Electrons, Bonding and Structure Flashcards
s-orbitals
- spherical shape
- each shell contains one s-orbital
- 2s electrons in each shell
p-orbitals
- 3d dumb-bell shape
- Each shell contains 3 p-orbitals
- 6p electrons in each shells (from n=2 upwards)
d-orbitals
From n=3 upwards each shell contains 5 d-orbitals (10 electrons)
Why do the two electrons in an orbital not repel each other?
An electron has a property called a spin. The two electrons in an orbital must have opposite spins.
The number of electrons in the first 4 shells
1st shell - 2
2nd shell - 8
3rd shell - 18
4th shell - 32
What is an orbital?
A region of space where electrons can be found. It is a region around the nucleus that can hold up to two electrons with opposite spins.
What is a sub-shell?
A group of the same type of orbitals within a shell. An s subshell can hold up to 2 electrons, a p subshell can hold up to 6 and a d up to 10.
What is ionic bonding?
An ionic bond is the electrostatic attraction between oppositely charged ions. Electrons are transferred from a metal to a non-metal.
Giant ionic lattices
Each ion is surrounded by oppositely charged ions and the ions attract each other to form a giant ionic lattice.
Properties of ionic compounds
- High melting and boiling points - large amount of energy required to break strong electrostatic bonds that hold oppositely charged ions together in a solid lattice
- Conduct electricity when molten - ions are free to move
- Solubility - dissolves in polar substances
Why is the melting point of MgO higher than NaCl?
The charges on Mg2+ and O2- are greater than those on Na+ and Cl-. The stronger the charge, the stronger the electrostatic forces between the ions so more energy is required to break.
Why can giant ionic lattice only conduct when molten?`
In a solid lattice, the ions are in fixed positions and can’t move so it can’t conduct electricity. When it is melted, the ions can move to conduct electricity.
How does a polar substance dissolve ionic compounds?
The polar molecules surround the ionic lattice to form a solution. The slight charges within the polar substance are attracted to the charged ions in the giant ionic lattice. This disrupts the lattice and ions are pulled out of it.
What is a covalent bond?
- Occurs between 2 non metals
- electrons are shared between atoms and are attracted to the nuclei of both bonded atoms
Single covalent bonding
When atoms are bonded by one shared pair of electrons. Covalent bonds act in one direction only (unlike ionic bonds)
What are lone pairs?
an outer shell pair of electrons that is not involved in chemical bonding
What is a dative covalent bond?
When one of the atoms supplies both the shared electrons to the covalent bond
Simple molecular structures
- atoms within each molecule are held together by strong covalent bonds
- different molecules are held together by weak intermolecular forces (London forces)
Properties of simple molecular structures
- Low melting and boiling points - little energy required to break London forces between molecules
- Do not conduct electricity as there are no charged particles free to move
- Generally soluble in non polar solvents as London forces can form between these solvents and covalent molecules
Properties of giant covalent structures
- High melting and boiling points as lots of energy required to break strong covalent bonds within lattice
- Non conductors except for graphite where delocalised electrons are able to move freely between layers
- Insoluble in polar and non polar solvents because coavalent bonds in the lattice are too strong
What is the name of the shape of a molecule with 1 bonded electron pairs around the central atom?
Linear
Hydrogen
What is the name of the shape and bond angle of a molecule with 2 bonded electron pairs around the central atom?
Linear
180
Carbon dioxide
What is the name of the shape and bond angle of a molecule with 3 bonded electron pairs around the central atom?
Trigonal planar
120
BF3
What is the name of the shape and bond angle of a molecule with 4 bonded electron pairs around the central atom?
Tetrahedral
109.5
Alkanes
What is the name of the shape and bond angle of a molecule with 5 bonded electron pairs around the central atom?
Trigonal bipyramid
90 and 120
PCl5
What is the name of the shape and bond angle of a molecule with 6 bonded electron pairs around the central atom?
Octahedral
90
SF6
Why does the presence of lone pairs change the shape and how does it change the bond angle?
A lone pair is more electron dense so repels more than a boned pair.
Reduces bond angle by about 2.5 degrees
What is the shape and bond angle of ammonia?
Pyramidal
107
What is the shape and bond angle of water?
Non linear
104.5
What is electronegativity?
Electronegativity measures the atttraction of a bonded atom for the pair of electrons in a covalent bond.
What are permanent dipole-induced dipole interactions?
A molecule with a permanent dipole will have a slight positive end and a slight negative end. When it is near non polar molecules it can cause the electrons in its shells to shift slightly as they are repelled by the negative end or attracted to the positive end. This causes the non polar molecule to become slightly polar and an attraction occurs. This molecule with a permanent dipole has induced a dipole on the other molecule.
What are permanent dipole-permanent dipole interactions?
Molecules with permanent dipoles will be attracted to other molecules with permanent dipoles. The slight positive end of one molecule is attracted to the slight negative end of the other molecule.
What are London forces?
London forces occur between non polar molecules. They are caused by the constant random movement of electrons in atoms’ shells. This movement unbalances the distribution of charge. At any moment there may be an instantaneous dipole across the molecule. This instantaneous dipole will induce a dipole in neighbouring molecules. This causes a weak intermolecular force called a London force or an instantaneous dipole-induced dipole force. The more electrons, the greater the number of attractive forces between molecules.
