Exam 2 Flashcards
Ionic bonding
electrostatic attraction between oppositely charged particles
Lattice energy
energy change required to form a mole of crystalline lattice from a mole of each gaseous ion
What happens as distance between ions increases?
Lattice energy decreases
Covalent bonding
involves the sharing of electrons between 2 non metallic elements
What type of bonding requires an empirical formula?
Covalent bonding
Law of multiple proportions
same elements, but different ratio equals a completely different ratio
refers to covalent bonds
Are covalent compounds molecules?
yes
Are ionic compounds molecules?
no
Lattice
positive and negative ions come together to form ionic compounds in a lattice structure
this structure consists of a positive cation surrounded by negative anions
Properties of the ionic lattice
since there are so many attractive forces, it takes a large amount of energy to break them apart
this gives ionic lattices a high melting point
Properties of covalent bonds
the covalent bonds inside the molecules are very strong
however, the forces attracting neighboring molecules are very weak
Which has a lower melting point molecular bonds or ionic bonds?
Molecular bonds
because of weak force of attraction between molecules
Is lattice energy positive or negative?
It depends on how you define it
If defined as splitting up a lattice into gaseous ions, then it will always be negative since it is an exothermic reaction (energy released)
If defined as a combining of gaseous ions into a lattice, then it will be positive since it is an endothermic reaction (energy required)
Relationship between lattice energy and ionic bond strength
Greater lattice energy = greater ionic bond strength
It takes more energy to break apart ions since there is less distance between them and greater force of attraction
What is lattice energy directly proportional to?
Charge
What is lattice energy indirectly proportional to?
Distance between ions
What happens to potential energy as two same charges get closer together?
Force of attraction decreases
So potential energy increases
What happens to potential energy as two opposite charges get closer together?
Force of attraction increases
So potential energy decreases
Potential energy “calibration” for opposite charges
Goes from more negative to less negative as distance between the electron and nucleus increases
as distance increases (force of attraction decreases), potential energy approaches 0 (increases)
Is force of attraction greater in He+ or H (have the same protons)?
Greater in He+ because helium has more protons than hydrogen pulling at the one electron
Why would Cr have the configuration [Ar] 4s1 3d5?
Having a two paired electrons in the 4s orbital makes electron-electron repulsion increase and thus potential energy goes up
Therefore, want to have no paired electrons because this decreases electron-electron repulsion and thus gives the overall system less energy
Effective nuclear charge
the actual magnitude of the positive charge experienced by an electron
= (# of protons) - core electron shielding
What is the relationship between effective nuclear charge and electron shielding?
As electron shielding increases, effective nuclear charge decreases
Why are orbitals with the same energy level degenerate in hydrogen but not in multi-electron atoms?
Since hydrogen only has 1 electron, there are not other atoms to reduce the effective nuclear charge
For example, 2p is being affected by shielding from 2s so it bumps up to a higher energy level (feels less force of attraction, so has higher energy)
Relationship between effective nuclear charge and atomic radius
As effective nuclear charge increases, atomic radius decreases since there is a stronger force of attraction
What happens to atomic radius as you go down? Explain.
Increases
Since the effective nuclear charge increases, but the core electrons also increase, there is less force of attraction, so the radius increases
Also, n is increasing which indicates bigger size because there are more shells which increases shielding and distance
Why does atomic radius decrease as you go across?
Since protons increase but core electrons (in the same shell) remain the same, there is a net effective nuclear charge increase which pulls electrons closer, thus decreasing the radius
Ionization energy
the amount of energy needed to remove one mole of electrons from one mole of a certain element
Why does it take energy to remove an electron from an atom?
Need to overcome the force of attraction
Also think, you are moving to n = ∞, so need to absorb energy to increase n-level
What happens as to ionization energy as you go down a column? Explain.
Ionization energy decreases
Since n-level increases, the atomic radius increases and there is less force of attraction. Therefore, it takes less energy to remove an electron
What happens to ionization energy as you go across a column? Explain.
Ionization energy increases
Since effective nuclear charge increases (more protons), force of attraction is stronger and it takes more energy to remove an electron
Why is it easier to remove electrons from the p-orbital than the s-orbital? (lower ionization energy)
s-orbital is more likely to be closer to the nucleus which results in stronger force of attraction than p-orbital
Why does oxygen have lower ionization energy than nitrogen?
Oxygen has a paired electron orbital, whereas nitrogen has all unpaired electrons
Since paired electron orbitals create electron-electron repulsion and lower effective nuclear charge, it is easier to remove an electron since less force of attraction
Electron shielding
describes the decrease in force of attraction between the outermost electron and the nucleus due to paired electrons (greater electron-electron repulsion)
Describe electron shielding in terms of energy
Since paired electron orbitals create electron-electron repulsion, there is an increase in energy
an increase in energy indicates a decrease in force of attraction
therefore, there is less of a force of attraction due to electron shielding
Atomic number (Z)
number of protons
the total positive charge in an atom
Why is a cation smaller than its corresponding atom?
Since a cation looses an electron, each remaining electron experiences a greater effective nuclear charge from the protons
therefore, force of attraction increases and cations are smaller
Why is an anion larger than its corresponding atom?
Since an anion gains an electron, each electron experiences a lesser effective nuclear charge from the protons
therefore, force of attraction decreases and anions are larger
Why are electrons for transition metal cations removed from the s subshell instead of the d subshell?
3d is more likely to be closer to the nucleus based on radial probability, thus giving it a stronger force of attraction than 4s. Therefore, electrons are removed from 4s
f-block and shielding
the f-block are poor shielders
this creates a big increase in protons as we move down the periodic table that is unaccompanied by electrons not shielding which equals an overall higher effective nuclear charge
Why is columbs law (force) directly proportional to lattice energy?
Because to break apart a strong force of attraction it requires a greater input of energy
Why does the atomic radius not increase as you go across the transition metals?
As you add electrons to the d-block, you also increase shielding and therefore there is no net change in effective nuclear charge
Nobel peace prize winners in chem 2018
George Smith, Frances Arnold, Greg Winter
What to use when comparing force of attraction using Coulomb’s law?
Magnitude
What to use when comparing lattice energies?
Magnitude
Relationship between ionic radius and lattice energy
Ionic radius is inversely proportional to lattice energy
Why do ionic compounds want to form?
Energetically favorable
In addition, being isoelectronic with noble gas configuration provides higher Zeff and correspondingly lower potential energy
Why is energy released when a lattice forms?
Phase change from gas to solid (higher energy to lower energy)
Also, force of attraction increases, so potential energy decreases
What happens as the electron moves closer to another ion in order to form a lattice?
Force of attraction increases
Potential energy decreases
