Atomic Structure and Bonding Flashcards
Charge on an electron
Negative
Charge on a nucleus
Positive
Systems behave in such a way as to…
…reduce stored energy.
Electrostatic forces in an atom
Like charges repel. Electrons have negative charges. They experience repulsion from each other.
Unlike charges attract. Electrons experience attraction towards nuclei.
Electrons have magnetic fields.
If we try to push two electrons together, they will tend to align anti-parallel.
No two electrons can occupy the same state.
This means two electrons cannot both be in the same “place” with the same energy and with the same spin states all at the same time.
Electrons are quantum objects
It is far more useful for us to know the energy of electrons, so we sacrifice our accurate knowledge of electron location and deal with “clouds” of probability, the shape of which tells us where we expect to find an electron if we measured position. We call these “orbitals”.
Ground state
Lowest energy state for an atom.
Orbitals
Each orbital can contain no electrons, one electron or two electrons.
Core Charge
the charge on the atom or ion in the absence of all outer shell electrons. Also known as effective nuclear charge, this gives an indication of the attraction that valence electrons have towards the nucleus
Atomic Radius
the distance from the nucleus to the outermost electrons, measured as half the distance of a single covalent bond between two identical atoms
Electronegativity
a measure of the strength of the attraction between atoms of that element and electrons participating in bonding.
Electron Shielding
the repulsive force exerted by inner shell electrons on outer shell electrons, pushing them away from the nucleus
Molecule
Smallest unit of a simple covalent substance that retains the chemical and physical properties of that substance.
Defined formula that describes the number of atoms in that particle. Atoms positioned in a defined arrangement.
Covalent bond
Strong electrostatic force of attraction between two atomic nuclei and a shared pair of electrons between those atoms.
Electrons in covalent bonds and lone pairs are localized
they are held in place attracted to positive charges on either side. They cannot drift off.
Covalent bonds are directional
they are in a well-defined place.
Electron geometry
We can work this out from the fact that each group of electrons will repel from all the other groups of electrons around the same atom in a molecule.
Molecular geometry
We can work this out from the electron geometry and the types of groups of electrons.
Intramolecular
Bonding within molecules- covalent bonds
Intermolecular
Bonding between separate molecules
Dispersion force
At any instant charge distributions are not symmetrical so there will be weak fluctuating “instantaneous” dipoles.
The negative pole will attract a nucleus in another species (thing) so will both cause and attract a positive pole in the other species.
Dipole-Dipole force
Large difference in electronegativity between the atoms on each side of a covalent bond will result a “polar” bond.
An asymmetric shape of a molecule containing polar bonds will give a molecule that has an overall resultant polarity.
The negative pole attracts to positively charged regions of other species, the positive pole attracts to negatively charge regions of other species.
Hydrogen bond
Electrostatic force of attraction between a hydrogen atom which is covalently bonded to a more electronegative atom or group, and another electronegative atom with a lone pair of electrons.
Melting and boiling points of typical giant covalent structures
High. Many strong covalent bonds required a lot of energy to break.
Electrical conductivity of typical giant covalent structures
Low. Electrons are localized. There are no delocalized electrons, so no charges that are free to move.
Hardness of typical giant covalent structures
High. Covalent bonds are strong so require large amount of energy to break. Covalent bonds are directional, electrons are held between specific nuclei so they cannot move easily and be shared with another nucleus.
Melting and boiling points of simple molecular substances
Relatively low. The bonds that are broken are weaker intermolecular bonds, requiring less energy to break.
Electrical conductivity of simple molecular substances
Low. Particles that may be free to move are overall neutral molecules.
Electrical conductivity of graphite
High. There are delocalised electrons that are free to move. These electrons move in the spaces between the layers and are attracted to the positive charges in the hexagonal layers on either side.
Hardness of graphite
Low. Graphite is soft, because the dispersion forces are relatively weak, and the layers can slide over each other.
Cation
Atom or molecule that have lost one or more electrons, resulting in a net positive electrical charge.
Anion
Atom or molecule that have gained one or more electrons, resulting in a net negative electrical charge.
Giant ionic lattice
Oppositely charged ions attract each other to produce one structure whose size is limited only by the number of ions available, in which there is a repeating pattern – a long-range order exists.
Melting and boiling points of ionic compounds
Giant ionic structure typically have high melting and boiling points, because melting or boiling involves breaking many strong ionic bonds and this requires a large amount of energy.
Hardness of ionic compounds
Because ionic bonds are strong, giant ionic lattices are generally hard (they resist indentation). It takes a lot of energy to change shape.
Brittleness of ionic compounds
Enough stress can cause a plane (layer) of ions to shift to cause ions of the same charges to line up. They then repel and cracks grow very quickly and easily – this is what “brittle” means. The lattice shatters.
Electrical conductivity of ionic compounds
In solid form ions are not free to move, so solid ionic compounds are not electrical conductors. In molten liquid form or in solution the ions are free to move, ionic compounds are electrical conductors when molten or in solution.
Alloy
Metallic structure with different types of atoms in the structure to change properties.
Properties of metals
Electrically conductive, typically malleable and ductile, lustrous and sonorous. Typically high melting and boiling points.
Metallic bonding
Strong, non-directional forces of attraction between a “sea” of delocalized electrons and positive core charges.
Metallic structure
Giant metallic lattice.
Displacement reaction
A more reactive element takes the place of a less reactive element in a salt.
metal + dilute acid
metal salt + hydrogen
metal + oxygen
metal oxide
metal + water
metal hydroxide + hydrogen
metal + steam
metal oxide + hydrogen
solute
substance being dissolved
solvent
the primary component of the solution. It does the dissolving
solution
an evenly distributed mixture of atoms, molecules and/or ions including a liquid solvent and one or more solutes.
precipitate
is an insoluble salt formed from two aqueous reagents.
Precipitates have the state symbol (s) for solid.
spectator ion
The ions not involved in the reaction remain in solution and are called spectator ions.
The spectator ions are not included in the ionic equations;
