Electrons, bonding and structure Flashcards
How many electrons are there in each of the first 4 electron shells when full?
1st shell: 2 electrons
2nd shell: 8 electrons
3rd shell: 18 electrons
4th shell: 32 electrons
What is an orbital?
The region of space in which an electron orbits the nucleus in an atom.
How many electrons can each orbital hold?
2
What shape does an s orbital have?
A spherical shape
What shape does a p orbital have?
A dumbbell shape, like a figure of eight.
At any one energy level it is possible to have up to ______ absolutely equivalent p orbitals pointing mutually at right angles to each other
3
What is the Aufbau principle? (the order of filling of orbitals) and Hund’s rule?
Electrons fill low energy orbitals first and progress. For orbitals with the same energy, the electrons fill singly first before the second electrons are added to orbitals.
What is the point of Hund’s rule?
It helps to minimise the repulsions between electrons, therefore making the atom more stable
Why does 4s fill before 3d?
3d has a slightly higher energy level than 4s
How many orbitals are there in s, p, d and f?
s: 1
p: 3
d: 5
f: 7
Define ionic bonding
Electrostatic attraction between positively and negatively charged ions.
Why is NaCl referred to as 6:6 coordinated?
Each chloride ion is touching 6 sodium ions and vice versa, which is the maximum number of ions that can fit around a sodium ion. This gives the ionic compound energetic stability. If more ions are introduced, chloride ions will start touching each other, causing repulsion.
Why do ionic compounds have high melting and boiling points?
The electrostatic forces of attraction between oppositely charged ions is strong, so a lot of heat energy is required to overcome them.
Why is the mp and bp of MgO higher than that of NaCl?
Mg and O have charges of 2+ and 2- respectively, which have stronger electrostatic forces of attraction than the 1+ and 1- charges on Na and Cl.
How does the size of ions affect mp and bp?
Smaller ions have stronger electrostatic forces of attraction as they can be closer together, and so have higher mp and bp
Why are ionic compounds often brittle?
If layers of an ionic compound shift slightly, ions of the same charge are brought next to each other and repel each other, causing the compound to break apart.
Why are many ionic compounds soluble in water?
Positive ions are attracted to the lone pairs on water molecules, and if this attraction outweighs that to the negative ions in the ionic compound, dative (coordinate) covalent bonds can form between the positive ions and water. Water molecules form hydrogen bonds with the negative ions.
Why are ionic compounds often insoluble in organic solvents?
The attractions between the ions and the solvent molecules are not strong enough to outweigh the ionic bonds.
Why don’t ionic compounds conduct electricity when solid?
The ionic compounds have no free ions or delocalised electrons in their giant ionic lattice, so there are no mobile ions to carry charge.
Why do molten ionic compounds conduct electricity?
In a liquid state, the ions are mobile and therefore free to move and carry charge through the compound
What is a covalent bond?
The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.
What is a dative covalent bond?
A covalent bond in which both electrons in the shared pair of electrons are derived from the same atom
What is average bond enthalpy?
The average enthalpy change when one mole of gaseous bonds are broken
Define bond dissociation enthalpy
The enthalpy required to break one mole of bonds to give separate atoms.
2bonding pairs 0lone pairs
Linear, 180º
3bonding pairs, 0lone pairs
Trigonal planar, 120º
4bonding pairs, 0lone pairs
Tetrahedral, 109.5
5bonding pairs, 0lone pairs
Trigonal bipyramidal, 90º and 120º
6bonding pairs, 0lone pairs
Octahedral, 90º
2bonding pairs, 1lone pair
Bent/ Non-linear, less than 120º
3bonding pairs, 1lone pair
Trigonal Pyramidal, 107º
4bonding pairs, 1lone pair
See-saw, 90º and 120º
5bonding pairs, 1lone pair
Square Pyramidal, 90º and 180º
2bonding pairs, 2lone pairs
Bent, 104º
3bonding pairs, 2lone pairs
T-shaped, 90º and 120º
4bonding pairs, 2lone pairs
Square Planar, 90º and 180º
What is VSEPR?
Valence Shell Electron Pair Repulsion: The valence electron pairs surrounding an atom tend to repel each other, so they adopt an arrangement that minimises the repulsion.
Define electronegativity
The ability of an atom to attract the bonding pair of electrons in a covalent bond.
What makes a polar molecule polar?
The molecule must contain a polar bond- a covalent bond in which there’s a difference in electronegativity between the two atoms and therefore one atom is slightly positive and the other negative. The molecule must not be symmetrical in its charge or else the charges cancel each other out.
What are van der Waal’s forces?
Temporary intermolecular forces caused by shifts in electron density in an atom which cause temporary dipoles that result in induced dipoles in nearby atoms.
What affects van der Waal’s force strength?
Molecular mass. Greater molecular mass gives stronger VDW forces as there are more electrons.
Why are hydrogen bonds the strongest intermolecular force?
There’s a large difference in electronegativity between oxygen and hydrogen, (which makes water very polar) and this gives a very strong permanent dipole interaction.
Why is ice less dense than water?
The molecules in ice are held apart by hydrogen bonds and ice has an open lattice structure.
Why is the melting point of ice relatively high?
The hydrogen bonds are strong, so more energy is required to break them.
Why does water have a cohesive property?
Cohesiveness is a result of the hydrogen bonds
Why is water a good solvent?
The polarity of water molecules makes them a good solvent as solutes can interact with the charged regions. Water can form hydrogen bonds with solutes.
Why does water have a relatively high specific heat capacity?
The hydrogen bonds make water relatively stable
Define a dipole
A dipole is a difference in charge between the two atoms caused by a shift in electron density in the bond. The greater the difference in electronegativity, the more polar the bond.
Why are the covalent bonds in diatomic gases non polar?
The two atoms have equal electronegativity and so the electrons are equally attracted to both nuclei.
What makes a bond purely covalent?
To be purely covalent, a bond must be between two atoms of the same element, such as in diatomic gases. This is because there is 0 difference in electronegativity between the two.
How do induced dipole-dipole forces form?
Electrons in charge clouds are constantly moving. At any particular moment the electrons are likely to be more to one side than the other, which gives the atom a temporary dipole.
This dipole causes other temporary dipoles in neighbouring atoms, which attracts the atoms to each other. This begins a domino effect of induced dipoles. As the electrons are constantly moving, the dipoles are created and destroyed all the time, but the overall effect is attraction.
What gives molecules stronger induced dipole-dipole forces?
Larger molecules will have larger electron clouds and this gives stronger induced dipole forces. Molecules with larger surface areas have a more exposed electron cloud and so their induced dipole forces are stronger.
What are permanent dipole-dipole interactions?
Where the delta+ and delta- charges on polar molecules cause weak electrostatic forces of attraction between molecules.
What are the three elements that hydrogen can covalently bond to?
Oxygen, nitrogen or fluorine.
How do you melt or boil a simple covalent compound in terms of the bonds?
To melt or boil a simple covalent compound you do not have to break the covalent bonds, it is the intermolecular forces that hold molecules together that must be overcome. This is why simple covalent molecules have relatively low melting and boiling points.
