of electrons
Ionic bonding definition
An electrostatic attraction between oppositely-charged ions
Dative covalent bond definition
A shared pair of electrons which has been provided by one of the bonding atoms only
What is the shape of a simple molecule determined by?
Repulsion between electron pairs surrounding a central atom
Give the shape and bond angle of a molecule with 2 bonding pairs of electrons and no lone pairs
Linear
180
Give the shape and bond angle of a molecule with 3 bonding pairs of electrons and no lone pairs
Trigonal planar
120
Give the shape and bond angle of a molecule with 4 bonding pairs of electrons and no lone pairs
Tetrahedral
109.5
Give the shape and bond angle of a molecule with 3 bonding pairs of electrons and 1 lone pair
Triangular pyramidal
107
Give the shape and bond angle of a molecule with 2 bonding pairs of electrons and 2 lone pairs
V-shaped
104.5
Give the shape and bond angle of a molecule with 6 bonding pairs of electrons and no lone pairs
Octahedral
90
Electronegativity definition
The ability of an atom to attract the bonding electrons in a covalent bond
How may a permanent dipole arise?
A permanent dipole is something with a δ+ and a δ- at all times (ie a polar bond)
They occur when covalently-bonded atoms have different electronegativities
What are the 4 most electronegative elements?
Fluorine, oxygen, nitrogen, chlorine
These elements can form polar bonds
What intermolecular force do all molecules have?
Van der Waals’
These are the only forces that act between non-polar molecules
What groups must a molecule contain to form hydrogen bonds?
OH or NH
How do hydrogen bonds arise?
The O-H or N-H bond is polar because of the difference in negativity between hydrogen and oxygen
If 2 molecules were approach each other, the δ+ end of one molecules would be attracted to the δ- end of the other molecule
One of the lone pairs of electrons from one molecule can form a partial dative covalent bond with the δ+ H on the other molecule
How do Van der Waals’ forces arise?
Electrons in molecules are constantly moving. At any instant, the distribution may not be symmetrical. This results in an instantaneous temporary dipole. This dipole induces dipoles in neighbouring molecules and leads to an attraction between the opposite charges in the dipoles. These attractions between molecules are Van der Waals’
Describe and explain the 2 factors affecting the strength of Van der Waals’ forces
The more electrons there are in the molecule, the greater the fluctuations in the electron cloud, and the stronger the Van der Waals’ forces
The greater the contact area between molecules, the stronger the induced dipoles that develop. Long, thin molecules can line up beside each other more closely than short, spherical ones. So unbranched molecules have stronger Van der Waals’ forces than branched molecules
Describe and explain the anomalous properties of water
Relatively high boiling point - hydrogen bonds and Van der Waals’ forces must be broken, which requires more energy than just overcoming Van der Waals’
More dense than ice - ice has an open lattice with hydrogen bonds holding the water molecules apart. When ice melts, the hydrogen bonds collapse, allowing water molecules to move closer together
Metallic bonding definition
The attraction of positive ions to delocalised electrons
Describe and explain the structure of a giant metallic lattice
A giant metallic lattice consists of a regular array of positive ions surrounded by a sea of delocalised electrons. The metal is held together by the attraction between positive ions and delocalised electrons
Describe and explain the properties of a giant metallic lattice
High melting and boiling point - there is a very strong attraction between the positive ions and the delocalised electrons, and a lot of energy is required to break the bonds
Conduct electricity - the delocalised electrons are free to move around and carry charge throughout the structure
Malleable & ductile - the layers of atoms can slide over each other
Explain how alloys affect the structure of a metal
Alloying a metal involves introducing atoms of different sizes into the structure, which disrupts the regularity of the layers. This means the layers cannot slide over each other as easily, and are therefore harder
Describe the structure of a giant ionic lattice
Each ion is surrounded by oppositely charged ions, which attract each other to form a giant ionic lattice
