Chemistry Topic 4 Flashcards
Bonding!
What allows ionic bonds to form?
Elements having a large difference in electronegativity
Define ionic bond
The electrostatic forces of attraction between oppositely-charged ions
How are ionic compounds arranged?
A 3D crystalline structure called an ionic lattice
What is a coordinate number?
The number of ions that surround a given ion in an ionic lattice
What is lattice enthalpy and what does it depend upon?
Lattice enthalpy is the strength of the force between ions in an ionic compound, and it depends upon the size of the ion and the charge
What is charge density?
The charge per unit volume of an ionic compound
Why do ionic compounds tend to have high melting and boiling points?
Because the electrostatic forces of attraction between ions is very strong and requires high amounts of energy to break
What two factors determine the melting point of an ionic compound?
Ionic radius and the charge on the ion
As ionic radius increases, melting point _______
Decreases!
As the charge on the ion increases, melting point ______
Increases!
Do ionic compounds tend to have high or low volatility, and why?
Low voltality because they have strong electrostatic forces of attraction
This means they do not readily escape to the vapor phase
What does electrical conductivity depend upon?
The fact that ions are able to carry a charge (freely moving charged particles)
Are ionic compounds usually brittle?
Yes! This means the crystals typically shatter when force is applies
What causes the crystal lattice to split when force is applied?
When force is applied, ions of the same charge get moved next to each other, so the repulsive forces exerted by the ions cause the lattice to split
If the difference in electronegativity increases, then ionic character ________
Increases!
What is bond length and what unit is it expressed in?
Bond length is the measure of the distance between two covalently bonded nuclei, and it is expressed in picometers (pm)
What is bond strength and what unit is it expressed in?
Bond strength is a measure of the energy required to break a covalent bond, and it is expressed in KJ/mol
Bond length and bond strength have what kind of relationship?
An inverse relationship
As you go from single to double to triple bonds, bond length (increases/decreases), and bond strength (increases/decreases)
Decreases; increases
Which bonds are stronger, shorter or longer bonds, and why?
Shorter bonds are stronger than weaker bonds because as bond length increases, the distance of the shared pair of electrons from the nucleus increases, which reduces the bond strength
What two values classify covalent bonds?
Bond length and bond strength
In a covalent bond, which side is always the slightly negative side?
The side with the atom that has a higher electronegativity because the electrons are being pulled in closer
What elements can exceed the octet rule?
Elements that are in period 3 or higher because they have d sublevels to hold “extra” electrons
When multiple atoms can exceed the octet rule, where should we place the extra lone pairs?
On the central atom
What does VSEPR stand for?
Valence Shell Electron Pair Repulsion
What is VSEPR
Not what it stands for, what it is
The shape of a molecule is due to repulsions between pairs of electrons outside the shell of the central atom
Molecules take shape to ____ repulsions
Minimize!
True or false: Bonded pairs repel more than lone pairs
False! Lone pairs repel more than bonded pairs
Do double and triple bonds repel more than single bonds?
No, they all repel the same amount
What are electron domains?
Places where bonds have formed or can form
What determines the electron geometry?
The number of electrons domains
What is the electron geometry for something with 2 domains?
Linear
What is the electron geometry for something with 3 domains?
Trigonal Planar
What is the electron geometry for something with 4 domains?
Tetrahedral
What is the electron geometry for something with 5 domains?
Trigonal Bipyramidal
What is the electron geometry for something with 6 domains?
Octahedral
What are the bond angles for a linear electron geometry?
180 degrees
What are the bond angles for a trigonal planar electron geometry?
120 degrees
What are the bond angles for a tetrahedral electron geometry?
109.5 degrees
What are the bonds angles for a trigonal bipyramidal electron geometry?
90 degrees (from top/bottom to side), 120 degrees (from side to side), and 180 degrees (from top to bottom)
What are the bond angles for an octahedral electron geometry?
90 degrees, and 180 from top to bottom
What does the bond angle become when there is one lone pair on a trigonal planar molecule?
117 degrees
What does the bond angle become when there is one lone pair on a tetrahedral molecule?
107 degrees
What does the bond angle become when there are two lone pairs on a tetrahedral molecule?
105 degrees
What are the domains around the middle called?
Equitorial
What are the domains on the top and the bottom called?
Axel
Where must you place lone pairs when drawing a trigonal bipyramidal molecule and why?
They must be put on one of the domains that is on the side, not on top or bottom. This is because lone pairs want space and these domains are furthest away from the others
What do the equitorial bond angles become on a trigonal bipyramidal when there is one lone pair present?
117 degrees because they are originally 120 degrees
What is the molecular geometry for a molecule with four domains, one of which is a lone pair?
Trigonal pyramidal
What is another name for a bent molecular geometry?
V-shape
What is the molecular geometry for a molecule with five domains, one of which is a lone pair?
Unsymmetrical tetrahedron or seesaw
What is the molecular geometry for a molecule with five domains, when two of them are lone pairs?
T-shape
Because it looks like a T
What does the equitorial bond angle become when there are two lone pairs of electrons on a molecule with five domains?
There isn’t a bond angle because there is only one equitorial bond
What is the molecular geometry for a molecule such as I3 -
Central iodine has five domains, and three lone pairs
Linear!
What do the bond angles become on a molecule with six domains, when there is one pair of lone electrons?
Less than 90 degrees
Where must you place the first two lone pairs of electrons on a molecule with 6 domains?
The top and the bottom
Which molecular shapes are symmetrical and will result in nonpolar molecules?
Linear, trigonal planar, tetrahedral, trigonal bipyramidal, square planar, octahedral
When a molecule has a charge, what will the formal charge always equal?
The charge of the molecule
Why are Boron and Beryllium considered Lewis acids?
They are electron deficient and seeking electrons
How many electrons does Boron want?
6
How many electrons does Beryllium want?
4