Electrons, Bonding and Structure Flashcards
How are shells described and how many are there?
Energy levels and 4
How many electrons can each sub-shell hold:
- s =
- p =
- d =
- f =
- s = 2
- p = 6
- d = 10
- f = 14
How many electrons do each shell hold?
2.8.18.32
General formula of how many electrons can fit into each shell:
What’s the order of filling the electric configuration?
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p
What is the big number in electronic configurations?
The principal quantum number
What are the exceptions of the electronic configuration rules?
What are orbitals?
An orbital is a region around the nucleus which can hold up to a maximum of 2 electrons, with opposite spin
What shape is an s-orbital?
Spherical
What shape is a p-orbital?
Dumbbell
Noble gases:
- Group 0 (or 18) of the periodic table
- They exist as individual atoms (monatomic)
- Their outer shells contain 8 electrons (except Helium which contains 2)
- All their electrons are in pairs
- They are very stable and unreactive/inert
Bonding:
- Atoms combine in order to get the same electron arrangement as a noble gas i.e. 8 electrons in their outer shell (this is called the octet rule)
- They do this by sharing or transferring electrons to form chemical bonds
What is a compound?
A compound is a substance formed when 2 or more different elements chemically bond together in a fixed ratio
What is an ionic bond?
An ionic bond is the electrostatic force of attraction between positive and negative ions e.g. NaCl
What is a covalent bond?
A covalent bond is the strong electrostatic force of attraction between a shared pair of electrons and the nuclei of the bonded atoms e.g. CO2
What is metallic bonding?
Metallic bonding is the strong electrostatic force of attraction between positive metal ions and delocalised outer electrons e.g. copper
Ionic bonding of Na and O
Covalent bonding of P and H
Ionic (and covalent) bonding of NaOH
Exceptions to the octet rule: electron deficiency
Exceptions to the octet rule: expanding the octet
Which elements cannot expand their octet?
Period 2 elements (e.g. N, O, F) cannot expand their octet because they don’t have an f or d sub-shell, and therefore cannot hold more than 8 electrons in their outer shell
Ionic bonds:
- Usually between metals and non-metals
- Electrons are transferred from the metal atom to the non-metal atom
- Oppositely charged ions are formed, which are bonded together by strong electrostatic forces of attraction
- The metal forms a positive ion
- The non-metal forms a negative ion
Structure of ionic compounds:
- 3D giant ionic lattice structure
- Each ion is surrounded by ions of opposite charge
- The ions attract each other strongly in all directions
Melting and boiling points of ionic compounds:
- Ionic compounds are solid at room temperature
- They have high melting and polling points
- This is because it takes a lot of heat energy to overcome the strong electrostatic forces of attraction between the oppositely charged ions in the giant lattice
- The higher the charge on the ions, the stronger the electrostatic forces of attraction between the oppositely charged ions, and so more heat energy is required to break the bonds
Electrical conductivity of ionic compounds:
- Ionic compounds do not conduct electricity as solids, but do conduct when molten or dissolved in water
- In a solid, the ions are in fixed positions in the ionic lattice and so cannot move
- When melted or dissolved in water the ions are free to move and carry charge
Solubility of ionic compounds:
Ionic compounds are soluble in polar solvents (e.g. water)
What is a dative covalent bond?
A dative covalent bond (or co-ordinate bond) is a shared pair of electrons where both of the electrons have been provided by only one of the bonding atoms
How are dative covalent bonds displayed?
- A dative covalent bond can be written as A —>B
- The direction of the arrow shoes the direction in which the electron pair has been donated
Ammonium ions:
Oxonium ions (H3O+)
- When an acid is added to water, the water molecules form oxonium ions, H3O+
- H3O+ ions are responsible for reactions of acids, In equations, the oxonium ion is often simplified as H+ (aq)
- In the oxonium ion, one of the lone pairs around the oxygen atom in an H2O molecule provides both the bonding electrons to form a dative covalent bond
What are the types of covalent structures?
- A simple molecular lattice
- A giant covalent lattice
What is a molecule?
A molecule is a small group of atoms held together by covalent bonds
What is electronegativity?
Electronegativity is the ability of an atom to attract the bonding electrons in a covalent bond
Average bond enthalpy:
Not all covalent bonds are the same strength. Some are much stronger than others, which means that more energy would be required to break them, for example during a reaction. A measure of the average energy of a bond (and therefore the energy that would be needed to break it) is called the average bond enthalpy
Electron pair repulsion theory
- The shape of a molecule is determined by the number of electron pairs in the outer shell of the central atom
- These electron pairs repel each other and arrange themselves as far apart as possible
- A lone pair causes more repulsion than a bond pair
- In general, a lone pair reduces the bond angle by ≈ 2.5°
lp-lp repulsion > lp-bp repulsion > bp-bp repulsion
What are the most electronegative atoms?
Non-polar bonds:
Polar bonds:
Polar molecules:
- Non-polar molecules are symmetrical
- This means that the dipoles act in different directions and cancel each other out - leaving no overall dipole
To figure out if a molecule is polar, you can see if it would fit in a ‘magnetic field’. If yes, then the molecule is polar, if not, then the molecule is non-polar
Intermolecular forces:
Permanent dipole-dipole interactions:
Hydrogen bonding:
London forces:
Melting and boiling points of simple molecular structures:
Electrical conductivity of simple molecules structures:
Solubility of simple molecular structures:
Anomalous properties of water:
Shape of a molecule with 2 bond pairs around the central atom:
Shape of a molecule with 3 bond pairs around the central atom:
Shape of a molecule with 4 bond pairs around the central atom:
Shape of a molecule with 5 bond pairs around the central atom:
Shape of a molecule with 6 bond pairs around the central atom:
Shape of a molecule with 3 bond pairs and 1 lone pair around the central atom:
Shape of a molecule with 2 bond pairs and 2 lone pairs around the central atom:
Shapes of molecules when there is a double bond:
Shapes of molecules when there is no central atom:
What are the giant covalent structures?
- Diamond
- Graphite
- Silicon dioxide
- Graphene
- Silicon
- Boron
- Carbon
Diamond:
- A giant covalent, 3D tetrahedral lattice structure
- Each carbon atom is bonded to 4 others - meaning that diamond has very strong covalent bonds
- It has a very high melting point
- It doesn’t conduct electricity
- It is insoluble
- Silicon dioxide has a similar structure
Graphite:
- Graphite is made up of layers of carbons in hexagonal rings, where each carbon atom is bonded to 3 others
- It is a giant covalent lattice
- There is a sea of delocalised electrons between these layers
- Graphite can conduct electricity as it’s delocalised electrons are free to move and carry charge
- Graphite has a high melting and boiling point due to its strong covalent bonds
- Graphite is insoluble
Graphene:
- Graphene forms a 2-dimensional giant lattice of interlocking hexagonal rings of carbon, 1 atom thick (a single layer)
- This means that graphene is very strong, whilst very light, and therefore has many versatile uses (e.g. in nanotechnology)
- Graphene can conduct electricity
