2.4 Structure and Bonding Flashcards
Electron pair geometry
How regions of electron density arrange themselves around a central atom
Trigonal pyramid
A molecular geometry with four regions of electron density and one lone pair
Tetrahedron
A molecular geometry with four regions of electron density and no lone pairs
V-shaped (bond angle of 109.5°)
A molecular geometry with four regions of electron density and two lone pairs
V-shaped (bond angle of 120°)
A molecular geometry with three regions of electron density and one lone pair
Trigonal planar
A molecular geometry with three regions of electron density and no lone pairs
What is VSEPR theory?
Valence Shell Electron Pair Repulsion theory states that regions of electron density will arrange themselves as far apart from each other as possible, so as to minimise the repulsion felt between them
Electronegativity
A measure of an atom’s TENDENCY to attract bonding electrons to itself
Why do the elements in group 18 have no electronegativity?
The elements in group 18 all have full valence shells. They do not need to bond to gain or lose electrons, so they do not attract bonding electrons to themselves
Dipole
The separation of positive and negative charges (a polar bond creates a dipole)
Covalent bond
The bond between two atoms that forms when a pair of electrons is shared between them
Brittle
A property of a substance that describes how a substance will snap/ shatter when a force is applied
Delocalised electrons
Electrons that are not assigned to one specific atom, but are free to move around the structure
Ductility
The ability of a substance to be stretched into wires when a force is applied
Endothermic reactions
Chemical reactions involving a transfer/ ABSORPTION of energy from the surroundings into the system
Exothermic reactions
Chemical reactions involving a transfer/ RELEASE of energy from the system into the surroundings
Intermolecular forces
The attractive forces that occur BETWEEN molecules, holding them together
Intramolecular forces
The attractive forces that occur WITHIN individual molecules, holding the atoms that make up that molecule together
Ionic bond
The electrostatic attraction that occurs between positively charged cations and negatively charged anions
Malleability
A substance’s ability to be bent into different shapes when a force is applied. Can usually be hammered/ rolled into thin sheets.
Metallic bond
The electrostatic attraction between positively charged metal nuclei and the negatively charged delocalised electrons
Soluble
Whether or not a substance can be dissolved in a liquid (the solvent)
System
All the energy and matter (particles/ molecules) involved in a chemical reaction
What are the elements in group 1 called?
Alkali metals
What are the elements in group 2 called?
Alkali earth metals
Radioisotope
An isotope that is unstable and undergoes radioactive decay
What are the elements in groups 3-12 called?
Transition metals
Alloy
A metallic bond that occurs between different metals or with non-metals
What direction are metal bonds?
Metallic bonds are non-directional, as electrons are equally attracted to all the cations in the structure, and can move between them randomly
Electrostatic attraction
The attractive forces between oppositely electrically charged objects
Why are metals insoluble in ANY type of solvent?
The metallic bond between the delocalised electrons and nuclei is too strong to be overcome by the attractive forces between the solvent and the particles within the metal
Why do metals have high electrical conductivity?
Electrical conductivity requires a substance to have free-moving, charged particles in order for it to carry an electrical current. Metals have negatively charged, delocalised electrons that are free to move throughout the metal lattice. When a current is applied to a metal. the delocalised electrons will be attracted to the positive electrode and can move through the metal lattice towards it. Therefore this allows current to flow
Why are metals malleable/ ductile?
The particles in metals can move past each other and remain strongly bonded. When metal nuclei are forced into a new position, they will still experience strong electrostatic bonding with the delocalised electrons around them due to non-directional bonding. So the metal nuclei can slide past each other and settle into a new position once there is no longer a force
Why do most metals have high melting points?
The strong forces of attraction between delocalised electrons and their positive nuclei are difficult to overcome and require a lot of heat energy to do so
Why are metals dense?
The cations are packed tightly together in a rigid lattice
Molecular substances
Substances made up of multiple molecules packed together
Why CAN’T a polar solute dissolve in a non-polar solvent?
The molecules in the solute are unable to interact strongly with the molecules in the solvent. The forces of attraction between the different molecules in much stronger than any potential forces of attraction between the solvent and the solute. They will therefore remain in separate layers.
Why CAN a polar solute dissolve in a polar solvent?
The solute-solute and solvent-solvent forces are of similar strength. This means that the two can interact strongly with each other. The intermolecular forces between the solute molecules will be broken, and the individual molecules will form new intermolecular forces with the solvent molecules.
Polyatomic ions
Charged particles made up of groups of atoms that act as a single unit in an ionic compound
